Breaking Waters: Amniotomy or Spontaneous Rupture?

March 19, 2009 at 2:01 am (Hospital Procedures, Informed Consent) (, , , )

One of the myths of childbirth is the idea of a dramatic beginning to labor:  a very pregnant woman is innocently going about her business when all of a sudden: gush-SPLAT!  Her waters break, she is immediately in hard labor, and she is rushed to the hospital.  Sometimes, it is true, labor starts with a tidal wave of breaking waters and intense contractions, but this is the exception, especially for a first-time mother.  The majority (although there are an amazing diversity of variations) of labors are comprised of a gradual buildup of contractions, increasing in intensity and strength.  The most common time for the membranes to break naturally is during the pushing phase, when the waters can act to “slick the slide” (to quote a favorite midwife of mine) and help the baby on down the birth canal.

Since people hold the idea that labors typically start with broken waters, it is understandable that one of the most common and accepted interventions during labor is amniotomy, which is artificial rupture of the membranes (amniotic sac) by a doctor or midwife using an amnihook.  If the membranes haven’t broken on their own, won’t it help  speed things along if a practitioner does it?  This thinking has led to the acceptance of a practice which, when used routinely, may or may not be beneficial, and which does have documented risks to the mother and the fetus.

According to Henci Goer (The Thinking Woman’s Guide to a Better Birth, Perigree, 1999) there are two different types of amniotomy: those done routinely, early in labor, and those done later on for a specific reason.  Let’s look at each type.

The use of amniotomy in early labor is based on the presumption that, when the waters break, it fits the baby’s head tightly into the cervix, allowing contractions to work more effectively to speed dilation and resulting in a shorter labor.  Some studies have shown a shortening of labor by 1-2 hours when this kind of amniotomy was employed (Goer 99).  But before these results influence a mother’s decision about amniotomy, she should ask herself why these labors were shorter, and whether there are any risks resulting from amniotomy that might outweigh the benefit of a possibly shorter labor.

The length of labor described in these studies may be deceptive.  In nine studies of amniotomy vs. “conserving membranes”, Cesarean rates were consistently higher for women whose waters were broken by their practitioner (99).  A Cesarean delivery is usually done before the last minutes of labor, so the length of these labors would have been artificially shortened by the surgery. If amniotomies are more likely to result in a Cesarean section, perhaps it would be prudent to reserve their use until later in labor, when or if an indication arises for which they might be truly beneficial.

Another downside of amniotomy use in early labor is the perception of pain.  Many labor stories (mine included) mention that after the waters break, the pain becomes more intense,  This makes sense, since the amniotic fluid provides a cushion between the mother’s pelvis and the baby’s body.  Once that cushion is removed, the baby exerts more pressure on the mother’s tissues and bones which in some cases can result in more pain. If this happens toward the end of labor, it provides impetus for the mom to push harder and get the baby out.  If it occurs in the beginning of labor, then the process can become more painful at a time when there’s less that the mother can do actively to relieve that pain.  This is not to say that if waters do break naturally or artificially in early labor, it means that the labor will become unmanageably painful.  There are many comfort measures that are quite helpful.  However, if it’s not necessary, why should the mother be subjected to a potentially more painful labor early on unless it’s a natural part of her body’s plan for the birth?

So we see that the supposed benefit of early artificial rupture of membranes might not hold up under scrutiny, and we see that for some mothers there is an elevated experience of pain resulting from amniotomy.  Bur are there any objective, medical risks resulting from amniotomy?  According to Goer, the answer is yes.

As I’ve already mentioned, the amniotic sac provides a cushion around the baby.  When these waters flow out of the womb, the baby is subjected to more of the pressure resulting from contractions.  In extreme cases, the cord can become displaced and pinched, cutting off the baby’s supply of oxygen (cord prolapse).  Even when this doesn’t happen, some babies don’t respond well to the added stress of contractions without the cushioning water.  Their heartrate can become irregular or too slow, and they can descend into fetal distress.  Since these abnormal heart rates are one of the primary causes for Cesarean sections, it makes sense that women who have amniotomies are more likely to have Cesareans than women whose membranes rupture naturally.

Goer also cites several studies that link amniotomy to higher maternal infection rates (101).  Once the waters are broken, the bacteria that are always present in the birth canal can travel up into the womb, precipitating an infection in the mother, the baby, or both.  Vaginal exams, which are frequently performed in the hospital, can hasten this transfer of bacteria.

These risks to mother and/or baby, combined with the questionable nature of the benefits, might lead one to question the necessity of routine early amniotomies.  But what about breaking the waters for a specific reason later in labor?

Sometimes when a mother reaches 7 or more centimeters dilation and then doesn’t progress for a while, a practitioner may recommend amniotomy to remove “bulging forewaters” (a bubble of amniotic sac and fluid that is coming through the cervix before the head).  Again the thinking behind this recommendation is that breaking the waters will help to bring the baby’s head fully onto the cervix, allowing the cervix to dilate more effectively.  In my experience as a doula, I have seen amniotomy in this case to be effective for some mothers.  When labor is already well established, and positions and movement have been tried but haven’t been effective, amniotomy may be helpful to complete dilation and aid the baby’s descent into the birth canal.  However, I think a mother should always check in with her own body and intuition- if she feels like it’s not a good idea, then in the abscence of medical necessity, it’s her right to refuse an amniotomy.  If the mother’s first response is “Yes!  Anything to help move this along!” then it might be a good idea to go ahead with breaking the waters.  Each case of amniotomy at a late stage in labor is individual, and should be evaluated according to the mother’s and practitioner’s judgement.

The risks of late amniotomy are less than those of early amniotomy, because there is less time for the risks to develop.  This is especially true for infection, since the amount of time that passes after the breaking of the waters is a big factor in whether or not an infection will set in.  In regards to fetal distress, it can still occur at a late point in labor, but if the amniotomy is done closer to birth, the baby has less time to become exhausted and depleted.  And if the baby’s head is well engaged, there is less chance of a cord prolapse, although it is still a possibility.

As a doula, my personal birthing philosophy is that bodies are wise, and birth will generally proceed best if left undisturbed by interventions.  However, there are some isolated cases where I’ve seen a late-in-labor amniotomy help a mom to birth her baby more quickly and easily.

Whatever your feelings are about the breaking of your waters, it is a good idea to ask your doctor or midwife about their protocols concerning amniotomy.  As Goer says, “Many caregivers consider amniotomy so trivial that they may not think to advise you that they are about to do one” (102).  If your practitioner does suggest rupturing your membranes during labor, it is entirely reasonable to ask for five minutes to think about the procedure before making up your mind.  This will give you some unpressured time to check in with your body, or read a page in a book, and from there make the decision that is best for you and your baby.

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