Trial of labor after cesarean section in risk pregnancies: A population-based cohort study.

INTRODUCTION: In most pregnancies after a cesarean section, a trial of labor is an option. The objective of the study was to explore trial of labor and its failure in pregnancies with medical risk conditions, in a population with a high trial of labor rate.

MATERIAL AND METHODS: In a cohort study (n = 57 109), using data from the Medical Birth Registry of Norway 1989-2014, women with a second delivery after a first pregnancy cesarean section were included. Preterm, multiple, and non-cephalic deliveries were excluded. The outcomes were trial of labor and failed trial of labor, assessed as rates and relative risk, using deliveries without risk conditions as reference. Temporal trends were assessed by 3-year periods. The exposures were selected medical risk conditions, ie previous offspring death, labor dystocia, diabetes, heart conditions, chronic hypertension, chronic kidney disease, rheumatoid arthritis, thyroid disease, asthma, prepregnancy psychiatric conditions, epilepsy, obesity, gestational diabetes, eclampsia and preeclampsia, gestational hypertension, major malformations, second-pregnancy psychiatric conditions, assisted reproduction, macrosomia, and small-for-gestational-age neonates. Induced onset of labor was compared with spontaneous onset of labor for each condition studied.

RESULTS: In risk pregnancies (n = 31 994) the trial of labor rate was 64.9% and failure rate was 27.6%, compared with 74.6% and 16.4% in pregnancies without any of the risk conditions studied (n = 25 115). The lowest trial of labor rates were observed in diabetes type 1 (49.5%), diabetes type 2 (46.7%), maternal heart conditions (54.5%), and pregnancy-related psychiatric conditions (19.7%). The highest failure rates were observed in diabetes type 1 (43.1%), diabetes type 2 (40.3%), maternal obesity (36.9%), gestational diabetes (36.0%), and offspring macrosomia (43.0%). Induced labor was associated with failed trial of labor (P < .05), whereas after spontaneous labor, failure rates were less than 40% in all conditions studied.

CONCLUSIONS: In conditions with high rates of failed trial of labor, eg diabetes, macrosomia, and obesity, a planned cesarean section might be a better option than a trial of labor, particularly if induction of delivery might be needed.