Premature Rupture of Membranes: Evaluation and Management

EVALUATION AND MANAGEMENT

Factors to be considered in the management of the patient with PROM include the gestational age at the time of rup-ture, assessment of fetal well-being, the presence of uter-ine 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. Abdominal examination includes palpation of the uterus for tenderness and fundal height measurement for evalu-ation 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 strepto-coccus, 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 min-imum 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 assess-ing the amount of amniotic fluid remaining within the uter-ine 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), spon-taneous 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 Group B streptococcus) or multiple digital pelvic examinations.

However, with informed consent, induction of labor at any time after presentation of a PROM at term is also consid-ered appropriate. Information that the physician should share with the patient as this decision is considered includes, in addition to the risk of infection, that oxytocin administra-tion is associated with a decreased risk of chorioamnionitis and endometritis, and that 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 mater-nal 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 preg-nancy. When the decision to deliver is made, group B streptococ-cal 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 latencyperiod and is inversely related to gestational age. Between28 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.

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, evalua-tion for intra-amniotic infection (using the presence of bac-teria on Gram stain, elevated WBC count, low glucose level, or a positive culture) can also be performed. If there is suffi-cient 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 pos-sible, regardless of gestational age.

If the evaluation suggests intrauterine infection, intravenous 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 preterm PROM who is having contractions has yet to be conclusively evaluated; therefore, specific recom-mendations for or against tocolysis administration can-not 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 22.2).

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 amnio-centesis. The efficacy of corticosteroid use at 32 to 33 weeks of ges-tation has not been specifically addressed for women with PROM, but is recommended by some experts.

If PROM occurs at 24 to 31 completed weeks of gesta-tion, patients should be 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 tachy-cardia. WBC counts may be obtained and compared with baseline, although the maternal WBC count is again non-specific and can be affected by glucocorticoid administra-tion. Intermittent ultrasound assessment helps to determine amniotic fluid volumes, because leaking of fluid from the vagina may cease and allow amniotic fluid to re-accumulate around the fetus. Daily fetal movement monitoring by the mother 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 these are frequent and severe, there should be early and expeditious delivery to avoid fetal compromise or death. Unfortunately, such an umbilical cord accident often is unrecognized for a time, regardless of the monitoring regimen instituted. Electronic fetal monitoring is used frequently during the initial evalu-ation period to search for any fetal heart rate decelerations, although the fetal cardiac control mechanisms are often insufficiently developed in preterm fetuses to allow mean-ingful evaluation for fetal heart rate variability and reactivity.

PROM at very early gestational ages, such as before 20 to 22 weeks of gestation, presents additional problems.

Along with the risks of prematurity and infection already discussed, the very premature fetus faces the further haz-ards of pulmonary hypoplasia, skeletal malformations, and other consequences of prolonged oligohydramnios. The relation of PROM with both of these entities is both inter-esting and important. The inability of the fetus to move freely within the amniotic sac can lead to skeletal contrac-tures, which can become permanent deformities. For nor-mal 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 pulmo-nary 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 imme-diate 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, mor-bidity 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 preterm PROM are usually managed expectantly, either at home or in the hospital. Once the pregnancy has reached viabil-ity, administration of antenatal corticosteroids for fetal maturation is appropriate, given that early delivery remains likely.