The fetal membranes protect the baby by forming a barrier to infection within the underwater world of the amniotic sac. The amniotic fluid cushions the baby from the bumps and bruises of the outside world. When the membranes rupture, announcing the imminent arrival of the baby, the delivery will take place within hours or days. Rupturing of the membranes is commonly called "breaking the water."
We do not have a very good understanding yet of exactly how or why the membranes rupture. Although natural rupture of the membranes is more likely as labor progresses and the cervix dilates, in some instances the membranes may rupture shortly before labor begins-even if the cervix has not dilated at all. In fact, in some women, the rupture of the membranes seems to trigger the onset of labor.
In almost every pregnancy, the membranes will rupture naturally at some point before the baby is born. In the rare cases that this does not happen, the membranes should be ruptured artificially. This will prevent the baby from being born in caul, which means the head would be covered by the membranes. If this were to happen, the baby would be unable to draw its first breath because it is still within the sac.
There are other, more common reasons why membranes may be ruptured artificially. The most common is to speed up labor. It is well known that when the membranes rupture during the active phase of labor (either naturally or artificially induced), the contractions often become stronger and more frequent. Sometimes, this is all that is needed to speed up a labor that has been making minimal progress over many hours.
Another common reason to rupture the membranes artificially is if fetal distress is suspected. Rupturing the membranes serves two purposes: First, it allows the practitioner to place an internal electrode on the baby's head to record the fetal heart rate more accurately (see Chapter 18). It also allows the practitioner to determine whether there is any meconium in the amniotic fluid. Meconium is a sticky, green substance that is produced by the fetal intestine; it is the equivalent of a bowel movement. There will be meconium in a newborn's diapers for the first few days of his or her life.
The baby will pass meconium into the amniotic fluid in response to stress (such as oxygen deprivation). A small amount is not harmful, but a moderate to large amount is cause for concern. First, it suggests that the baby may be subject to stress by labor. Second, meconium can get into the baby's lungs, where it could cause breathing problems and even pneumonia after birth. If there is a significant amount of meconium in the amniotic fluid, a pediatrician or anesthesiologist may be asked to attend the birth and examine the newborn immediately, to suction out the meconium before it can be breathed farther into the baby's lungs.
Rupturing the membranes artificially is a very simple procedure. It is done during an ordinary vaginal exam; an amnio-hook, which looks like a large crochet hook, is used to scratch the surface of the membranes. It is painless for both mother and baby.
In many cases, your practitioner will offer you the option of artificial rupture of the membranes. In those instances, it is just a matter of personal preference as to whether you would like it done to speed up your labor. However, this procedure is advisable if the fetal heart rate tracing suggests the possibility of fetal distress. Rupturing the membranes artificially can provide valuable information for taking proper care of your baby.
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