Influence of intravenous fentanyl on fetal biophysical parameters during labor

The short-acting opioid fentanyl has been shown to be a useful analgesic during labor. The purpose of this prospective, comparative investigation was to determine whether fentanyl influenced fetal biophysical parameters during labor. Twenty-four uncomplicated pregnancies at 37-41 weeks were studied during the early active phase of labor. Those patients who requested analgesia (study group) were given a standard 50-micrograms dose of fentanyl intravenously. The study (N = 12) and control (N = 12) groups were similar in maternal age, parity, and gestational age distribution. Fetal body and breathing movements and heart rate patterns were evaluated continuously for 80 min at 10-min epochs. Unlike the control group, fetuses exposed to fentanyl had fewer body movements between contractions (P < 0.03) and spent less overall time moving (P < 0.02). Breathing was abolished at 10 min postdosing in all fetuses exposed to fentanyl but not in the control group. The FHR beat-to-beat variability was reduced between contractions for the first 30 min in 8 (66%) of study cases and none of the control cases (P < 0.01). A sine wave-like FHR pattern was observed for 30 min in two fetuses exposed to fentanyl. All infants had 1- and 5-minute Apgar scores > 6, an umbilical artery pH > 7.20, and no need for resuscitation. In conclusion, an intravenous dose of fentanyl during early active labor was associated with temporary depressant effects on many fetal biophysical parameters without apparent harm being observed at delivery.