Dr. Jeff Hersh: Late-stage pregnancy concerns

Q: My water broke early during my last pregnancy and the doctors induced labor. I am 37 weeks pregnant now; if my water breaks early again should I get induced, or is it better to let things progress naturally?

A: Amniotic fluid, held inside the uterus by the fetal membranes (essentially a sac to contain the fluid), surrounds and protects the developing fetus. The membranes must rupture to allow the fetus to be born.

Premature rupture of the membranes is when they rupture prior to the onset of labor. If this occurs in a preterm pregnancy (prior to 37 weeks gestation) it is termed preterm premature rupture of the membranes. I will discuss the simpler event of premature rupture of the membranes in a full-term pregnancy (over 37 weeks gestation) in today's column.

Although the cause is unknown, premature rupture of the membranes is very common, occurring in about 10 percent of all full-term pregnancies. Once the protective barrier (the intact membranes and amniotic fluid) is compromised, bacteria from the vaginal vault can invade the uterus, increasing the risk of infection for the baby (neonatal sepsis) as well as the mom (chorioamnionitis and/or endometritis). The longer the membranes are ruptured, the greater the risk.

Premature rupture also carries a higher risk of placenta abruptia (where the placental lining separates from the uterus, often causing severe bleeding and increasing the risk of fetal demise) and umbilical cord compression, requiring a cesarean section.

Although it is frequently obvious based on clinical grounds alone, it is often prudent to verify that the membranes have actually ruptured. The amniotic fluid has a neutral pH (7 to 7.5) whereas the vaginal secretions are acidic, so checking the fluid pH (the nitrazine test) can verify the rupture. Microscopic evaluation of dried amniotic fluid can reveal certain characteristics (ferning) and hence also help verify it. After premature rupture of the membranes is confirmed, fetal gestational age and well-being are often evaluated by ultrasound.

Labor often begins spontaneously after rupture; within 24 hours over 70 percent of the time, and within 48 to 72 hours 85 percent to 95 percent of the time.

Induction is when medications are given to stimulate the onset of labor and is very common, being used in 1 of every 5 pregnancies in the U.S. Induction also increases certain risks (possibly because of the increased force of the contractions), including the risk of shoulder dystocia of the infant, increased need for cesarean sections due to fetal distress and increased need for forceps or vacuum delivery. If used just for convenience - to have the birth occur at a more convenient day or time - these risks are not balanced by any medical benefits.

However when used as a medical indication, the risks must be weighed against the benefits. When considering induction for premature rupture of the membranes, there are many factors to consider:

- Antibiotic therapy may lower the rate of maternal infection (although it has not been shown to significantly decrease the rate of neonatal infection).

- Up to 10 percent of premature rupture of the membranes may have the rupture spontaneously "re-seal."

- Over 70 percent of pregnancies enter labor spontaneously within 24 hours of premature rupture of the membranes.

- The risk of infection increases with the duration of the premature rupture of the membranes prior to labor and delivery.

It is uncommon for clinical trials to be conducted with pregnant women as subjects, so the direct data looking at induction as a treatment is limited. One fairly large study from the mid-1990s found that induction for premature rupture of the membranes decreased the risk of maternal infection and the need for neonatal intensive care unit admission for the newborn baby as compared to no induction. There was no significant difference in the (thankfully) low risk of neonatal infection, and no significant difference in the need for a cesarean section.

There have been other small studies which have had similar conclusions, and some studies have also noted that induction with intravenous oxytocin is more effective than "ripening" of the cervix with prostaglandin gel.

Induction has the potential to decrease some of the risks from premature rupture of the membranes, but it carries its own risks as well. The woman's preference of whether she wants to be induced or not is another extremely important factor. The specifics of when and if induction should begin is a decision best made on a case by case basis after detailed discussion between the woman and her health care provider.

Massachusetts-based Jeff Hersh, Ph.D., M.D., F.A.A.P., F.A.C.P., F.A.A.E.P., can be reached at DrHersh@juno.com.