Prelabor Rupture of the Membranes

What is prelabor rupture of the membranes?

From the Merk Manual - rupture of the membranes 1 hour or more before onset of labor.

When your bag of waters breaks at least an hour before contractions begin, it is considered a premature rupture of the membranes (PROM). It does not matter if the membranes break with a gush or by a small continuous leak. It is all considered PROM. This occurs in about 10% of pregnancies. The nitrazine test used to determine if the bag of waters has broken has a 15% false positive rate - that means if 100 women take the test, 15 will be told their water is broken when it actually is not.

Why is PROM a labor challenge?

In and of itself, the water breaking is not too big of a deal unless it happens before 37 weeks. Before 37 weeks the main concern is to protect the baby by delaying labor as long as safely possible. There are also concerns that a pre-term baby may not be large enough or in the right position to prevent a cord prolapse. The final concern will be maintaining enough fluid in the uterus for the baby's lungs to develop properly.

If you are beyond 37 weeks, the bulk of danger from PROM is gone. Your body replaces the water every three hours, so there is no fear of a "dry birth" even if you leak through your whole labor. However, there are two possible problems that having your bag of waters broken may cause.

First, the bag of waters acts as a defense against bacterial infections for the baby. When the bag of waters is broken, that defense is gone. Studies indicate that the risk of a baby becoming infected increase as the length of time the bag of waters is broken and with each vaginal exam. When your bag of waters has been broken for a certain amount of time (about 18 hours if you are group B strep positive or 24 - 48 hours if you are not), your caregiver will recommend IV antibiotics to reduce the risk of transferring an infection to the baby.

Some caregivers also have a time limit (the 24 hour rule) for how long they are comfortable for your waters to be broken without having active labor contractions. This isn't usually a problem since 70% of women with PROM will give birth within 24 hours. In fact, 90% of the women with PROM will have given birth within 48 hours. Only 2-5% will not have given birth after 72 hours, and that number remains the same even after 7 days. In those cases it is possible the PROM was misdiagnosed or the lead sealed over (however the leak sealing is the exception, not the rule).

Still, becasue the risk for infection increases, most caregivers prefer to get labor over with. Henci Goer reminds us that "When membranes rupture, fluids wash out of the vagina, which means infective bacteria must migrate upstream, against the current, to enter the uterus." Waiting twenty-four hours or even more before inducing labor is safe as long as caregivers keep their fingers and internal monitoring devices out of the vagina - with one possible exception: women who are vaginally colonized by group B streptococci.

The second challenge with PROM is that the fore waters (part of the bag of waters trapped between the baby's head and the cervix when the baby engages in the pelvis) may be broke. Clinically, there is no difference between the breaking of the firewaters or the hind waters. However, it is this fore waters that equalize the pressure on the baby's head to mold and on the cervix to open uniformly. If the fore waters are broken, you may be at a higher risk of developing a cervical lip (meaning that part of your cervix is not as dilated as the rest), and your baby may have marked molding of the head. Babies whose water has broken are more likely to respond to contractions with a dipping heart rate during active labor, possibly because of the greater pressure on their heads.

Both of these situations could challenge your natural birth plans.

Coaching Solutions

Encourage good nutrition during pregnancy to build a strong bag of waters.

If the mother suspects she may have a urinary tract or other infection, encourage her to seek treatment. An existing infection can weaken the bag of waters and encourage a pre-labor break.

If your bag of waters is broken, avoid vaginal exams as these increase the risk for infection.

Things to discuss with your caregiver:

Different caregivers have different protocols for treating PROM. Some will recommend that you go to the hospital right away while others will suggest that you stay home for a while. Some caregivers feel it is important to give antibiotics within 12 hours of the waters breaking, others are comfortable waiting up to 48 hours. Be sure you understand how your caregiver expects to handle this possibility.
Because of the link between vaginal exams, internal monitors and cervical ripening agents to increased risk of infection, your caregiver will probably recommend as few vaginal exams as possible. You may also be limited in options for inducing or augmenting labor and for monitoring if that should become necessary.

References:
Enkin, Keirse, Nilson, Crowther, Duley, Hodnett and Hofmeyr. A guide to effective care in pregnancy and childbirth Third Edition. 2000. Oxford: Oxford University Press.
Goer, Henci. The Thinking Woman's Guide to a Better Birth. 1999. New York: The Berkley Publishing Group.
Althabe, G. Aramburu, R.L. Schwarcz, and R. Caldeyro-Barcia. Influence of the Rupture of Membranes on Compression of the Fetal Head During Labor. Presented by Dr. Althabe, Speical Session, Pan American Conference. June 10, 1969.

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