The hemodynamic effects of maternal hypo- and hyperoxygenation in healthy term pregnancies

OBJECTIVE: To evaluate the hemodynamic effects of maternal hypo- and hyperoxygenation in normal term pregnancy. METHODS: Ten healthy women between 35-41 weeks' gestation were exposed to 10% oxygen in inspired air for 10 minutes and, after a 5-minute recovery period, to a stepwise increase in oxygenation with 50 and 100% oxygen for 10 minutes. Maternal ventilation, hemodynamics, and oxygenation were assessed noninvasively, and maternal and fetal vascular responses were assessed with pulsed-wave color Doppler velocimetry. Computerized cardiotocography was used for fetal heart rate (FHR) analysis. RESULTS: Substantial maternal hypoxia was achieved and accompanied by a statistically significant rise in the maternal heart rate (from 89 +/- 11 to 104 +/- 16 beats per minute) and systolic blood pressure (from 123 +/- 13 to 131 +/- 13 mmHg). Doppler measurements demonstrated a statistically significant decline in the pulsatility index (PI) of the maternal internal carotid artery (from 1.8 +/- 0.3 to 1.5 +/- 0.4) and an increase in the uterine artery PI (from 0.60 +/- 0.12 to 0.72 +/- 0.13). Baseline FHR, heart rate variability, and Doppler velocimetry in the umbilical artery and the middle cerebral artery showed no statistically significant changes. Hyperoxia did not cause changes in the maternal circulation, but the FHR decreased significantly (from 142 +/- 12 to 133 +/- 11 beats per minute). CONCLUSION: Acute short-term hypoxia modifies the maternal circulation, suggesting redistribution of maternal blood flow, but exerts no detectable effects on the healthy fetus. Maternal hyperoxygenation induces no apparent adverse effects.