Big baby: Is induction of labor necessary?

What’s involved in inducing labor?

Many obstetricians and some midwives recommend inducing labor if you are near or at full-term, and they think the baby is larger than average -- macrosomia, literally, “big body.” Typically, they use an estimation that the baby weighs or will soon weigh 4,000 grams (8 lbs. 13 oz.) as the threshold. Inducing labor usually involves the following:

• Prostaglandin treatment if the cervix is still long, firm, and thick: Prostaglandins are a family of compounds, two of which are known to soften a cervix that isn’t ready for labor. These same two can also stimulate contractions. Prostaglandin E2 is inserted into the vagina either in gel form (Prepidil) or in a tampon (Cervidil). Prostaglandin E1 (Cytotec) comes only as a pill because it is not formulated for the purpose of inducing labor. A piece of the pill may be inserted vaginally or the pill may be given orally.
• Breaking the bag of waters (amniotomy or artificial rupture of membranes): During a vaginal exam, the birth attendant snags and tears the membranes using an instrument that resembles a crochet hook with a small sharp tooth under the curled tip.
• Oxytocin (Pitocin or “Pit”): Pitocin is given intravenously via a pump that controls the dose.

Why would practitioners want to induce labor for suspected big baby?

The theory goes that inducing labor will prevent:

• Cesareans, due to the baby growing too large to fit through the pelvis.
• Shoulder dystocia, a situation where the head is born, but the shoulders hang up behind the pubic bone.
• Birth injuries, namely, broken collar bone, or injury to a complex of nerves controlling the shoulder and arm (brachial plexus injury). Birth injuries often, though not necessarily, occur in conjunction with shoulder dystocia.

However, studies consistently show that inducing labor for suspected big baby accomplishes none of the above (2-3,5,7,9-10,15-16). These studies include two trials, randomly assigning women thought to have big babies either to induction or to await spontaneous labor (7,15). Random assignment trials produce the strongest evidence because they eliminate bias by ensuring that the two groups are truly similar.

Why doesn’t inducing labor help?

Whether a woman carrying a big baby has a cesarean depends largely on her caregiver’s management, not her pelvis. In proof of this, the cesarean rate for babies weighing 4,000 grams or more was three percent in 1958 in Great Britain (4). These days, U.S. obstetricians may perform cesareans on as many as half of women with babies of this size (11,16).

The practitioner’s belief that women cannot safely birth big babies vaginally, or cannot birth them vaginally at all, will lead to cesarean sections. Several studies illustrate this factor at work. Studies have found that:

• C-section rates for mothers having big babies can vary enormously among individual practitioners. One study reported that having a private obstetrician tripled the odds of cesarean compared with having a resident or a midwife (2). Another found rates among obstetricians ranging from less than five percent to one-third (14).
• Doctors may be likely to order planned cesareans for women suspected of carrying big babies. This was true for one-third of the women in one study (3).
• When obstetricians believe that women are carrying a big baby, far more of them may have cesareans than when doctors don’t think the baby is that big, but it actually is. A study reported that half the women whose babies had estimated birth weights of 4,000 grams or more had cesareans versus less than one-third of women with lower estimated birth weights but whose babies were just as big (16).
• The reverse is also true. When ultrasound predicts a big baby, women may be just as likely to have a cesarean when the ultrasound is wrong than when it is right. In yet another study, roughly half the women predicted to have babies with birth weights in the top ten percent had cesareans regardless of whether their babies actually weighed in this range (11).
• Doctors may not give women a fair chance to labor when they think the baby is big. A study found that when obstetricians thought the baby would weigh 4,200 grams (9 lbs. 4 oz.) or more, half the cesareans for poor progress were performed in early labor (16). When they didn’t think the baby was that big, although it was, they performed cesareans for poor progress in early labor less than twenty percent of the time.

Inducing labor for a suspected big baby increases the odds of c-section compared with starting labor on your own. Most, though not all, studies conclude this (2,5,9-10,16). This could be the belief that women can’t, or shouldn’t, birth big babies vaginally coming into play. It could also be the fact that labor induction, even with pretreatment to prepare the cervix, is more likely to end in a cesarean in first-time mothers than starting labor spontaneously.

While shoulder dystocia and birth injuries are more likely in bigger babies, they occur in non-macrosomic babies and occur rarely even in big babies. For this reason, a policy of induction could have little effect on outcomes even if it reduced the incidence of these problems. To give you an idea of the numbers, an analysis of nearly 15,000 births reported shoulder dystocia rates of twelve percent in non-diabetic mothers of babies weighing 4,000 grams or more and one percent in babies weighing less than this. A similar analysis of birth injuries in nearly 20,000 babies found that less than two percent of babies weighing 4,000 grams or more experienced a birth injury as did less than half a percent of smaller babies (8).

Further diminishing any potential benefit, few cases of shoulder dystocia result in injury. In one study, of 825 cases of shoulder dystocia in infants weighing 4,000 grams or more, only thirty-six, four percent, experienced five minute Apgar scores less than 7, a broken bone, or a brachial plexus injury. Of these thirty-six complications, eight were a broken bone. Breaking a bone is not serious because bones heal. Subtracting the eight instances of fracture, only three percent of babies with shoulder dystocia were at risk for long-term consequences. Even so, more than nine out of ten babies with brachial plexus injuries will completely recover as will eighty-eight percent of infants with five minute Apgars of 7 or less (12-13).

What are the potential problems with inducing labor?

While conferring no benefits, inducing labor increases the likelihood of overly strong contractions, fetal distress and, as documented above, probably cesarean section (6).

How might having an induced labor affect your birth experience and postpartum recovery?

Having labor induced will medicalize your experience, in that you will need an IV and continuous electronic fetal monitoring. You will likely be confined to bed for most or all of the labor. Contractions will probably be more painful, so if you wanted to avoid pain medication, this will make it more difficult to achieve that goal. An epidural will help eliminate the pain, but introduces a long list of potential problems of its own. You may run a additional risk of the labor ending in a cesarean, with all that entails in complications, pain, and recovery time.

References

1. Acker DB, Sachs BP, and Friedman EA. Risk factors for shoulder dystocia. Obstet Gynecol 1985;66:762-8.
2. Combs CA, Singh NB, and Khoury JC. Elective induction versus spontaneous labor after sonographic diagnosis of fetal macrosomia. Obstet Gynecol 1993;81(4):492-6.
3. Delpapa EH and Mueller-Heubach E. Pregnancy outcome following ultrasound diagnosis of macrosomia. Obstet Gynecol 1991;78(3):340-3.
4. Francome C and Savage W. Caesarean section in Britain and the United States 12% or 24%: is either the right rate? Soc Sci Med 1993;37(10):1199-218.
5. Friesen CD, Miller AM, and Rayburn WF. Influence of spontaneous or induced labor on delivering the macrosomic fetus. Am J Perinatol 1995;12(1):63-6.
6. Goer H. The Thinking Woman’s Guide to a Better Birth. New York: Perigee Books, 1999.
7. Gonen O et al. Induction of labor versus expectant management in macrosomia: a randomized study. Obstet Gynecol 1997;89(6):913-7.
8. Kolderup LB, Laros RK, and Musci TJ. Incidence of persistent birth injury in macrosomic infants: Am J Obstet Gynecol 1997;177(1):37-41.
9. Larsen JS, Pedersen OD, and Ipsen L. Induction of labor when a large fetus is suspected. Ugeskr Laeger 1991;153(3):181-3.
10. Leaphart WL, Meyer MC, and Capeless EL. Labor induction with a prenatal diagnosis of fetal macrosomia. J Matern Fetal Med 1997;6(2):99-102.
11. Levine AB et al. Sonographic diagnosis of the large for gestational age fetus at term: does it make a difference? Obstet Gynecol 1992;79(1):55-8.
12. Rouse DJ et al. The effectiveness and costs of elective cesarean delivery for fetal macrosomia diagnosed by ultrasound. JAMA 1996;276(18):1480-6.
13. Ruth VJ and Raivio KO. Perinatal brain damage: predictive value of metabolic acidosis and the Apgar score. Br Med J 1988;297:24-7.
14. Sandmire HF and DeMott RK. The Green Bay cesarean section study. IV. The physician factor as a determinant of cesarean birth rates for the large fetus. Am J Obstet Gynecol 1996;174(5):1557-64.
15. Tey A, Eriksen NL, and Blanco JD. A prospective randomized trial of induction versus expectant management in nondiabetic pregnancies with fetal macrosomia. Am J Obstet Gynecol 1995;172(1 Pt 2):293.
16. Weeks JW, Pitman T, and Spinnato JA 2nd. Fetal macrosomia: does antenatal prediction affect delivery route and birth outcome? Am J Obstet Gynecol 1995;173(4):1215-9.