Inductions increase the risk of C-section

It seems rather obvious that medical procedures should be reserved for medical indications. Why? Because almost every medical procedure, even some of the simplest, have small but real risks of complications. And risking complications can only be justified if the medical benefit outweighs the risk.

That rule applies to labor inductions, although many obstetricians have forgotten it. Induction of labor for non-medical reasons, primarily convenience, is attractive, but labor induction is surely a medical procedure. It involves IV administration of a powerful medication as well as intensive monitoring. The complications can include C-section for failed induction, C-section for fetal distress, and rarely even uterine rupture and the death of the baby and the mother.

As childbirth has become ever safer, and as C-sections are so common as to be routine, those risks might seem trivial. A paper published in the current issue of Obstetrics and Gynecology reminds us that they are not. Labor Induction and the Risk of a Cesarean Delivery Among Nulliparous Women at Term, by Ehrenthal et. al. is an important contribution to the scientific literature. The investigators culled the medical records of over 24,000 women who delivered at one large hospital over a period of years. From that group they identified more than 7,804 women having their first baby (nulliparous women) between 37-41 weeks. An astouding 43.6% of women were induced!

… Indications for labor induction as identified by the medical provider were fetal indications in 13.6% of cases, fetal macrosomia in 3.3%, maternal indications in 24.9%, postterm pregnancy less than 41 weeks of completed gestational age in 14.3%, postterm pregnancy 41 or more weeks of gestational age in 18.3%, and 25.6% elective. The overall percentage of elective inductions, if postterm inductions less than 41 weeks were included, was 39.9%…

Since the likelihood that an induction will work is related to the state of readiness of the cervix, the authors were careful to documenent the Bishop score (state of the cervix) for all women.

Among women undergoing labor induction, 40.7% underwent preinduction cervical ripening indicating a Bishop Score less than 6 [an unfavorable cervix]; among women with an elective indication, the proportion was 37%.

These numbers of quite dramatic. More than 43% of women expecting a first baby were induced.Of these nearly 40% were being induced for convenience. More than 1/3 of women undergoing induction for convenience had a cervix that was known to be unfavorable for induction.

The authors looked more closely at the 4,863 women who delivered and had no medical risk factors or pregnancy complications. The overall C-section rate for those women was 25.5%. Being induced doubled the risk of ending up with a C-section, from 13.6% to 25.5%. [note: this section amended to correct percentages that were given incorrectly in the first version].

… Within this low-risk cohort, the risk of cesarean delivery for women with indicated inductions was RR 1.92 (1.61–2.29) and elective inductions was RR 1.84 (1.59 –2.12) when compared with women with spontaneous labor. The odds of cesarean delivery associated with induction for this low-risk group were estimated using logistic regression, and after adjustment for the other risk factors, was adjusted OR 2.03 (1.7–2.4)…

In other words, it was induction itself that increased the risk for C-section, not pregnancy complications or other risk factors. In the case of the indicated inductions the increased risk for C-section is justified by the benefit of reducing perinatal deaths. However, there is no offsetting benefit for inductions without medical indication.

Using a very conservative analysis, the authors estimate that fully 20% of all C-sections done at their institution were the result of inductions for convenience. In other words, if inductions for convenience were banned, the C-section rate would be 20% lower. In their hospital that would mean a reduction in the primary C-section rate for nulliparous women from 25.5% to approximately 20% with no decrease in safety.

As the authors note:

The findings of increased risk related to labor induction are consistent with those from other studies and consistent with findings that labor progression for electively induced labors differs from spontaneous labors, and women with an unfavorable cervix receiving preinduction cervical ripening are those at greatest risk. Multiple studies have found labor induction to be associated with an increased risk among nulliparous, and to a lesser extent multiparous, women…

The take home message is very simple: induction doubles the risk of C-section. That is an acceptable risk when balanced against saving perinatal lives that are threatened by pregnancy complications. It is a totally unacceptable risk when it is undertaken merely for convenience.

Induction of labor is a medical procedure and like all medical procedures, it should be restricted to medical indications. Social inductions should not be allowed. The benefit is trivial and the risk is large.