Premature Rupture of Membranes

Premature rupture of the membranes (PROM) refers to rupture of membranes prior to the onset of labor or regular uterine contractions. It can occur at term or prior to term, in which case it is designated preterm premature rupture of the membranes (PPROM). The frequencies of term, preterm, and midtrimester PROM are 8, 1 to 3, and less than 1 percent of pregnancies, respectively. The incidence of this disorder to be 7-12%. In pregnancies of less than 37 weeks of gestation, preterm birth (and its sequelae) and infection are the major concerns after PROM.

I. Pathophysiology

A. Premature rupture of membranes is defined as rupture of membranes prior to the onset of labor.

B. Preterm premature rupture of membranes is defined as rupture of membranes prior to term.

C. Prolonged rupture of membranes consists of rupture of membranes for more than 24 hours.

D. The latent period is the time interval from rupture of membranes to the onset of regular contractions or labor.

E. Many cases of preterm PROM are caused by idiopathic weakening of the membranes, many of which are caused by subclinical infection. Other causes of PROM include hydramnios, incompetent cervix, abruptio placentae, and amniocentesis.

F. At term, about 8% of patients will present with ruptured membranes prior to the onset of labor.

II. Maternal and neonatal complications

A. Labor usually follows shortly after the occurrence of PROM. Ninety percent of term patients and 50% of preterm patients go into labor within 24 hours after rupture.

B. Patients who do not go into labor immediately are at increasing risk of infection as the duration of rupture increases. Chorioamnionitis, endometritis, sepsis, and neonatal infections may occur.

C. Perinatal risks with preterm PROM are primarily complications from immaturity, including respiratory distress syndrome, intraventricular hemorrhage, patent ductus arteriosus, and necrotizing enterocolitis.

D. Premature gestational age is a more significant cause of neonatal morbidity than is the duration of membrane rupture.

III. Diagnosis of premature rupture of membranes

A. Diagnosis is based on history, physical examination, and laboratory testing. The patient's history alone is correct in 90% of patients. Urinary leakage or excess vaginal discharge is sometimes mistaken for PROM.

B. Sterile speculum exam is the first step in confirming the suspicion of PROM. Digital examination should be avoided because it increases the risk of infection.

1. The general appearance of the cervix should be assessed visually, and prolapse of the umbilical cord or a fetal extremity should be excluded. Cultures for group B streptococcus, gonorrhea, and chlamydia are obtained.

2. A pool of fluid in the posterior vaginal fornix supports the diagnosis of PROM.

3. The presence of amniotic fluid is confirmed by nitrazine testing for an alkaline pH. Amniotic fluid causes nitrazine paper to turn dark blue because the pH is above 6.0-6.5. Nitrazine may be false-positive with contamination from blood, semen, or vaginitis.

4. If pooling and nitrazine are both non-confirmatory, a swab from the posterior fornix should be smeared on a slide, allowed to dry, and examined under a microscope for "ferning," indicating amniotic fluid.

5. Ultrasound examination for oligohydramnios is useful to confirm the diagnosis, but oligohydramnios may be caused by other disorders besides PROM.

C. Laboratory diagnosis

1. Alpha-fetoprotein (AFP) is present at high concentrations in amniotic fluid, but not in vaginal secretions, urine, or semen.

2. Ultrasonography may be of value in the diagnosis of PROM. The finding of anhydramnios or severe oligohydramnios combined with a characteristic history is highly suggestive, but not diagnostic, of rupture of membranes.

3. Gestational age assessment should be calculated. Ultrasonography on admission is useful for determining presentation, residual amniotic fluid volume, fetal size and anatomic survey, and fetal well-being.

4. Assessment of fetal well-being. Fetal well-being is generally assessed via an external fetal monitor. A reactive nonstress test is reassuring. Patients with nonreassuring fetal heart rate testing should be delivered or further evaluated.

IV. Assessment of premature rupture of membranes

A. The gestational age must be carefully assessed. Menstrual history, prenatal exams, and previous sonograms are reviewed. An ultrasound examination should be performed.

B. The patient should be evaluated for the presence of chorioamnionitis [fever (over 38°C), leukocytosis, maternal and fetal tachycardia, uterine tenderness, foul-smelling vaginal discharge].

C. The patient should be evaluated for labor, and a sterile speculum examination should assess cervical change.

D. The fetus should be evaluated with heart rate monitoring because PROM increases the risk of umbilical cord prolapse and fetal distress caused by oligohydramnios.

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