Amniotic fluid pH 7.1–7.3 turns nitrazine paper yellow; >7.3 is blue
Amniotic fluid crystallizes and appears like a fern, identified under microscope
Pooling on speculum exam
Amniotic fluid collects in the posterior vaginal vault
Ultrasonography (not diagnostic)
Oligohydramnios (defined as AFI <5)
Once the diagnosis of PROM is established, the management depends on the gestational age and maturity of the fetus. Important factors include whether or not labor is present and if there is suspected intraamniotic infection. All patients with preterm PROM should be evaluated for intraamniotic infection (chorioamnionitis). Chorioamnionitis occurs when vaginal or cervical bacteria ascend into the amniotic cavity and initiate an inflammation of the chorion and amnion. Risk factors include prolonged labor, PROM, and excessive digital examinations. Chorioamnionitis occurs in 15–25% of women with preterm PROM . The incidence of infection is higher with earlier gestational age . Table 6.2 lists diagnostic criteria for chorioamnionitis
Diagnosis of chorioamnionitis (typically fever plus two other signs)
Maternal signs and symptoms
Fever (>100.4 °F)
Malodorous vaginal discharge
Fetal tachycardia (>160/min)
Decreases in variability on fetal heart rate monitoring
The management of preterm PROM includes administration of antibiotics to reduce neonatal and maternal infections and to prolong the latency period (time from membrane rupture to delivery). There are several antibiotic regimens that have shown benefit. The regimen described by the American College of Obstetricians and Gynecologists (ACOG) in a 2016 practice bulletin is a 7-day antibiotic course starting with intravenous ampicillin (2 g every 6 h) and oral erythromycin (250 mg every 6 h) for 48 h, followed by oral amoxicillin (250 mg every 8 h) and erythromycin base (333 mg every 8 h) . Intrapartum antibiotic prophylaxis against group B streptococcus is also indicated for women with preterm PROM at risk for preterm delivery whose carrier status is unknown.
With regards to fetal lung maturity, a fetus beyond 36 weeks is very likely to have reached lung maturity. In a fetus before 36 weeks, administration of corticosteroids can accelerate lung maturity. Corticosteroids have the additional benefits of reducing neonatal mortality, respiratory distress syndrome, intraventricular hemorrhage, and necrotizing enterocolitis [11–13]. Previous studies have suggested increased risk of infection with administration of corticosteroids in the setting of preterm PROM, but larger studies have not supported these findings. A common regimen is intramuscular betamethasone 12 mg every 24 h for 2 days . Completion of one course of corticosteroids is indicated, irrespective of membrane status, for pregnant women between 24 0/7 weeks and 34 0/7 weeks if there is a concern for premature delivery within 7 days .
Complications associated with preterm PROM include active preterm labor with malpresentation of fetus (breech presentation being the most common), umbilical cord prolapse, infection, fetal distress, and placental abruption (2–5% of pregnancies) . After preterm PROM, infection and umbilical cord accidents contribute to 1–2% of fetal demise . The most significant risks to the fetus after preterm PROM are the myriad of complications of prematurity, the most common being respiratory distress. Additionally, preterm PROM with intrauterine inflammation has been associated with increased risk of impaired neurodevelopment . In approximately 50% of preterm PROM, birth will occur within 1 week . Latency after membrane rupture is inversely correlated to gestational age at rupture of membranes. Obstetric consultation should be obtained early in the ED course of a patient with PROM or preterm PROM. Once fetal viability has been reached (>23 weeks), hospitalization is recommended for patients with PROM and preterm PROM.
Preterm birth is the leading cause of neonatal mortality and one of the most common reasons for hospitalization . In the United States, approximately 12% of all births occur before term, and preterm labor preceded about 50% of these births [20, 21]. Preterm birth accounts for 70% of neonatal deaths and 36% of infant deaths as well as 25–50% of long-term neurologic impairment in children .
Preterm birth is defined as birth between 20 0/7 weeks of gestation and 36 6/7 weeks of gestation. In order to more accurately describe deliveries that occur at or beyond 37 0/7 weeks, new obstetric guidelines have more clearly designated early term as 37 to 38 6/7 weeks and full term as 39 0/7 weeks of gestation through 40 6/7 weeks of gestation . The risk of poor birth outcomes generally decreases with advancing gestational age. The risk is highest for infants born before 34 weeks; however, even infants born between 34 and 37 weeks are more likely to have delivery complications, long-term impairment, and early death than those born later in pregnancy . The risks of perinatal, neonatal, and infant morbidity and mortality are lowest for infants born between 39 0/7 weeks of gestation and 40 6/7 weeks of gestation [24, 25]. Spontaneous preterm birth includes birth that follows preterm labor, preterm PROM, and cervical insufficiency, but does not include indicated preterm delivery for either maternal or fetal condition.
Identifying women who will give birth preterm is an inexact process and can be very challenging as the causes of preterm birth are not well understood. One of the biggest risk factors for preterm birth is a prior preterm birth, which increases a woman’s risk by about twofold . Another risk factor is short cervical length as measured by transvaginal ultrasound . In most studies this is defined by cervix less than 2.5 cm up to 24 weeks gestational age, and in some studies up to 28 weeks . Other risk factors for preterm birth include demographic factors, current pregnancy complications, substance abuse, uterine anomalies, iatrogenic complications, infections, and psychosocial stressors (Table 6.3). Additionally, some studies have linked previous uterine or cervical instrumentation to preterm labor.
Risk factors for preterm birth
Extremes of age (>40 or teenager)
Low socioeconomic status
Substance abuse (tobacco, cocaine)
Prior preterm delivery
Vaginal bleeding in pregnancy
Urinary tract infections
Vaginal infections (bacterial vaginosis)
The diagnosis of preterm labor is usually based on clinical criteria of regular contractions accompanied by cervical dilation, effacement, or both before 37 weeks of gestation. It can also be defined by initial presentation of regular contractions and cervical dilation of at least 2 cm. Less than 10% of women who present with these clinical findings actually give birth within 7 days of presentation . Some of the early maternal signs of preterm labor include increase or change in vaginal discharge, pain from uterine contractions (sometimes reported as lower back pain), pelvic pressure, vaginal bleeding, and leakage of fluid.
Once cervical change and uterine contractions are present, the determination of prematurity is based on patient’s reported LMP or gestational age determined by prior ultrasound. If there was no prenatal care, an ED ultrasound may assist in obtaining an estimated gestational age. In general, a fetus measuring less than 2500 grams on ultrasound is likely to be premature. To differentiate false labor (Braxton Hicks contractions) from true labor, uterine contraction monitoring and repeat cervical exam are used.
Management of Preterm Labor
The initial ED evaluation of a woman with possible premature labor includes urinalysis, complete blood count, type and screen, and ultrasonography. If delivery is not imminent, and an L&D unit is immediately available, these can be completed once the patient is transported. Intravenous hydration with 1–2 L of Lactated Ringers may assist with resolution of irregular contractions, although it is not an effective treatment for true preterm labor. Bed rest is indicated until diagnosis is clear. Additionally, any underlying causes for preterm contractions such as urinary tract infections should be treated.