MINNEAPOLIS – Shifting the timing of elective repeat cesareans to late term may have the unintended consequence of increasing the proportion of women needing an emergency cesarean section, results of a new study suggest.
Moreover, these emergency deliveries were associated with a twofold increased risk of adverse maternal and neonatal outcomes after adjustment for confounders, Jennifer Hutcheon, Ph.D., said at the annual meeting of the Society for Pediatric and Perinatal Epidemiologic Research.
Patrice Wendling/IMNG Medical Media
Dr. Jennifer Hutcheon
Previous studies have established that elective repeat cesarean sections performed at early-term gestation, 37-38 weeks, have higher rates of neonatal respiratory complications than late-term deliveries at 39-41 weeks.
The American College of Obstetricians and Gynecologists (ACOG) discourages elective cesarean delivery before 39 weeks of gestation unless there is evidence of fetal lung maturity.
A recent report from the United States and a report from the Netherlands, however, indicate that 35%-55% of elective repeat cesarean deliveries are performed before 39 weeks, said Dr. Hutcheon, an epidemiologist in obstetrics and gynecology at the University of British Columbia, Vancouver.
"A better understanding of potential risks and their mechanisms is needed in order to make sure we implement preventive measures," she said.
To explore this, the researchers used the birth records of 9,206 low-risk women undergoing a planned repeat cesarean delivery in the British Columbia Perinatal Database Registry for 2008-2011, and calculated the correlation between institutional rates of early-term delivery and rates of emergency cesarean delivery for each of the 13 major obstetrical centers in British Columbia. Early term was defined as 37 weeks, 0 days, to 38 weeks, 6 days.
Adverse maternal outcome was defined as any occurrence of maternal mortality, cardiac arrest, obstetric shock, postpartum hemorrhage requiring transfusion or hysterectomy, mechanical ventilation through endotracheal tube, or severe medical morbidity. Adverse neonatal outcome was defined as any in-hospital newborn death, neonatal seizures, or respiratory morbidity requiring positive-pressure ventilation.
The analysis excluded women with suspected intrauterine growth restriction, multiples, congenital anomalies, diabetes, hypertension, or cardiac or renal disease.
In British Columbia, 55% of the elective repeat C-section deliveries were done before 39 weeks, Dr. Hutcheon said. There was considerable variation between institutions, with some centers performing only 35% of cases before 39 weeks and others 72%.
Overall, 15% of repeat cesarean deliveries in the province were performed under emergency timing. Once again, rates ranged between 35% and 72% at the different institutions.
There was a strong negative correlation between institutional rates of early-term delivery and emergency cesareans (r = –0.86; P less than .001), she said. For example, the institution with 72% of its elective repeat cesareans delivered before 39 weeks had fewer than 10% of women needing an emergency cesarean. On the other hand, the institution doing only 35% of elective cesareans before 39 weeks had one in three women going into labor and requiring emergency cesarean delivery.
In a univariate analysis, emergency cesarean delivery was associated with a significantly increased risk of adverse maternal outcome (odds ratio 2.1) and adverse neonatal outcome (OR 2.3), and a modest, nonsignificant increase in obstetrical wound infection (OR 1.4) and use of general anesthesia (OR 1.7), Dr. Hutcheon said.
In a multivariate analysis that adjusted for maternal age, body mass index, number of previous cesareans, and institutional obstetrical volume, the odds ratios were 2.1, 2.5, 1.2, and 1.8, for adverse maternal outcome, adverse neonatal outcome, obstetrical wound infection, and use of general anesthesia, respectively. All differences were significant except for obstetrical wound infection.
Dr. Hutcheon acknowledged that identifying the planned mode of delivery was challenging, and that some of the cesareans performed for an indication of "repeat" or "maternal request/VBAC [vaginal birth after cesarean] declined" may actually have been attempted vaginal deliveries.
To get a handle on this, the investigators looked at the time between hospital admission and when the delivery was actually performed. What they found was that the median interval was less than 3 hours, and was less than 4 hours for all of the cases with adverse outcomes.
"This is certainly more suggestive of a planned cesarean delivery rather than a failed VBAC attempt, where we would expect that interval to be quite a bit longer, although we can’t be sure," she said.
During a discussion of the results, an attendee asked whether it’s possible from the data to identify a "gestational sweet spot" that would reduce the risk of an emergency cesarean and yet be late enough to minimize the risk of adverse neonatal outcomes. Dr. Hutcheon said that is not possible from their data, and that this requires weighing two competing risks.