Helene B. Bernstein, MD, PhD George VanBuren, MD
NORMAL PREGNANCY
Pregnancy (gestation) is the physiologic process of a developing fetus within the maternal body. Several terms are used to define the developmental stage of human conception and the duration of pregnancy. For obstetric purposes, the gestational age or menstrual age is the time elapsed since the first day of the last normal menstrual period (LNMP), which actually precedes the time of oocyte fertilization. The gestational age is expressed in completed weeks. The start of the gestation (based on the LNMP) is usually 2 weeks before ovulation, assuming a 28-day regular menstrual cycle. The developmental or fetal age is the age of the conception calculated from the time of implantation, which is 4 to 6 days after ovulation is completed. The menstrual gestational age of pregnancy is calculated at 280 days or 40 completed weeks. The estimated due date (EDD) may be estimated by adding 7 days to the first day of the last menstrual period and subtracting 3 months plus 1 year (Naegele’s rule).
The period of gestation can be divided into units consisting of 3 calendar months each or 3 trimesters. The first trimester can be subdivided into the embryonic and fetal periods. The embryonic period starts at the time of fertilization (developmental age) or at 2 through 10 weeks’ gestational age. The embryonic period is the stage at which organogenesis occurs and the time period during which the embryo is most sensitive to teratogens. The end of the embryonic period and the beginning of the fetal period occurs 8 weeks after fertilization (developmental age) or 10 weeks after the onset of the last menstrual period.
Definitions
The term gravid means “pregnant”; gravida is the total number of pregnancies that a women has had, regardless of the outcome. Parity is the number of births, both before and after 20 weeks’ gestation, and comprises 4 components:
1. Full-term births
2. Preterm births: having given birth to an infant (alive or deceased) weighing 500 g or more, or at or beyond 20 completed weeks (based on the first day of the last menstrual period)
3. Abortions: pregnancies ending before 20 weeks, either induced or spontaneous
4. Living children
When gravidity and parity are calculated as part of the obstetric history, multiple births are designated as a single gravid event, and each infant is included as part of the parity total.
Live birth is the delivery of any infant (regardless of gestational age) that demonstrates evidence of life (eg, a heartbeat, umbilical cord pulsation, voluntary or involuntary movement), independent of whether the umbilical cord has been cut or the placenta detached. An infant is a live-born human from the moment of birth until the completion of 1 year of life (365 days).
A preterm infant is defined as one born between 20 weeks and 37 completed weeks of gestation (259 days). A term infant is one born between 37 0/7 and 40 0/7 weeks gestation (280 days). At term, a fetus usually weighs more than 2500 g. Depending on maternal factors such as obesity and diabetes, amniotic fluid volume, and genetic and racial factors, the baby may be larger or smaller than expected; therefore, the clinician must rely on objective data to determine fetal maturity. Fetal lung maturity is assumed after 39 weeks’ gestation but can be verified at an earlier gestational age by analysis of amniotic fluid by amniocentesis.
A postterm infant is born after 42 weeks’ gestation (294 days). A prolonged pregnancy may result in an excessive-size infant with diminished placental capacity. A postmature infant may exhibit characteristic cutaneous changes, including a loss of subcutaneous fat, wrinkled skin, and fine long hair on the arms. Predicting the end of a pregnancy is a difficult problem for prenatal care providers. Prenatal mortality rates increase as gestation advances past the due date (EDD) and accelerates sharply after 42 weeks’ gestation. It is not uncommon to offer induction of labor after 41 completed weeks, or 7 days past the due date. (See Chapter 14 on Late Pregnancy Complications.) Estimated gestational age can be determined by methods outlined later for ascertaining fetal age and EDD.
Increased morbidity and mortality may be associated with a macrosomic infant or a large for gestational age (LGA) fetus. This is defined as a fetus with an estimated fetal weight at or beyond the 90th percentile at any gestational age. At term, approximately 10% of newborn infants weigh more than 4000 g, and the weight of 1.5% of newborns is in excess of 4500 g. Excessive fetal size should be suspected in women with a previous macrosomic fetus or those with diabetes mellitus. A low-birth-weight infant is any live birth for which the infant’s weight is less than or equal to 2500 g. An infant with fetal growth restriction is defined as one at or below the 10th percentile at any gestational age.
Using a system based on the duration of gestational age or fetal weight, an abortion is the expulsion or extraction of part (incomplete) or all (complete) of the placenta or membranes without an identified fetus or with a fetus (alive or deceased) weighing less than 500 g or with an estimated gestational age of less than 20 completed weeks or 139 days from the last menstrual period, if fetal weight is unknown.
A. Birth Rate & Fertility Rate
Birth rate is defined as the number of live births per 1000 population. The fertility rate is expressed as the number of live births per 1000 women ages 15–44 years (sexually active population group). The current birth rate is 13.83 per 1000 population in 2010, whereas the general fertility rate is 66.7 per 1000 women ages 15–44 years.
B. Neonatal & Perinatal Periods
The neonatal period is defined as birth until 28 days of life; during this interval, the infant is designated as a newborn or neonate. The perinatal period is the time from 28 weeks’ gestation to the first 7 days of life; this also includes the late fetal and early neonatal period.
The prenatal mortality rate is the sum of late fetal deaths plus early neonatal deaths (death in the first 7 days of life). The neonatal mortality rate (NMR) is infant death from birth to within 28 days of life. The NMR is calculated as the number of neonatal deaths during a year, divided by the number of live births during the same year, expressed per 1000 live births.
American College of Obstetricians and Gynecologists. Fetal Macrosomia. ACOG Practice Bulletin No. 22. Obstet Gynecol 2000;96.
Centers for Disease Control and Prevention. National Center for Health Statistics. http://www.cdc.gov/nchs/data_access/Vitalstatsonline.htm#Downloadable. Accessed January 10, 2011.
ESSENTIALS OF DIAGNOSIS
Diagnosis is made on the basis of amenorrhea and a positive pregnancy test.
It is crucial to diagnose pregnancy as soon as possible in order to initiate appropriate prenatal care, avoid teratogen (an agent that can cause a deleterious fetal effect) exposure, and diagnose nonviable or ectopic pregnancies.
Clinical Findings
A. Symptoms & Signs
A number of clinical signs and symptoms may presumptively indicate pregnancy.
1. Amenorrhea—Cessation of menses is caused by hormones (estrogen and progesterone) produced by the corpus luteum. The abrupt cessation of menses in a healthy reproductive-aged female with predictable cycles is highly suggestive of pregnancy.
2. Nausea & vomiting—This is a common symptom (50% of pregnancies) that begins as early as 2 weeks’ gestational age and customarily resolves at between 13 and 16 weeks’ gestation. Hyperemesis gravidarum is an extreme form of nausea and vomiting and is characterized by dehydration, weight loss (up to 5%), and ketonuria. In extreme cases of hyperemesis gravidarum, hospitalization, intravenous therapy, antiemetics, and, if needed, parenteral nutrition are given. Uncomplicated nausea and vomiting is treated with frequent small meals, a dry diet, and emotional support. (See Chapter 29 on Gastrointestinal Disorders in Pregnancy for more discussion.)
3. Breast changes
A. MASTODYNIA—Breast tenderness may range from tingling to pain caused by hormonal changes affecting the mammary duct and alveolar system.
B. BREAST ENGORGEMENT—Breast engorgement and periareolar venous prominences are also seen early in pregnancy, especially in primiparous patients. Montgomery’s tubercles are the portion of the areolar glands visible on the skin surface. These tubercles can be more pronounced during pregnancy secondary to hormonal changes occurring as early as 6–8 weeks’ gestation.
C. COLOSTRUM SECRETION—Protein and antibody production may occur during pregnancy as early as 16 weeks’ gestation. This secretion is not associated with preterm delivery.
D. DEVELOPMENT OF SECONDARY BREAST TISSUE—Development of secondary breast tissue may occur across the nipple line. Hypertrophy of secondary breast tissue may occur in the axilla and cause a symptomatic mass.
4. Fetal movement—The initial perception of fetal movement occurs at 18–20 weeks’ gestation in primiparous patients and as early as 14 weeks’ gestation in multiparous patients. Maternal perception of movement is called quickening, but this is not a dependable sign of pregnancy.
5. Elevated basal body temperature—Progesterone produces a 0.5°F increase in the basal body temperature, which persists after the missed menses. The rise in temperature occurs within the luteal phase of the menstrual cycle.
6. Skin changes
A. CHLOASMA—The mask of pregnancy is skin darkening of the forehead, bridge of the nose, or cheek bones. This pregnancy-associated change is linked to genetic predisposition and usually occurs after 16 weeks’ gestation. Chloasma is exacerbated by sunlight.
B. LINEA NIGRA—Melanocyte-stimulating hormone increases, causing darkening of the nipples and the lower midline from the umbilicus to the pubis (linea nigra). This skin change is genetically based; skin lightens slightly after delivery of the fetus.
C. STRIAE—Striae marks of the breast and abdomen appear as irregular scars. The striae appear late in pregnancy and are caused by collagen separation.
D. SPIDER TELANGIECTASIA—These are common skin lesions of pregnancy that result from elevated plasma estrogen. Both the vascular stellate skin lesions as well as palmar erythema may be seen in pregnancy and also occur in patients with liver failure.
7. Pelvic organ changes
A. CHADWICK’S SIGN—Congestion of the pelvic vasculature causes bluish discoloration of the vagina and the cervix. This is a presumptive sign of pregnancy.
B. HEGAR’S SIGN—There is widening and softening of the body or isthmus of the uterus. This occurs at 6–8 weeks’ menstrual age or gestational age. Estrogen and progesterone cause increased cervical softening and dilation at the external os.
C. LEUKORRHEA—There is an increase in vaginal discharge, containing epithelial cells and cervical mucous, secondary to hormonal changes.
D. PELVIC LIGAMENTS—There is relaxation of the sacroiliac and pubic symphysis during pregnancy. Relaxation is pronounced at the pelvic symphysis.
E. ABDOMINAL ENLARGEMENT—There is progressive abdominal enlargement with growth of uterus during pregnancy. From 18 to 34 weeks there is a good correlation between the uterine fundal measurement in centimeters and the gestational age in weeks.
F. UTERINE CONTRACTIONS—Painless uterine contractions (Braxton Hick’s contractions) are felt as tightening or pressure. They usually begin at approximately 28 weeks’ gestation and increase in regularity with advancing gestational age. These contractions usually disappear with walking or exercise, whereas true labor contractions become more intense.
DIAGNOSIS
A. Fetal Heart Tones
Fetal heart tones (FHTs) are detectable by handheld Doppler (after 10 weeks’ gestation) or by fetoscope (after 18–20 weeks’ gestation). The normal heart rate is 110–160 beats per minute, with a higher fetal heart rate observed early in pregnancy.
B. Uterine Size/Fetal Palpation
Uterine size can be used to diagnose pregnancy secondary to uterine enlargement. Later in pregnancy, the fetus can be palpated through the maternal abdominal wall (after 22 weeks), and the position can be determined by Leopold’s maneuvers.
C. Imaging Studies
Sonography is one of the most useful technical aids in diagnosing and monitoring pregnancy. Cardiac activity is discernible at 5–6 weeks via transvaginal sonogram, limb buds at 7–8 weeks, and finger and limb movements at 9–10 weeks. At the end of the embryonic period (10 weeks by LNMP), the embryo has a human appearance. The gestational age can be determined by the crown rump length between 6 and 13 weeks’ gestation, with a margin of error of approximately 8% or 3–5 days.
D. Pregnancy Tests
Sensitive, early pregnancy tests measure changes in the level of human chorionic gonadotropin (hCG). There is a small degree of cross-reactivity between luteinizing hormone, follicle-stimulating hormone, and thyrotropin, which all share an α subunit with hCG. The β submit of hCG is produced by the syncytiotrophoblast 8 days after fertilization and may be detected in the maternal serum 8–11 days after conception or as early as 21–22 days after the LNMP. β-hCG levels peak at 10–12 weeks’ gestation and decrease afterward. The half-life of hCG is 1.5 days. Generally, serum and urine levels return to normal (<5 mIU/mL), 21–24 days after delivery or after a fetal loss.
1. Home pregnancy test—hCG is a qualitative test that is performed on the first voided morning urine sample. A positive test is usually indicated by a color change. Because the accuracy of the home pregnancy test depends on technique and interpretation, it should always be repeated in the office.
2. Urine pregnancy test—An antibody assay recognizing the β-hCG subunit is the initial lab test performed in the office to diagnose pregnancy. The test is reliable, rapid (1–5 minutes), and inexpensive, with a positive test threshold between 5 and 50 mIU/mL, characterized by a color change. This is the most common method to confirm pregnancy.
3. Serum pregnancy test—β-hCG can be detected within 7 days after conception or at a menstrual age of 21 days’ gestation. The threshold for a positive test can be as low as 2–4 mIU/mL. Serial quantitative tests of β-hCG are be used to evaluate threatened abortion, ectopic pregnancy, or a molar pregnancy.
GESTATIONAL AGE DETERMINATION
The EDD (estimated date of delivery) and gestational age should be established based on the LNMP and Naegele’s rule. Clinical parameters, discussed later, should be used as an adjunct to confirm or establish dating as needed.
Pregnancy Calendar or Calculator
Normally, human pregnancy lasts 280 days or 40 weeks (9 calendar months or 10 lunar months) from the LNMP. This may also be calculated as 266 days or 38 weeks from the last ovulation in a normal 28-day cycle. The easiest method of determining gestational age is with a pregnancy calendar or calculator. The EDD can be determined mathematically using Naegele’s rule: subtract 3 months from the month of the LNMP and add 7 to the first day of the LNMP. Example: With an LNMP of July 14, the EDD is April 21.
CLINICAL PARAMETERS
Ultrasound
Ultrasound is used routinely to determine viability, estimate gestational age, screen for aneuploidy, and evaluate fetal anatomy and well-being. From 13 to 20 weeks, the most accurate parameter for gestational age assessment is the biparietal diameter, although this measurement is often used together with the head circumference, abdominal circumference, and femur length, with a margin of error (secondary to measurement) of 8% or approximately 7 days. After 24 weeks’ gestation, the accuracy of ultrasound to estimate gestational age is diminished and is best used to assess growth or the estimated fetal weight.
Indications for ultrasound are as follows:
1. Dating.
2. Aneuploidy assessment—Discussed in Screening section (later).
3. Anatomical survey—A comprehensive anatomical survey can be performed as early as 16–18 weeks’ gestation.
4. Cervical length assessment.
5. Fetal well-being can be monitored by ultrasound using the biophysical profile.
Uterine Size
An early first-trimester examination usually correlates well with the estimated gestational age. The uterus is palpable just at the pubic symphysis at 8 weeks. At 12 weeks, the uterus becomes an abdominal organ, and at 16 weeks, it is usually at the midpoint between the pubic symphysis and the umbilicus. Between 18 and 34 weeks’ gestation, the uterus size or fundal height is measured in centimeters from the pubic symphysis to the upper edge of the uterine corpus, and the measurement correlates well with the gestational age in weeks (Fig. 6–1). The uterus is palpable at 20 weeks at the umbilicus. After 36 weeks, the fundal height may decrease as the fetal head descends into the pelvis.
Figure 6–1. Height of fundus at various times during pregnancy.
Quickening
Maternal perception of fetal movement occurs between 18 and 20 weeks in the primiparous patient and at 14–18 weeks in the multigravida. The perceived fetal movement, or quickening, is often described as a butterfly-like movement rather than a kick.
Fetal Heart Tones
FHTs may be heard by a fetoscope at 18–20 weeks and by Doppler ultrasound as early as 10 weeks’ gestation.
PREGNANCY FAILURE
Early
A. Diagnosis
The gold standard for diagnosis of early pregnancy failure is ultrasound. Definitive diagnosis requires recognition of a fetus in the absence of cardiac activity.
B. Laboratory Findings
In cases where ultrasound findings are equivocal, serial measurements of serum β-hCG levels with a failure to demonstrate an appropriate increase are helpful.
Late
C. Signs and Symptoms
In late pregnancy, the first sign of fetal demise is usually the absence of fetal movement as noted by the mother.
D. Diagnosis
If FHT cannot be appreciated, real-time ultrasonography is virtually 100% accurate in describing the absence of fetal heart motion.
E. Complications
Disseminated intravascular coagulopathy is a rare sequelae occurring after an intrauterine fetal demise (IUFD). Coagulation studies may be started 2 weeks after the demise of one twin, and delivery can be undertaken if serial serum fibrinogen levels fall below 200 mg/dL. In a singleton IUFD, coagulation studies including fibrinogen are done immediately after the diagnosis is made, and delivery is initiated promptly.
American College of Obstetricians and Gynecologists. Ultrasonography in Pregnancy. ACOG Practice Bulletin No. 101. Obstet Gynecol 2009;113:451–461. PMID: 19155920.
Owen J, Yost N, Berghella V, et al. Mid-trimester endovaginal sonography in women at high risk for spontaneous preterm birth. JAMA 2001;286:1340–1348. PMID: 11560539.
Wilcox AJ, Baird DD, Dunson D, McChesney R, Weinberg CR. Natural limits of pregnancy testing in relation to the expected menstrual period. JAMA 2001;286:1759–1761. PMID: 11594902.
PRENATAL CARE
Pregnancy is a normal physiologic process; however, complications that increase the mortality or morbidity to the mother and/or fetus occur in 5–20% of pregnancies. Our present system of prenatal care focuses on prevention.
Prenatal care providers must be familiar with the normal changes of pregnancy and the possible pathologic changes that may occur so that therapeutic measures can be initiated to reduce any risks to the mother or fetus. The purpose of prenatal care is to ensure a successful pregnancy outcome when possible, including the delivery of a live, healthy fetus. It’s proven that mothers receiving prenatal care have a lower risk of complications, and one of the principal aims of prenatal care is the identification and special treatment of the high-risk patient—the one whose pregnancy, because of some factor in her medical history or an issue that develops during pregnancy, is likely to have a poor outcome.
Ideally, a woman planning pregnancy should have a medical evaluation before conception; this allows the physician to determine whether any risk factors will complicate a pregnancy in the context of a complete history and physical examination, along with prenatal laboratory studies. During the medical evaluation, the risks of cigarette smoking, alcohol and drug use, and exposure to known teratogens are discussed. Instructions on nutrition, exercise, and vitamins can be provided before pregnancy. For example, folic acid taken 3 months before conception may be beneficial in decreasing the incidence of open neural tube defects and cardiac anomalies.
Most women do not have a preconception evaluation, and the first prenatal visit may be scheduled well into the first and occasionally in the second or third trimester. Factors for delayed medical care should be reviewed with the patient, and any barriers—whether social, financial, or cultural—may be addressed for this and future pregnancies.
INITIAL OFFICE VISIT
The purpose of the first office visit is to identify any risk factors influencing the mother and/or fetus. A plan of care for a high-risk pregnancy may be established at the first prenatal visit, including pertinent consultations of subspecialists.
HISTORY
A. Obstetric History
The interview should include a discussion of current symptoms; this is also an ideal time to discuss any perceptions regarding childbearing (including potential birth plans) and the effect of the pregnancy on the patient’s life.
Outcomes of all previous pregnancies provide important information for the current pregnancy; the following information should be obtained: length of gestation, birth weight, length of labor, type of delivery, fetal/neonatal outcome, anesthesia, and any complications occurring in previous pregnancies, including pregnancies ending before 20 weeks’ gestation. If a caesarean section was performed, an operative report detailing the type of incision and any intraoperative complications should be obtained.
B. Medical History
Pregnancy may influence a number of maternal organ systems, and preexisting conditions may be exacerbated during pregnancy. Many cardiovascular, gastrointestinal, and endocrine disorders require careful evaluation and consultation regarding effects on the mother. For example, a prior blood transfusion may increase the risk of hemolytic disease of the newborn because of maternal antibodies produced secondary to a minor blood group mismatch. Medical conditions of particular relevance to pregnancy include diabetes and other endocrine diseases, hypertension, epilepsy, and autoimmune diseases.
C. Surgical History
A history of previous gynecologic, abdominal, or uterine surgery may necessitate a caesarean section. In addition, a history of cervical surgery, multiple induced abortions, or recurrent fetal losses may suggest cervical incompetence. Patients with a previous caesarean section may be candidates for vaginal delivery if they are adequately counseled and meet established guidelines.
D. Family History
A family history of diabetes mellitus should alert the clinician about an increased risk of gestational diabetes, especially if the patient has a history of a large infant or a previous birth defect, or an unexplained fetal demise. Glucose testing should be performed at the initial prenatal visit if there is a strong suspicion of undiagnosed pregestational diabetes rather than waiting until 24–28 weeks’ gestation.
Awareness of familial disorders is also important in pregnancy management. Thus a brief, 3-generation pedigree is useful. Antenatal screening tests are available for many hereditary diseases. A history of twinning is important, because dizygotic twinning (polyovulation) may be a maternally inherited trait.
E. Social History
The prenatal history should include documentation of tobacco and alcohol use, any contact with intravenous drugs or drug users, or other drug use. Exposures (workplace and otherwise) should be evaluated.
Physical Examination
A complete physical examination should be performed at the first obstetric or prenatal visit; the pelvic examination is of special importance for the obstetrician, nurse, or midwife.
1. Bony pelvis—The configuration should be evaluated to determine whether the patient is at risk for cephalopelvic disproportion, which may lead to an operative delivery. Pelvimetry has been largely replaced, however, by clinical evaluation of the pelvis (“trial of labor”).
A. PELVIC INLET—The anteroposterior diameter or diagonal conjugate may be estimated at the time of the initial pelvic examination. For this measurement, the index and middle finger are inserted into the vagina, the middle finger reaches the sacral promontory, and the tissue between the examiners’ index and thumb is pushed against the patient’s pubic symphysis. The distance between the tip of the examiner’s finger and pubic symphysis pressure on the thumb measures the diagonal conjugate; the anterior diameter of the pelvic inlet is estimated by subtracting 1.5 cm from the measured diagonal conjugate (Fig. 6–2).
Figure 6–2. Measurement of the diagonal conjugate (conjugata diagonalis). (Reproduced, with permission, from Benson RC. Handbook of Obstetrics & Gynecology. 8th ed. Los Altos, CA: Lange; 1983.)
B. MIDPELVIS—The midpelvic space can be estimated by noting the prominence and closeness of the ischial spines. If the walls of the pelvis converge, and if the curve of the sacrum is straight/shallow, or if the sacrosciatic notches are narrowed, the midpelvis may be inadequate for a vaginal delivery.
C. PELVIC OUTLET—In contrast to the midpelvis, the pelvic outlet can be estimated by a physical examination. The shape of the outlet can be determined by palpitation of the pubic rami from the symphysis to the ischial tuberosities with an estimation of the angle of the rami. A subpubic angle of less than 90 degrees suggests an inadequate pelvic outlet. A prominent coccyx decreases the anterior posterior diameter of the outlet and may further diminish the pelvic outlet.
2. Uterus—The uterus can be used to confirm gestational age in the first half of pregnancy. As the uterus enlarges, it becomes globular and often rotates to the right.
3. Cervical length—A nulliparous woman who has not undergone a vaginal delivery will have a closed external cervical os. A multiparous patient may have a greater opening or dilation of the external os. The average cervical length by bimanual examination in women averages between 3 and 4 cm. Women with a previous history of spontaneous preterm birth may undergo a transvaginal sonogram (TVS) during the second trimester to evaluate her risk of recurrent preterm birth. Serial TVS exams may be necessary if there is any evidence of cervical dilation or cervical shortening on the initial sonogram.
4. Adnexal exam—During the pelvic exam, a bimanual examination is performed, and the cervical length and evaluation of both ovaries (the adnexa) can be performed.
Laboratory Tests
A. Initial Blood Tests
At the first prenatal visit, a number of screening tests are performed, including a complete blood count (hemoglobin, hematocrit, and platelets), blood group and Rh typing (ABO/Rh), screen for antibodies against blood group antigens, VDRL (Venereal Disease Research Laboratory) or RPR (rapid plasma reagent) for syphilis, hepatitis B surface antigen, and serology to detect antibodies against rubella and HIV. Women with a history of gestational diabetes are given a glucose challenge test (GCT) with oral ingestion of a solution containing 50 g of glucose. The venous glucose level is checked 1 hour after glucose ingestion.
B. Genetic Screening and Testing
1. Screening—First-trimester screening using a combination of a fetal nuchal translucency measurement and maternal serum analysis of pregnancy-associated plasma protein A (PAPP-A) and free or total β-hCG is used to screen for trisomy (21, 18, and 13). The detection rate of aneuploidy is between 85% and 87%, with a false-positive rate of less than 5%. With the use of first-trimester screening, maternal serum α fetoprotein (AFP) should be drawn at 15–18 weeks’ gestation to screen for open neural tube defects.
For patients desiring aneuploidy assessment who did not receive first-trimester screening, a second trimester maternal serum quad screen is offered between 15 and 20 weeks’ gestation (ideally at 16–18 weeks) to screen for neural tube defects and aneuploidy (chromosomal abnormalities). Analytes studied include serum β-hCG, unconjugated estriol, AFP, and inhibin. The detection rate of a quad screen is between 65% and 75% for trisomy 21, 18, and 13 and between 80% and 85% for open neural tube defects. The false-positive rate is approximately 5%.
Additional genetic testing includes hemoglobin electrophoresis to screen for hemoglobinopathies (including sickle cell disease risk) and cystic fibrosis screening, which has been added to prenatal screening at many institutions.
2. Invasive genetic testing—Invasive genetic testing must be offered to all women, especially those who will be 35 years of age or older at the time of delivery or who have a history of an abnormal pedigree or risk factors for inherited diseases. Chorionic villous sampling is performed between 9 and 13 weeks’ gestation by either transabdominal or transvaginal technique. Amniocentesis is usually offered at between 15 and 20 weeks’ gestation. The complication rate of these procedures is less than 1%, and the detection rate for aneuploidy is greater than 99%.
C. Urine Testing
At the initial prenatal visit, urinalysis and culture is performed. Approximately 2–12% of pregnant women have an asymptomatic urinary tract infection. If the bacterial count is greater than 105/mL, expressed as colony-forming units (CFU) on a voided specimen, then antibiotic sensitivity is performed.
Testing for urinary protein, glucose, and ketones is performed at each prenatal visit. Proteinuria of greater than or equal to 2+ on a standard dipstick (which correlates to greater than 300 mg/24 hours on a timed urine collection) may indicate renal disease or the onset of preeclampsia. The presence of glucosuria signifies that glucose transport to the kidney exceeds the transport capacity of the kidneys. This generally does not have clinical significance unless carbohydrate intolerance or gestational diabetes is present. During pregnancy in a known diabetic patient, the presence of urinary ketones usually indicates inadequate carbohydrate intake. In this case, the patient’s diet should be reevaluated to ensure adequate carbohydrate intake.
D. Papanicolaou Smear (PAP)
Cervical cancer screening is performed at the initial prenatal visit unless there has been a normal exam within the past year.
E. Tuberculin Skin Test
A tuberculin skin test (purified protein derivative) is appropriate for high-risk patients.
E. Sexually Transmitted Diseases
1. Syphilis—Tests performed at the initial prenatal visit such as VDRL and the RPR screen in a sensitive, nonspecific manner for Treponema pallidum. A treponemal antibody test (FTA-ABS) is used to confirm syphilis infection after a positive VDRL or RPR screen in the absence of confirmed prior infection. Penicillin is the treatment of choice in pregnancy because of the ability of the agent to cross the placenta and treat the fetus as well as the mother. Erythromycin or ceftriaxone are alternative treatments outside of pregnancy, but penicillin is the treatment of choice for pregnant women. Because of the risk of treatment failure with secondary agents and congenital syphilis infection, penicillin desensitization is indicated in the setting of anaphylactic allergy. Monthly serologic tests (VDRL or RPR) are followed to assess treatment success of syphilis. These tests can remain positive after treatment; however, their titer should decrease substantially. The FTA-ABS will remain positive even after successful treatment.
2. Chlamydia—Screening consists of a DNA probe, which has a 90% specificity and sensitivity. An endocervical sample or urine sample can be used for diagnosis of chlamydia (CT). The agent of choice is azithromycin (1 g oral dose). Amoxicillin (500 mg oral dose three times a day for 7 days) is an alternative treatment. A test of cure is performed 2–3 weeks after completion of treatment. Screening for gonorrhea (GC) and CT are routinely performed at the time of PAP smear. In a high-risk population, these cultures are repeated at the third trimester (35–37 weeks’ EGA).
3. Gonorrhea—GC can be detected by culture of the organism in Thayer-Morton agar or by a DNA probe as part of a combined GC/CT. GC may be transmitted to the infant and cause ophthalmic injury. Infection may be associated with preterm labor, preterm premature rupture of membranes, and intrapartum as well as postpartum infection. The drug of choice is ceftriaxone (125 mg intramuscularly [IM] onetime dose or 1 g intravenously every 24 hours for disseminated disease) secondary to prevalent penicillin-resistant strains. Patients with an allergy to penicillin are treated with a 2-g IM dose of spectinomycin.
4. Herpes simplex virus—Tissue culture or DNA polymerase chain reaction are used to detect active herpetic infections; serology can be used to assess a history of exposure. Oral acyclovir is used for primary and recurrent outbreaks. Prophylactic treatment at 36 weeks’ gestation for women with documented genital herpes and recurrent outbreaks is recommended to reduce the chance of the patient having an active outbreak when she presents in labor. Regimens commonly used are acyclovir 400 mg twice daily or valacyclovir 1000 mg daily. When a patient is admitted for delivery, she should be asked about prodromal symptoms and examined for lesions of the cervix, vagina, and perineum. If no lesions or symptoms are present, vaginal delivery is permitted.
5. HIV—All obstetric patients should undergo HIV screening on an “opt out” basis at the first prenatal visit. The initial HIV screening test is an enzyme-linked immunosorbent assay (ELISA) followed by a confirmatory Western blot or immunofluorescence assay for patients with ELISA-positive tests.
If a woman has not had prenatal HIV testing (or care), a rapid HIV test is offered at the time of hospital admission. The goal of prenatal care and treatment of the HIV-positive pregnant patient is to appropriately treat the mother, reduce viral load, and minimize perinatal HIV transmission by providing antiretroviral prophylaxis intrapartum and to the infant. Treatment regimens should include prenatal highly active anti-retroviral therapy and intrapartum infusion of azidothymidine. Ongoing assessment of an HIV-infected pregnant woman involves serial measurements of the viral load and CD4 T-cell count. Cesarean delivery is recommended only for patients with high viral load (>1000 copies/mL); otherwise, mode of delivery is dictated by obstetric indications.
6. Other infections
A. TRICHOMONAS—Trichomonas vaginalis can be identified in 20–30% of pregnant patients, but only 5–10% of patients are symptomatic (itching, burning, or discharge). T vaginalis is a flagellated ovoid organism seen under magnification in warm normal saline solution. The discharge is described as foamy green and malodorous. Metronidazole has an efficacy of approximately 95% against T vaginalis. Metronidazole may be given as a single oral dose of 2 g, 500 mg twice daily for 7 days, or 250 mg 3 times daily for 7 days.
B. CANDIDIASIS—Candida albicans can be cultured from the vagina of many immunocompromised women (HIV, insulin-dependent diabetes mellitus, or pregnant). Symptoms of vaginal candidiasis include vaginal burning, itching, and a thick, white, curd-like discharge. Marked inflammation of the vagina and perineum may be noted, but fewer than 50% of women have symptoms.
The confirmatory test for candida is microscopic detection of hyphae or yeast buds on a KOH preparation. For uncomplicated candida yeast infections, topical therapy may be given for 3–7 days with agents such as miconazole, terconazole, clotrimazole, and butoconazole. In refractory cases, administration of systemic agents may be considered. Fluconazole (150-mg single oral dose) is the preferred agent in pregnancy.
C. BACTERIAL VAGINOSIS—Bacterial vaginosis (BV) is responsible for a large percentage of vaginitis during pregnancy. BV is a polymicrobial infection that is associated with many complications of pregnancy, including preterm labor, preterm premature rupture of membranes, chorioamnionitis, and endometritis.
SUBSEQUENT VISITS
The frequency of office visits is dependent on the gestational age, maternal condition, and any fetal complications. The standard schedule for prenatal office visits in uncomplicated patients is every 4 weeks from 0 to 32 weeks’ gestation, every 2 weeks from 32 to 36 weeks’ gestation, and weekly visits after 36 weeks’ gestation.
At each visit, maternal weight, uterine fundal height, maternal blood pressure, and urinalysis by dipstick are documented. The FHTs should be documented. All findings should be recorded and compared with those from previous visits.
Maternal Weight Gain
The prepregnancy weight and the amount of weight gain during pregnancy are important. Maternal weight gain during pregnancy is due to a number of factors. The fetus (on average, 3500 g at term), the placenta (650 g) amniotic fluid (800 mg), breast enlargement (400 g) and uterus (970 g) are factors, as well as increased interstitial fluid and blood volume, which results in an additional 1200–1800 g of weight gain.
A woman who is 15% or more below ideal body weight or of short stature has a risk for a small for gestational age (SGA) infant and preterm delivery. A pregnant adolescent may have maternal compromise, as well as fetal jeopardy, if her diet is inadequate to meet her own growth requirements as well as that of the fetus. Inadequate maternal weight gain may reflect poor nutrition, inadequate nutrition absorption, or maternal illness, predisposing the mother to an inadequate volume expansion and the fetus to growth restriction. The American College of Obstetrics and Gynecology recommend a weight gain of 11.5–16 kg (25–35 lb) during a singleton pregnancy. Underweight women should gain more weight (12.5–18 kg or 28–40 lb), whereas obese women should gain less than 7–11.5 kg or 15–25 lbs.
Obese women (>30 body mass index [BMI]) and those with excessive maternal weight gain during pregnancy are more likely to have a macrosomic infant when compared with women with a normal BMI and appropriate weight gain during pregnancy.
Blood Pressure
The blood pressure tends to decrease 5–7 mm (both systolic and diastolic components) early in the second trimester, but the blood pressure measurement returns to normal levels in the third trimester. Blood pressure changes may provide a subtle sign of vascular compromise. Elevation of blood pressure may precede an increase in proteinuria seen with hypertension in pregnancy. Blood pressure is most accurately measured in a sitting position (with the arm at the level of the heart).
Fundal Height
There is a connection between the uterine size or fundal height (in centimeters) and the gestational age (in weeks) between 18 and 34 weeks. Measurement is made from the pubic symphysis to the top of the uterus (McDonald’s technique). Fundal height is measured at each visit after 20 weeks’ gestation. If the fundal height is discordant from the estimated gestational age by more than 2 (centimeters or weeks), further evaluation of fetal size and amniotic fluid via ultrasound is warranted.
Fetal Heart Tones
FHTs can be auscultated by 10–12 weeks’ gestation using a handheld Doppler device; while in use, attention should be paid to the rate, rhythm, and presence of any irregularity of heart rate, as well as accelerations or decelerations. Abnormalities in rate or rhythm should be evaluated by ultrasound, electronic fetal heart rate monitoring, or even a fetal echocardiogram.
Edema
At each prenatal visit, findings should be noted, including transient episodes of general edema or swelling. Lower extremity edema in late pregnancy is a natural consequence of hydrostatic changes in lower body circulation. Edema of the upper body (eg, face and hands), especially in association with relative or absolute increases in blood pressure, may be the first sign of preeclampsia, although edema is not part of the current diagnostic criteria. A moderate rise in blood pressure without excessive fluid retention may suggest a predisposition to chronic hypertension.
Fetal Size & Position
Manual assessment of fetal size and position is always indicated after approximately 26 weeks’ gestation. The fetus may assume a number of positions before late gestation, but persistence of an abnormal lie into late pregnancy suggests abnormal placentation, uterine anomalies, or other problems that should be investigated by ultrasound. If an abnormal lie persists, consider external version after 37 weeks’ gestation.
Laboratory Evaluations
A. Third-Trimester Laboratory Studies
1. Gestational diabetes screening—A 1-hour GCT, with a 50-g glucose load, is given between 24 and 28 weeks’ gestation. If the 1-hour glucose test is abnormal, a 3-hour glucose tolerance test is performed. A 100-g glucose load is ingested after obtaining a fasting glucose level. Venous glucose levels are then measured at 1, 2, and 3 hours after the glucose load.
2. Complete blood count—This is normally repeated at the beginning of the third trimester to evaluate for anemia.
3. Group B streptococcus—The current recommendation is to perform routine screening for group B streptococcus (GBS) between 35 and 37 weeks’ gestation. If the patient has a positive GBS culture at 35–37 weeks, or a positive urine culture for GBS anytime during the pregnancy, the patient is treated with penicillin (the drug of choice in the absence of allergy) at the time of admission in labor, decreasing the risk of early-onset group B streptococcal sepsis in the newborn.
COMMON COMPLAINTS
Ptyalism
Excessive salivation may be a complaint in a small percentage of pregnant women. The cause is unknown but may be associated with nausea and vomiting.
Pica
Pica is the ingestion of substances with no nutritive value; some common examples are ingestion of clay or laundry starch. Pica is harmful, as nutrition may be inadequate with the ingestion of nonnutritious bulk.
Urinary Frequency & Renal Function
Urinary frequency is a common complaint throughout pregnancy. Late in pregnancy, the enlarging uterus and fetus decrease bladder capacity, leading to frequency. The glomerular filtration rate increases 50% during pregnancy, and the serum creatinine decreases to a level of 0.4–0.6 mg/dL. Both the altered bladder and kidney function result from hormonal changes associated with pregnancy. Dysuria or hematuria may be a sign of infection. Approximately 2–12% of pregnant women have a urinary tract infection without symptoms. Diagnosis of a urinary tract infection will require a urinalysis as well as a urine culture with bacterial sensitivity.
Varicose Veins
Pressure by the enlarging uterus, which reduces venous return, as well as the relaxation of vascular smooth muscle by progesterone may result in enlargement of the peripheral veins in the lower extremities and development of varicosities. Specific therapy includes elevation of the lower extremities and the use of thigh-high compression stockings. These measures may reduce the degree of lower extremity edema and varicosity. Superficial varicosity is not evidence of deepvenous thrombosis.
Joint & Back Pain
During pregnancy, relaxation may result in a small degree of separation or mobility at the pubic symphysis and sacroiliac articulations. The pregnant patient may experience an unstable pelvis, which results in pain. A pelvic girdle or maternity sling with bed rest may partially relieve the pelvic pain. The increasingly protuberant maternal abdomen results in lordosis. The patient may compensate the lordosis with backward thrust of the shoulders and forward thrust of the head. The corrective position may result in an exaggerated curvature of the maternal spine. A maternity girdle and low-heeled support shoes may reduce the back pain. Exercise and physical therapy may be helpful.
Leg Cramps/Numbness
Leg cramps are a common complaint with an unknown etiology. Theories for leg cramps include a reduced level of serum calcium or magnesium. Treatments include nutritional supplementation of calcium carbonate or calcium lactate. Magnesium citrate (300 mg per day) has also been used for leg cramps. Other therapies include local heat, massage, or flexion of the feet.
Breast Soreness
Physiologic breast engorgement may cause discomfort, especially during early and late pregnancy. A well-fitting brassiere worn 24 hours a day affords relief. Ice bags are temporarily effective. Hormone therapy is of no value.
Discomfort in the Hands
Acrodysesthesia of the hands consists of periodic numbness and tingling of the fingers (the feet are never involved). It affects at least 5% of pregnant women. In some cases it is thought to be a brachial plexus traction syndrome caused by drooping of the shoulders during pregnancy; carpal tunnel syndrome is a common cause of a similar symptom complex. The discomfort is most common at night and early in the morning. It may progress to partial anesthesia and impairment of manual proprioception. The condition is apparently not serious, but it may persist after delivery as a consequence of lifting and carrying the baby.
OTHER ISSUES RELATED TO PRENATAL CARE
Bathing
Bath water generally does not enter the vagina. Swimming and bathing are not contraindicated during pregnancy. However, in the third trimester, a patient may have impaired balance and is at risk for a fall.
Dental Care
There may be gum hypertrophy and gingival bleeding during pregnancy. Interdental papillae (epulis) may form in the upper gingiva and may have to be surgically removed. Normal dental procedures such as prophylaxis (cleaning), cavity restoration (filling), and periodontal restoration may be performed under local anesthesia. Antibiotics may be given for dental abscesses. Periodontal disease has been associated with an increased risk of preterm delivery in some studies.
Douching
Douching, which is seldom necessary, may be harmful during pregnancy and should be avoided.
Drugs, Nicotine, & Alcohol
1. Drugs—A teratogen is a toxin, drug, or a biologic agent that causes a harmful effect on a fetus. The US Food and Drug Administration has a classification system for drugs during pregnancy and lactation. The greatest effect of a drug is normally during the period of organogenesis (weeks 2–10 after LNMP). Drugs with the potential for addiction such as heroin, methadone, and benzodiazepines can cause major problems for the neonate, including withdrawal.
2. Nicotine & cigarette smoking—There is an increased risk of low-birth-weight infants with cigarette smoking by pregnant women. Smoking during pregnancy is associated with an increased risk of intrauterine growth restriction, placenta previa, placenta abruption, preterm birth, low birth weight, and perinatal mortality. Pregnant women should be urged not to smoke; but, if cessation is not possible, a reduction of the number of cigarettes smoked per day is encouraged. Pharmacologic agents may be offered to assist with smoking cessation.
3. Alcohol—The precise level of alcohol consumption that is safe during pregnancy cannot be determined. A fetal alcohol syndrome (FAS) after maternal ingestion (>2 oz daily) has been described, with an incidence from 1 in 600 to 1 in 1500 live births. The major features of FAS include pre- and postnatal growth restriction, cranial–facial dysmorphology (including microcephalus and microphthalmia), mental retardation, cardiac defects, and behavioral abnormalities. Infants whose mothers consume alcohol during pregnancy can have FAS or fetal alcohol effects (FAEs) or be normal. Pregnant women should be encouraged to avoid alcohol during pregnancy.
Exercise
Pregnant women should incorporate 30 minutes or more of moderate-intensity physical activity. Activities with risk of maternal injury, especially abdominal trauma, should be avoided. Aerobic and exercise classes have been designed for pregnant women. Pregnancy yoga classes are also available for women. Routines in yoga classes are designed for flexibility and joint protection.
Immunization
Killed virus, toxoid, or recombinant vaccines may be given during pregnancy. The American College of Obstetrics and Gynecology recommends that all pregnant women should receive the injectable influenza vaccine during the season (October–March). The “flu shot” is safe when given in any trimester. Furthermore, if administered during pregnancy, the vaccine appears to reduce the risk of infant respiratory disease within the first 6 months of life. Diphtheria and tetanus toxoid, hepatitis B vaccine series, and killed polio vaccine may be administered during pregnancy to women at risk.
Live attenuated vaccines (varicella, measles, mumps, polio, and rubella) should be given 3 months before pregnancy or postpartum. Live virus vaccines are contra-indicated in pregnancy secondary to the potential risk of fetal infection. Viral shedding occurs in children receiving vaccination, but they do not transmit the virus; consequently, vaccination may be safely given to the children of pregnant women.
Secondary prophylaxis with immune globulin is recommended for pregnant women exposed to measles, hepatitis A, hepatitis B, tetanus, chicken pox, or rabies.
Intercourse
No adverse outcome can be directly attributed to sexual intercourse during pregnancy. If cramping, spotting, or bright red bleeding follows coitus, sexual activity should not occur until the patient is evaluated by her clinician. A patient with preterm labor or vaginal bleeding should not have coitus until evaluated by her clinician.
Nutritional Requirements
The mother’s nutrition from the moment of conception is an important factor in the development of the infant’s metabolic pathways and future well-being. The pregnant woman should be encouraged to eat a balanced diet and should be made aware of special needs for iron, folic acid, calcium, and zinc. The average woman weighing 58 kg (127 lb) has a normal dietary intake of 2300 kcal/d. An additional 300 kcal/d is needed during pregnancy, and an additional 500 kcal/d is needed during breastfeeding (Table 6–1). Consumption of fewer calories could result in inadequate intake of essential nutrients.
Table 6-1. Recommended daily dietary intake for nonpregnant, pregnant, and lactating women.
A. Protein
Protein needs in pregnancy are 1 g per kilogram per day plus 20 g per day in the second half of pregnancy (60–80 g per day for the average woman). Protein intake is crucial for embryonic development, and consumption of lean animal foods (chicken or fish), low-fat dairy products, and vegetable proteins such as legumes should be encouraged.
B. Calcium
Calcium intake should be 1200 mg per day during pregnancy and lactation. Calcium intake is of special concern for the pregnant adolescent and lactating woman. Low calcium intake is defined as less than 600 mg per day; should calcium intake be deficient during pregnancy, demineralization of the maternal skeleton may occur.
C. Iron
Every pregnant woman should have adequate iron intake for the increased red blood cell production that starts at approximately 6 weeks’ gestation. In addition, women should have supplementation of 30 g per day of elemental iron during the second and third trimester. If iron deficiency anemia is diagnosed, the elemental iron dose may be increased to 60–120 mg per day.
D. Vitamins/Minerals
A well-balanced diet is critical to the nutrition of any pregnant woman. Folic acid has been shown to reduce the risk of neural tube defects (NTDs). A daily dose of 4 mg of folic acid is recommended for patients who have had a previous pregnancy affected by an NTD. Folic acid should be initiated a minimum of 1 month before conception and continued for the first 3 months after pregnancy. The recurrence risk of NTD is reduced by 70% with prenatal use of folic acid.
For all other women, a daily intake of at least 0.4 mg of folic acid before conception and through the first 3 months of pregnancy is recommended. Patients with insulin-dependent diabetes mellitus and those with seizure disorders treated with valproic acid and carbamazepine are at increased risk of an NTD (1%) and should receive at least 1 mg per day of folic acid. Vitamin B12 supplements are also desirable for strict vegetarian patients as well as those with megaloblastic anemia.
Travel
Travel (by automobile, train, or plane) does not adversely affect a pregnancy, but separation from the physician may be of concern.
Preparation for Labor
As term approaches, the patient must be instructed on the physiologic changes associated with labor. She is usually admitted to the hospital when contractions occur at 5- to 10-minute intervals. She should be told to seek medical advice for any of the following danger signals: (1) rupture of membranes, (2) vaginal bleeding, (3) decreased fetal movement, (4) evidence of preeclampsia (eg, marked swelling of the hands and face, blurring of vision, headache, epigastric pain, convulsions), (5) chills or fever, (6) severe or unusual abdominal or back pain, or (7) any other severe medical problems.
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