Association of obstetric intervention with temporal patterns of childbirth

To examine the gestational age at and day and time of delivery in current U.S. obstetric practice.

We examined electronic records from 72 hospitals in 16 states during a 4-month period during 2013. Day of week of delivery, time of day of delivery, and route of delivery were examined in various subpopulations delivering both with and without obstetric intervention.

Records of 21,381 women were examined. The distribution curve for gestational age at delivery peaked at 39 weeks both for the entire group and for the subgroup entering labor spontaneously and delivering vaginally without augmentation. Statistical modeling suggests that medical intervention accounts for only a fraction of the shift in distribution peak from 40 to 39 weeks of gestation. Three temporal peaks of total and primary cesarean delivery were seen on weekdays, corresponding to immediate preclinic, lunch time, and immediate postclinic timeframes. These peaks were not seen on weekend days. The risk of nonelective primary cesarean delivery during a weekday was approximately one third higher than on a weekend (relative rate 1.36, confidence interval 1.24-1.49).

The recently described shift in peak distribution of U.S. gestational age at delivery from 40 to 39 weeks of gestation may reflect an underlying physiologic change in the U.S. population and is not exclusively related to obstetric intervention. During the work week, factors other than medical necessity appear to have a marked association with both timing of delivery and rate of cesarean delivery and may affect up to one third of primary cesarean deliveries.