PROM dilemmas: Choosing a strategy, knowing when to call it quits

Midtrimester PROM: 16 to 24 weeks’ gestation

Management differs for each gestational age.

Midtrimester PROM occurs in approximately 0.7% of all pregnancies and is a significant source of morbidity and mortality.^4,5 It may be iatrogenic in nature when it follows an invasive procedure such as amniocentesis or fetoscopy. It also may occur spontaneously, with causes similar to those of PROM at later gestational ages. At this early gestational age, PROM is more likely to be associated with cervical incompetence and inflammation.^6,7

Infection is a risk—and may be the underlying cause

Infection is associated with as many as 30% to 50% of cases of PROM.^4,8-10 Half of the cases of intra-amniotic infection develop within 7 days after PROM. That’s because many cases of early PROM have infection or inflammation as their cause.

Intrauterine demise is common at early gestational ages

The risk of intrauterine fetal demise is inversely related to gestational age at the time of rupture. That is, the earlier the gestational age, the higher the rate of fetal death. One study found that the rate of intrauterine fetal demise was 33% when PROM occurred before 20 weeks’ gestation and 20% when it occurred between 20 and 24 weeks; it was rare after 25 weeks.¹⁰

Pulmonary hypoplasia is more common at this critical juncture

The midtrimester is a critical time for fetal lung development. During the canalicular stage (between 17 and 24 weeks’ gestation), the gas-exchanging acini and pulmonary capillaries are forming, so they are more susceptible to injury. The incidence of pulmonary hypoplasia is approximately 10% when PROM occurs earlier than 20 weeks’ gestation, although a wide range of rates has been reported.^4,8-10 Pulmonary hypoplasia remains a significant cause of neonatal mortality and is found in as many as 77% of autopsies of infants from pregnancies complicated by midtrimester PROM.¹¹

The incidence of pulmonary hypoplasia decreases by as much as 46% with each week of gestational age at the time of PROM.¹² After 26 weeks, when the terminal sac stage of development occurs, the rate of pulmonary hypoplasia complicating PROM drops to less than 2%.^12-14

The degree of oligohydramnios also affects the rate of pulmonary hypoplasia, which increases significantly when the amniotic fluid index is less than 5 cm.¹⁵

Limb deformity may be related to restricted movement

Although limb development occurs in the embryonic period, most limb growth takes place during the second and third trimesters.¹⁶ The restriction in movement and increased pressure associated with prolonged periods of oligohydramnios can lead to skeletal deformity in otherwise normal extremities.

The frequency of deformity varies widely among studies, but the mean incidence is 7%.^4,8-11 A twofold higher incidence of skeletal abnormality occurs when midtrimester PROM is accompanied by severe oligohydramnios. In one study, the rate of skeletal abnormality was 54% when the deepest pocket of amniotic fluid was less than 1 cm, compared with 26% for matched pregnancies with a normal or mildly reduced volume.¹⁶

Maternal complications include retained placenta, endometritis

Maternal complications associated with very early PROM include a higher rate of cesarean section due to fetal malpresentation and FHR abnormalities, which often accompany oligohydramnios and intraamniotic infection.¹⁰ A classical incision is more likely in these cases due to the poorly developed lower uterine segment. Retained placenta necessitating postpartum curettage occurs in 9% to 18% of cases of PROM at less than 20 weeks’ gestation. In addition, postpartum endometritis complicates as many as 40% of cases of midtrimester PROM.^4,8-11

General prognosis

The outcome of midtrimester PROM depends on the underlying cause. If it is iatrogenic, the outcome is usually favorable, with frequent resealing of the membranes; most cases end in a normal term delivery. The outcome of spontaneous PROM is more grim.

Midtrimester PROM has the same relatively short latency (approximately 17 days on average) as PROM that occurs later in pregnancy. Less than 50% of women with midtrimester PROM remain pregnant at the end of the first week, and as many as 75% of these women will have delivered by 28 days after PROM.¹¹ These percentages indicate that most women with midtrimester PROM deliver before fetal viability can be attained, or in the risky periviable period.

Overall, midtrimester PROM is associated with significant fetal, neonatal, and maternal morbidity. The risks must be explained to the patient along with any management plan.

Given the very poor prognosis and small chance of prolonged latency, induction of labor and pregnancy termination are reasonable options at the time of presentation. The patient needs to know that expectant management can be associated with significant long-term morbidity and a higher rate of neonatal mortality.