The Netherlands analysis excluded women with preterm delivery, stillbirth, multiple gestation, transverse position, and breech delivery, as well as women whose deliveries involved both forceps and vacuum and women who had a midline episiotomy.
Factors controlled for in the study included parity, fetal position, birth weight, augmentation with oxytocin, and duration of the second stage of labor.
Dr. van Bavel and all but one of his coinvestigators reported no disclosures.