Supine position in labor and associated fetal heart rate changes.

Presented is an investigation of the relationship of fetal heart rate (FHR) deceleration and position of the patient in labor. In a group of 902 laboring patients, 126 (14%) demonstrated late decelerations. Of the 126, 24 (19%) patients demonstrated late decelerations in the supine position only. These occurred during uterine contractions and were associated with reduced femoral arterial blood pressure and amplitude of the capillary pulse of the big toe. A drop in capillary blood pH of the fetal scalp could also be demonstrated. These effects reproducibly appeared and disappeared when supine and lateral positions were alternated. These data would suggest that maternal aortic compression by the pregnant uterus plays a role in the etiology of fetal stress as expressed by changes in fetal heart rate and acid base balance. This effect can be evaluated and monitored simply by recording the pulse pressure of the big toe and femoral arterial pressure. These atraumatic procedures can be applied to any patient.