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Is “Suspected Big Baby” a Good Reason to Induce Labor?

I was asked recently for some information on induction, specifically if the reason is “suspected big baby.”  The person was asking on behalf of a friend, who was being induced at just a few days past her due date.

Well first, lets start with the medical reasons that the American College of Obstetrics and Gynecology (ACOG) indicate in a patient education brochure that labor should be induced for:

• Pregnancy is postterm (more than 42 weeks).
• High blood pressure caused by your pregnancy.
• Health problems that could harm you or your baby.
• An infection in the uterus.
• Placental abruption (the placenta has begun to separate from the inner wall of the uterus before the baby is born). You may have your baby by cesarean birth in this situation.
• Water is broken

These reasons were affirmed in a June 2009 update by ACOG.  You may note that

• “Post-term” is defined specifically as being beyond 42 weeks, not just a few days after the due date.
•  ”suspected large baby” is not on that list.
• “low amniotic fluid” is not on the list…oh, wait, that’s not an issue here–but it is becoming a more and more common reason that is used to justify induction. 

Why is that?

The first factor is easy.  A woman, especially a first time mother, is NOT over-due yet a few days after her 40 week ”due date.”  In fact, according to a Harvard study, the average healthy first time mother will gestate 41 weeks 1 day.  So in the case of the woman in this situation, she isn’t even truly “due” yet.

The “suspected large baby” reason for inducing labor seems to make more sense though–get the baby out before the baby gets any bigger, right? 

Well, not so fast…for that, we move the American Academy of Family Physicians (AAFP).  In an article that appeared in their professional journal in 2001, we read:

In cases of term patients with suspected fetal macrosomia, current evidence does not support early induction of labor. Results from recent reports indicate that induction of labor at least doubles the risk of cesarean delivery without reducing the risk of shoulder dystocia or newborn morbidity

And

• Labor and vaginal delivery are not contraindicated for women with estimated fetal weights up to 5,000 g (11 lbs) in the absence of maternal diabetes. 

And

• Suspected fetal macrosomia is not a contraindication to attempted vaginal birth after a previous cesarean delivery.

Another article from the AAFP (no longer available on-line) also is helpful in considering this question:

observational studies suggest that induction actually increases the cesarean section rate without favorably altering perinatal outcomes.

One study compared the outcomes of patients in whom macrosomia was suspected before delivery to those in whom it was not. The authors found that the risk of cesarean section was substantially higher (52 versus 30 percent) in pregnancies in which macrosomia was suspected, even after controlling for birth weight and other confounding variables. More importantly, the difference in the cesarean section rate was attributable to a greater proportion of failed inductions for macrosomia in the group in which it was suspected. Another observational study28 compared the outcomes of infants with suspected macrosomia who were managed with induction versus expectantly. Again, the rate of cesarean section was substantially higher (57 versus 31 percent) in the group that underwent elective induction. In addition to these studies, a recent meta-analysis concluded that induction did not decrease the rate of cesarean section, instrumental delivery or perinatal morbidity.

In other words, having a label of “suspected large baby” on you puts you at increased risk of c-section than if the fetal weight had not been known–part of why I advise my clients to avoid ultrasounds for the purpose of predicting fetal weight.  Part of the increased risk is just because of the inherrant risks of induction–fetal distress caused by the increased intensity of Pitocin induced contractions, or inability to complete dilation due to just not be ready to give birth.  But another part of the risk is your care provider’s perception of your ability to deliver vaginally without assistance–if the belief is that you will not be able to deliver without assistance, the care provider will more quickly move to offer interventions to “save you the effort of needless labor.”

A further quote from that article:

The medical literature confirms that prediction of fetal macrosomia is difficult. Ultrasound estimation of fetal weight adds little additional useful information. What clinicians really want to predict is not macrosomia, per se, but the serious complications that physicians mistakenly associate as occurring only with macrosomia, such as brachial plexus injury or shoulder dystocia. Such complications, however, are not determined by birth weight alone, but by a complex and poorly understood relationship between fetal and maternal anatomy and other factors. Moreover, the vast majority of macrosomic infants who are delivered vaginally do very well, even if they experience shoulder dystocia. The weight estimate of the suspected macrosomic fetus should be recognized as uncertain. The patient’s obstetric history, her progress during labor, the adequacy of her pelvis and other evidence suggestive of fetopelvic disproportion should be used in determining an intervention, such as cesarean section.

Simply put, it is hard to predict the weight of the baby prior to birth.  Ultrasounds are notoriously wrong–in fact, I had a client who was told at 40 weeks that her baby was 10 lbs, and when she gave birth at 41 weeks 1 day her baby was 8 lbs 12 oz–which means that the ultrasound was off by 1 lb 13 oz–allowing for 8 oz of growth per week.  To be fair, I also had another client who was told about a week before she birthed that her baby would be about 8 lbs, and her baby turned out to be 9 lbs 11 oz–but she gave birth vaginally–with no tearing, DESPITE the dreaded “shoulder dystocia.”

And further, inducing labor makes for more difficulty in labor because the body is not ready for labor.  The uterus may not respond well to the oxytocin, and fetal distress may result.  Also, during the last few days of pregnancy hormones are released that relax the ligaments in the pelvis, allowing it to open wider for the baby to pass through.  Without the benefit of these hormones, the woman may not be able to birth a baby much smaller than one she may be able to birth when labor is allowed to start spontaneously.

Bottom line…inducing labor for “suspected large baby” is neither medically reccommended by the two major medical societies that handle birth in America (ACOG and AAFP), and it is more likely to result in a difficult birth than waiting for labor to start on its own.

Tags: AAFP, ACOG, Induction, pitocin, suspected big baby, VBAC/Cesarean