This chapter deals primarily with APGO Educational Topic Area:
TOPIC 25 PRETERM RUPTURE OF MEMBRANES
Students should be able to list risk factors, possible etiologies, and complications of preterm rupture of membranes. They should be able to outline a basic approach to evaluation and management options, including a description of risks and benefits of expectant management versus immediate delivery. They should understand the role of gestational age in decision making and describe appropriate maternal and fetal monitoring in the setting of preterm rupture of membranes.
Clinical Case
Your patient presents at 28 weeks of gestation complaining of a “gush” of fluid from her vagina while standing at work today. The triage nurse on Labor and Delivery obtains the patient’s vital signs and places the fetal and uterine monitors, then calls you to evaluate the patient. What are your next steps in evaluation? What factors will affect how you manage this patient?
Amniotic fluid is normally produced continuously and, after approximately 16 weeks of gestation, is predominantly dependent on fetal urine production. However, passage of fluid across the fetal membranes, skin, and umbilical cord; fetal saliva production; and fetal pulmonary effluent also contribute. Amniotic fluid protects against infection, fetal trauma, and umbilical cord compression. It also allows for fetal movement and fetal breathing, which, in turn, permits fetal skeletal, chest, and lung development. Decreased or absent amniotic fluid can lead to compression of the umbilical cord and decreased placental blood flow. Disruption (rupture) of the fetal membranes is associated with loss of the protective effects and developmental roles of amniotic fluid.
CLINICAL IMPACT
Premature rupture of membranes ( PROM) is the rupture of the chorioamniotic membrane before the onset of labor. PROM is associated with about 8% of term pregnancies (37 weeks or more of gestational age) and is generally followed by the onset of labor. Preterm PROM (PPROM), defined as PROM that occurs before 37 weeks of gestation, is a leading cause of neonatal morbidity and mortality and is associated with approximately 30% of preterm deliveries. PROM leading to preterm delivery is associated with neonatal complications of prematurity such as respiratory distress syndrome, intraventricular hemorrhage, neonatal infection, necrotizing enterocolitis, neurologic and neuromuscular dysfunction, and sepsis. The major complication of PROM is intrauterine infection. The presence of lower genital tract infections with Neisseria gonorrhoeae and group B streptococcus (GBS) as well as bacterial vaginosis (BV) increases the risk of intrauterine infection associated with PROM. Other complications include prolapsed umbilical cord and abruptio placentae.
Consequences of PPROM depend on the gestational age at the time of occurrence. Midtrimester PPROM (between 16 and 26 weeks of gestational age) complicates about 1% of all pregnancies. PROM that occurs early in pregnancy following midtrimester genetic amniocentesis is very likely to seal with reaccumulation of amniotic fluid. Persistent oligohydramnios at <22 weeks of gestation is associated with incomplete alveolar development and the development of pulmonary hypoplasia. Survival is likely in the 24- to 26-week group, although the morbidities of extreme prematurity in this group of neonates are more substantial. Infants born with pulmonary hypoplasia cannot be adequately ventilated, regardless of the gestational age at birth, and soon succumb to hypoxia and barotrauma from high-pressure ventilation.
ETIOLOGY
The cause of PROM is not clearly understood. Sexually transmitted infections (STIs) and other lower genital tract conditions, such as BV, may play a role, insofar as women with these infections are at higher risk for PROM than those without STI or BV. However, intact fetal membranes and normal amniotic fluid do not fully protect the fetus from infection, because it appears that subclinical intra-amniotic infection may contribute to PROM. Metabolites produced by bacteria and inflammatory mediators may either weaken the fetal membranes or initiate uterine contractions by stimulating prostaglandin synthesis.
Risk Factors
The risk of PROM is at least doubled in women who smoke during pregnancy. Other risk factors for PROM include prior PROM (approximately twofold), short cervical length, prior preterm delivery, polyhydramnios, multiple gestations, and bleeding in early pregnancy (threatened abortion).
Chorioamnionitis
Chorioamnionitis, infection of the fetal membranes and amniotic fluid, poses a major threat to the mother and fetus. Fetal sepsis is associated with an increased risk of morbidity, particularly neurologic abnormalities, such as periventricular leukomalacia and cerebral palsy, secondary to increased inflammatory mediators in the fetal environment. Patients with intra-amniotic infection often experience significant fever (≥100.5°F), tachycardia (maternal and fetal), and uterine tenderness. Purulent cervical discharge is usually a very late finding. The maternal white blood cell (WBC) count is generally elevated, but this finding is nonspecific, and potentially misleading in pregnancy. It may also be the result of antenatal corticosteroid administration. Patients with chorioamnionitis frequently enter spontaneous and often dysfunctional labor. Once the diagnosis of chorioamnionitis is made, treatment consists of intravenous (IV) antibiotic therapy and prompt delivery, by either induction or augmentation of labor, if needed, or cesarean delivery.
DIAGNOSIS
Fluid passing through the vagina must be presumed to be amniotic fluid until proven otherwise. At times, patients describe a “gush” of fluid, whereas at other times they note a history of steady leakage of small amounts of fluid. Intermittent urinary leakage is common during pregnancy, especially near term, and this can be confused with PROM. Likewise, the normally increased vaginal secretions in pregnancy as well as perineal moisture (especially in hot weather) may be mistaken for amniotic fluid.
The differential diagnoses for PROM include urinary incontinence, increased vaginal secretions in pregnancy (physiologic), increased cervical discharge (pathologic, e.g., infection), and exogenous fluids (such as semen or douche).
Nitrazine Test
The nitrazine test uses pH to distinguish amniotic fluid from urine and vaginal secretions. Amniotic fluid is alkaline, having a pH above 7.1; vaginal secretions have a pH of 4.5 to 6.0, and urine has a pH of ≤6.0. To perform the nitrazine test, a sample of fluid obtained from the vagina during a speculum examination is placed on a strip of paper or swab impregnated with nitrazine. If the pH is 7.1 to 7.3, reflecting that of amniotic fluid, the paper or swab turns dark blue. Cervical mucus, blood, and semen are possible causes of false-positive results (Table 17.1).
Fern Test
The fern test is also used to distinguish amniotic fluid from other fluids. It is named for the pattern of arborization that occurs when amniotic fluid is placed on a slide and is allowed to dry in room air. The resultant pattern, which resembles the leaves of a fern plant, is caused by the sodium chloride content of the amniotic fluid. The ferning pattern from amniotic fluid is fine, with multiple branches, as shown in Figure 17.1. Cervical mucus does not typically show ferning, or, if it does, the pattern is thick with much less branching. This test is considered more indicative of ruptured membranes than the nitrazine test, but, as with any test, it is not 100% reliable.
Ultrasonography
Ultrasonography can be helpful in evaluating the possibility of rupture of membranes. If ample amniotic fluid around the fetus is visible on ultrasound examination, the diagnosis of PROM must be questioned. However, if the amount of amniotic fluid leakage is small, sufficient amniotic fluid will still be visible on scan. When there is less than the expected amount of fluid seen on ultrasound, the differential diagnosis of oligohydramnios, including PROM, must be considered. When the clinical history or physical examination is unclear, membrane rupture can be diagnosed unequivocally with ultrasonographically guided transabdominal instillation of indigo carmine dye, followed by observation for passage of blue fluid from the vagina. This procedure is performed very infrequently, however.
FIGURE 17.1. Ferning pattern from amniotic fluid. (Courtesy of Dr. Dwight Rouse. Scott JR, Gibbs RS, Karlan BY, Haney AH. Danforth’s Obstetrics and Gynecology. 9th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2003:40.)
EVALUATION AND MANAGEMENT
Factors to be considered in the management of the patient with PROM include the gestational age at the time of rupture, assessment of fetal well-being, the presence of uterine contractions, the likelihood of chorioamnionitis, the amount of amniotic fluid around the fetus, and the degree of fetal maturity. These management factors, together with the patient’s history, must be carefully evaluated for information relevant to the diagnosis and approach.
Physical Examination
Abdominal examination includes palpation of the uterus for tenderness and fundal height measurement for evaluation of gestational age and fetal lie.
A sterile speculum examination is performed to assess the likelihood of vaginal infection and to obtain cervical or vaginal cultures for N. gonorrhoeae, β-hemolytic streptococcus, and Chlamydia trachomatis.The cervix is visualized for its degree of dilation as well as for the presence of free-flowing amniotic fluid. Fluid is obtained from the vaginal vault for nitrazine and/or fern testing. Because of the risk of infection, digital examination should be kept to a minimum and is best avoided until the patient is in active labor.
Ultrasound examination can be helpful in determining gestational age, verifying the fetal presentation, and assessing the amount of amniotic fluid remaining within the uterine cavity. It has been shown that labor and infection are less likely to occur when an adequate volume of amniotic fluid remains within the uterus.
Term Premature Rupture of Membranes
If PROM occurs at term (≥37 weeks of gestation), spontaneous labor will ensue in 90% of women within about 24 hours. Awaiting the onset of spontaneous labor for 12 to 24 hours is reasonable, unless there are risk factors such as previous or concurrent vaginal infection (such as GBS) or multiple digital pelvic examinations.
However, with informed consent, induction of labor at any time after presentation of a PROM at term is also considered appropriate. The physician should discuss induction versus expectant management, taking into account, in addition to the risk of infection, that oxytocin administration is associated with a decreased risk of chorioamnionitis and endometritis. There appears to be a decrease in the incidence of cesarean delivery in patients managed expectantly. Serial evaluation for the development of intrauterine infection (fever, uterine tenderness, and maternal and/or fetal tachycardia) and other complications of PROM is requisite with expectant management, which, in most cases, should not extend beyond 24 hours in term pregnancy. When the decision to deliver is made, GBS prophylaxis should be given based on prior culture results or risk factors if cultures have not been previously performed.
Preterm Premature Rupture of Membranes
The time from PROM to labor is called the latency period and is inversely related to gestational age. Between 28 weeks and term, about 50% of patients go into labor within 24 hours and 80% within 1 week. Only 50% of patients whose gestational age is 24 to 28 weeks go into labor within 1 week of PROM. It also appears that the more severe the oligohydramnios, the greater the risk of infection and, consequently, the shorter the latency.
Amniocentesis can be helpful in assessing fetal lung maturity (FLM) but can be difficult in the setting of PROM and oligohydramnios. In addition to tests of FLM, evaluation for intra-amniotic infection (using the presence of bacteria on Gram stain, elevated WBC count, low glucose level, or a positive culture) can also be performed. If there is sufficient volume, FLM tests can also be performed on amniotic fluid obtained vaginally.
If there is strong clinical suspicion for the presence of uterine infection, delivery should be effected as soon as possible, regardless of gestational age. If the evaluation suggests intrauterine infection, IV antibiotic therapy and delivery are indicated, regardless of gestational age. The antibiotic prescribed should have a broad spectrum of coverage because of the polymicrobial nature of the infection. The effect of tocolysis to permit antibiotic and antenatal corticosteroid administration in the patient with PPROM who is having contractions has yet to be conclusively evaluated; therefore, specific recommendations for or against tocolysis administration cannot be made. If the gestational age is thought to be in the transitional time of fetal maturity (i.e., from 34 to 36 weeks), the management is variable, depending on individual circumstances (Table 17.2).
32 Weeks to 33 Completed Weeks
Because of the increased risk of chorioamnionitis and because steroids are not recommended after 34 weeks to increase fetal maturity, delivery is recommended when PROM occurs at or beyond 34 weeks of gestation. If PROM occurs at 32 to 33 completed weeks of gestation, the risk of severe complications of prematurity is low if FLM is evident by amniotic fluid samples collected vaginally or by amniocentesis. The efficacy of corticosteroid use at 32 to 33 weeks of gestation has not been specifically addressed for women with PROM, but is recommended by some experts.
24 Weeks to 31 Completed Weeks
If PROM occurs at 24 to 31 completed weeks of gestation, patients should be admitted to the hospital and cared for expectantly, if no maternal or fetal contraindications exist, until 33 completed weeks of gestation. Prophylaxis using antibiotics to prolong latency and a single course of antenatal corticosteroids can help reduce the risks of infection and gestational age–dependent neonatal morbidity. Patients are assessed carefully on a daily basis for uterine tenderness as well as maternal or fetal tachycardia. WBC counts may be obtained and compared with baseline, although the maternal WBC count is, again, nonspecific and can be affected by glucocorticoid administration. Intermittent ultrasound assessment helps to determine amniotic fluid volumes, because leaking of fluid from the vagina may cease and allow amniotic fluid to reaccumulate around the fetus. Daily antepartum testing, such as nonstress tests, can also be helpful to assess fetal well-being. In the absence of sufficient amniotic fluid to buffer the umbilical cord from external pressure, compression of the cord can lead to fetal heart rate decelerations. If the decelerations are repetitive and the fetal heart tracing nonreassuring, there should be early and expeditious delivery to avoid fetal compromise or death. Unfortunately, umbilical cord accidents often are unrecognized for a significant period of time, regardless of the monitoring regimen instituted. Electronic fetal monitoring is used frequently during the initial evaluation period to search for any fetal heart rate decelerations, although the fetal cardiac control mechanisms are often insufficiently developed in preterm fetuses to allow meaningful evaluation for fetal heart rate variability and reactivity.
Midtrimester Preterm Premature Rupture of Membranes
PROM at very early gestational ages (i.e., prior to 24 weeks of gestation) presents additional problems. Along with the risks of prematurity and infection already discussed, the very premature fetus faces the further hazards of pulmonary hypoplasia, skeletal malformations, and other consequences of prolonged oligohydramnios. The relation of PROM with both of these entities is both interesting and important. The inability of the fetus to move freely within the amniotic sac can lead to skeletal contractures, which can become permanent deformities. For normal fetal lung development to occur, fetal breathing must occur. During intrauterine life, the fetus normally inhales and exhales amniotic fluid, with the net movement out into the amniotic fluid space. This adds substances generated in the respiratory tree to the amniotic fluid pool, including the phospholipids that form the basis for many of the fetal maturity tests. If rupture of fetal membranes occurs before 22 weeks of gestation, the lack of amniotic fluid interferes with respiratory efforts and, thus, with sufficient pulmonary development. The result is a failure of normal growth and differentiation of the respiratory tree and fetal chest. If severe, pulmonary hypoplasia may occur, which leads to an inability to maintain ventilation.
Women presenting with PROM before potential viability should be counseled regarding the impact of immediate delivery and the potential risks and benefits of expectant management. Counseling should include a realistic appraisal of neonatal outcomes, including the availability of obstetric monitoring and neonatal intensive care facilities. Because of advances in perinatal care, morbidity and mortality rates continue to decline. An attempt should be made to provide parents with the most up-to-date information possible. Women with previable PPROM are usually managed expectantly, either at home or in the hospital. Once the pregnancy has reached viability, administration of antenatal corticosteroids for fetal maturation is appropriate, given that early delivery remains likely.
Clinical Follow-Up
The sterile speculum examination you performed on your patient was positive for preterm premature rupture of membranes. You further evaluate the mother and fetus to rule out any obvious signs of chorioamnionitis, abruption, or active labor prior to determining whether you will move toward delivery or attempt to prolong the latency period from rupture of membranes to delivery.
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