The American College of Obstetricians and Gynecologists (ACOG) has described examples of commonly accepted indications, contraindications, and clinical conditions requiring special attention for an induction of labor. (See box p. 37.) We must remember that indications for labor induction are often not absolute and need to take maternal and fetal conditions, gestational age, and cervical status into account. Many contraindications are the same as those for either spontaneous labor or vaginal delivery; several obstetric conditions are not contraindications, but do necessitate special attention.
In 1988, the National Center for Health Statistics began requiring hospitals to indicate on birth certificates whether labor was induced or not. This requirement has provided us with remarkable insight into labor induction rates—insight that should cause us to pause, to reflect on available data and our own practices, and to demand that the issue receive more widespread attention.
Over a 10-year period beginning in 1989, the rate of labor induction doubled from about 9% to almost 19% of live births. (See chart.) The trend steadily continued into the new millennium, to the point where, in 2003, nearly 23% of all births involved induction of labor. Clearly, labor induction is one of the most common procedures in obstetrics.
Examining the Increase
The reasons for this significant increase over just 15 years relate to the availability of FDA-approved cervical ripening agents; to both the patient's desire and the physician's convenience; to the acceptance of added risks of cesarean delivery; and to increases in marginal or elective inductions for term pregnancies, especially those past 40 weeks. Inductions in which the reason is not evidence based now account for at least half of all term inductions, or up to 10% of all deliveries. The increase in medically indicated inductions was slower than the overall increase, suggesting that inductions for marginal or elective reasons have risen more rapidly.
Also contributing to the rising rate in inductions is our increasing success with cervical ripening and the fact that, in the current era of ultrasound availability and a more accurate dating of gestational age, we have had to worry less about iatrogenic prematurity.
When considering labor induction, we can view “elective” and “marginal” indications as being very similar, or we can differentiate the two, with “elective” meaning there is no plausible medical or obstetric reason for the induction, and “marginal” referring to cases in which obstetricians face or suspect problems but have no data to suggest that the benefits of labor induction outweigh the risks. I believe it is valuable to consider the terms separately as we attempt to understand the changes in induction rates.
Marginal indications include gestational hypertension; unexplained and mild fetal-growth restriction; idiopathic decreased amniotic fluid (which does not pose substantial danger unless it is accompanied by a recognized complication, such as hypertension or a small-for-gestational-age baby); and a pregnancy beyond 40 weeks. Prospective studies to recommend induction for these and other marginal indications are limited in size or design, or are nonexistent.
There is some rationale behind induction for suspected fetal macrosomia in nondiabetic pregnancies. Theoretically, eliminating further fetal growth should reduce the risks of shoulder dystocia and perhaps of cesarean delivery. However, there is no evidence-based justification for labor induction in these patients. Studies have shown, in fact, that the procedure approximately doubles the cesarean delivery risk, does not reduce neonatal morbidity, and does not appear to reduce the risk of shoulder dystocia.
There is also no published evidence to support the induction of labor for preterm mild preeclampsia, prior shoulder dystocia, and prior cephalopelvic disproportion.
ACOG weighed into the issue by approving “logistic reasons” for labor induction, such as a risk of rapid labor, a patient's unacceptable distance from the hospital, and psychosocial indications. This has left ob.gyns. with a substantial amount of latitude. For instance, one could argue that “psychosocial” reasons could include alleviating the concerns of a mother who previously had a stillborn infant, or alleviating the anxiety of a woman whose spouse is scheduled for deployment to Iraq before the delivery date.
In analyzing the increased rate of labor inductions, we can simply and easily make our own justifications for elective and marginal inductions—we are making our patients happy, for one thing—and put on the back burner the lack of evidence favoring non-medically indicated induction. No matter how appealing our justifications might be, however, we cannot ignore the paucity of published data on benefits, nor can we ignore the data that do exist on the risks of labor induction.