SAN DIEGO – Maternal morbidity was not consistently increased in a study of women with one prior cesarean delivery who were attempting a trial of labor and who were induced between 37 and 40 weeks, according to a secondary analysis of data from the National Institutes of Health Consortium on Safe Labor.
But the risk of admission to the neonatal intensive care unit did increase among women induced at 37 weeks, Dr. Justin Lappen reported at the annual Pregnancy Meeting sponsored by the Society for Maternal-Fetal Medicine.
Further, induction at 37, 38, and 39 weeks of gestation increased the risk of a failed trial of labor after cesarean section (TOLAC) in the 1,626 women in the retrospective multicenter study who were induced, compared with 4,407 who were managed expectantly (odds ratios, 1.53, 1.74, and 2.16, respectively).
The induction group was compared at gestational weeks 37-40 with all undelivered women in the expectant management group. After adjustment for prior spontaneous vaginal delivery, body mass index, hypertensive disorders, maternal age, week of gestation, birth weight, and neonatal gender, induction was not associated with any consistent increase in the risk of maternal morbidity (odds ratios at weeks 37-40 were 0.49, 0.64, 1.87, and 1.06, respectively).
The researchers defined maternal morbidity based on a composite of outcomes including hysterectomy, transfusion, intensive care unit transfer, venous thromboembolism, and death.
The increased risk of the composite maternal morbidity at 39 weeks was primarily the result of a significantly increased risk of transfusion among women with failed TOLAC, said Dr. Lappen of Case Western Reserve University, Cleveland.
However, among those who were induced at 37 weeks, the risk of neonatal ICU admission was increased, compared with women being expectantly managed who delivered at or beyond 37 weeks (OR, 2.51).
No increased risk was seen in those induced beyond 37 weeks, and no increased risk in neonatal morbidity – defined as a composite of 5-minute Apgar scores of less than 5, arterial cord pH less than 7.0, asphyxia, hypoxic ischemic encephalopathy, and death – was seen with induction at any week of gestation analyzed, Dr. Lappen said.
“Our findings should not change the current obstetric practice, which supports an individualized approach to the use of induction in appropriate candidates attempting TOLAC, Dr. Lappen said.
The researchers also performed a subset analysis in a low-risk cohort derived by excluding all women with chronic conditions who were ineligible for expectant management and by limiting the induction group to include only nonmedically indicated inductions of labor.
The association between induction and composite maternal morbidity was unchanged in this subset analysis, with greater risk seen at 39 weeks – again in association with increased risk of transfusion among those with a failed TOLAC attempt.
However, the association between induction and NICU admission at 37 weeks was no longer present in the low-risk cohort, and the risk was cut in half at 39 weeks in this cohort (OR, 0.52). As in the entire cohort, no association between induction and neonatal morbidity was present.
“Consistent with the primary cohort, nonmedically indicated induction was associated with an increased risk of failed TOLAC,” Dr. Lappen said. This finding was statistically significant at 38 and 39 weeks (ORs, 2.67 and 2.34, respectively), he said.
No association was seen between induction and uterine rupture in either the entire cohort or the low-risk cohort, he said.
Study subjects were women with a live, singleton gestation of at least 37 weeks identified from the Consortium on Safe Labor, a cohort of more than 228,600 deliveries at 12 centers between 2002 and 2008, which was designed to characterize current obstetric practice and outcomes.
Dr. Lappen reported having no financial disclosures.