Lectures in Obstetrics, Gynaecology and Women’s Health

20. Antenatal Care

Gab Kovacs¹ and Paula Briggs²

(1)

Department of Obstetrics and Gynaecology, Monash University, Clayton, Victoria, Australia

(2)

Sexual and Reproductive Health, Southport and Ormskirk Hospital, Southport, UK

At the First Visit

Routine Investigations at First Visit

Haematology

Infection Screens

Hormone Tests

Vitamin D

General Advice

Antenatal Visits

Late Pregnancy Foetal Surveillance for IUGR

The Obstetric History and Examination and Antenatal Assessment are discussed in Chap. 5.

The aim of antenatal care is to ensure that the baby is delivered in the best condition, and that any problems are diagnosed as early as possible.

At the First Visit

· Confirm pregnancy and establish the expected date of delivery. This is 9 months and 7 days after the Last Normal Menstrual Period (LNMP) – assuming day 14 ovulation. This is easily calculated: from January to March add 9 months; from April to December take away 3 months; then add 7 days.

This should be confirmed using ultrasound

· Clinical assessment to identify any conditions that may be relevant during the pregnancy

Routine Investigations at First Visit

Haematology

· Full blood count (FBC) including Mean Corpuscular Volume (MCV) and Mean Corpuscular Haemoglobin Concentration (MCHC). If abnormal, haemoglobin electrophoresis should be undertaken to detect thalassaemia.

· Blood group and antibody screen (this includes Rhesus and other minor red blood cell antigens).

Infection Screens

· Rubella immunity- check at the start of each pregnancy

· Varicella immunity –checking is recommended if there is not a definite history of previous infection

· Syphilis serology and HIV

· Hepatitis B and Hepatitis C serology is recommended

· CMV- not performed routinely

· Toxoplasma screening – if indicated

· Chlamydia screening – can be offered

· Midstream urine, microscopy and culture

Hormone Tests

· TSH – uniform screening for subclinical thyroid disease is still controversial

Vitamin D

Women at risk of deficiency should be screened (low exposure to sunlight)

General Advice

· Advice about a healthy diet and sensible weight gain (ideally no more than a pound a week)

· Work plan

· Avoiding smoking and recreational drugs

· Avoiding any non-prescription medications

· Avoid exposure to X-rays and other radiation unless absolutely necessary

· Avoid alcohol if possible

· Exercise during pregnancy is not harmful but contact sports should be avoided

· The risk of listeria is reduced if high risk foods are avoided. These include unpasturised cheeses, uncooked meats, pate and undercooked prepared meals

· Herbal medicines should be avoided as few of these have been proven to be safe and/or effective in pregnancy

· Vitamin and mineral supplementation:

· All women should commence folic acid (400 ug) before conception and this should be continued for the first 12 weeks of the pregnancy. Women who have previously conceived an affected child with neural tube defect (NTD) should be recommended to take 5 mg folic acid daily. This also applies to diabetic women.

· Iron Supplements – should only be offered if iron deficiency is diagnosed (side effects outweigh benefits).

· Vitamin A – Supplementation above 700 ug may be teratogenic and should be avoided.

· Vitamin D – a supplement of 10 ug per day is recommended for all women.

· Iodine 150 ug/day is recommended.

Antenatal Visits

· The aim of these visits is to detect any pregnancy related problems that could be minimised by early intervention

· To undertake a risk analysis in order to compare the risk of delivery (prematurity) against the risk of continuing the pregnancy (to either or both the foetus and mother)

· Routine antenatal examination as described in detail in Chap. 5. Blood pressure measurement and urine testing for protein are essential and carried out at each visit to detect hypertension of pregnancy and pre-eclampsia

· Frequency of visits should be timed to correspond with investigations:

· Ultrasound at 12 weeks to detect neural tube defects. This is undertaken in combination with biochemical testing to screen for aneuploidy.

· Screening for aneuploidy, especially trisomy 21 and trisomy 18, is undertaken to identify women with increased risk. These women are then offered a diagnostic test (amniocentesis, chorionic villus sampling, tertiary ultrasound), with the option of termination of pregnancy if the couple choose.

· Combined first trimester screening involves an ultrasound examination in combination with biochemical tests. The nuchal thickness and crown-rump length (CRL) are measured (when CRL is 45–84 mm corresponding to between 11 and 13 weeks 6 days). Biochemical analysis of maternal blood for Pregnancy Associated Placental Protein (PAPP-A) and Free β hCG is analysed. This information together with maternal age is analysed on a computer program using Fetal Medicine Foundation (FMF) software. The risk is then calculated as 1:X. A ratio higher than 1:300 is considered “increased”, and confirmatory tests are indicated, ie CVS or amniocentesis, where the karyotype can be confirmed.

· Non Invasive Prenatal Testing (NIPT) has recently become available. Women have a blood test after 10 weeks gestation which is analysed for cell free DNA, released from the placenta. This can be used to assess the genetic make up of the foetus. This technique has been validated in several clinical trials with an accuracy of 99 % for trisomy 18 and 21, and 80–90 % for trisomy 13.

· A foetal morphology scan is recommended at 18–20 weeks

· Screening for gestational diabetes should be performed at 26–28 weeks gestation. In women at high risk of Gestational Diabetes Mellitus (GDM), earlier screening may be considered, but should be repeated at 26–28 weeks even if the previous test is negative.

· The recommended test is a 2 h 75 g Pregnancy Oral Glucose Tolerance Test (POGTT). Abnormalities are classified as: (Table 20.1)

Table 20.1

Criteria for diagnosing GDM and diabetes mellitus in pregnancy (DMP) (WHO definition)

Diagnosis	Fasting glucose (mmol/l)	I hour after 75 g load (mmol/l)	2 h after 75 g load (mmol/l)
Normal	<5.1	<10.0	<8.5
GDM	5.1–6.9	>10.0	8.5–11.0
DMP	>7.0		>11.1

· Rh antibody measurement for Rh negative women and haemoglobin estimation for all women is undertaken at 28 weeks. For Rh negative women (with no antibodies), prophylactic Anti-D (125 mcg) should be administered routinely at 28 and 34 weeks gestation. It should also be administered if there is antenatal haemorrhage, amniocentesis, or External Cephalic Version (ECV) has been attempted, or any external abdominal trauma.

· The magnitude of any feto-maternal haemorrhage can be estimated using Kleinhauer testing of maternal blood.

· Syphilis, HIV, Hepatitis B and C re-screening is indicated in “high risk” individuals.

· Group B streptococcus (GBS) screening. Local protocols define whether GBS screening is universal, or risk based. Risk factors include labour commencing under 37 weeks, prolonged rupture of the membranes, or maternal fever. Screening should be undertaken at 35–37 weeks with both vaginal and rectal swabs for microscopy and culture.

· In women with previous GBS bacteruria during pregnancy, or previous GBS infection during pregnancy antibiotics should be administered during labour.

· Beyond 28 weeks the growth of the foetus and the quantity of liquor are assessed to detect any intrauterine growth restriction (IUGR). It is recommended that visits should be every 2 weeks until 36 weeks.

Late Pregnancy Foetal Surveillance for IUGR

This should be undertaken if:

· There is clinical suspicion of IUGR on examination

· Poor past obstetric history

· Maternal conditions that can compromise the foetus eg hypertension of pregnancy

· Inability to clinically assess growth eg. maternal obesity

Monitoring includes antepartum foetal monitoring to study the reaction of the foetal heart to Braxton-Hicks contractions (CardioTocoGraphy – CTG).

This can be combined with a “biophysical profile” where ultrasound scanning is undertaken to measure the amniotic fluid volume, foetal body tone, foetal movements and foetal breathing pattern.

The ultimate decision during antenatal care is “when is the baby safer outside than inside” ie. when should it be delivered with either induction of labour or Caesarean section.