Reactivity of the human fetal pulmonary circulation to maternal hyperoxygenation increases during the second half of pregnancy: a randomized study.

BACKGROUND The aims of the present study were to determine whether maternal hyperoxygenation affects human fetal pulmonary circulation and whether there is a gestational age-related response in the fetal pulmonary circulation to maternal hyperoxygenation during the second half of gestation. METHODS AND RESULTS Twenty women between 20 and 26 weeks of gestation and 20 women between 31 and 36 weeks of gestation with normal singleton pregnancies were randomized to receive either 60% humidified oxygen or medical compressed air (room air) by a face mask. Fetal aortic and pulmonary valve; ductus arteriosus (DA); and right (RPA), left (LPA), and distal (DPA) pulmonary artery blood velocity waveforms were obtained by Doppler ultrasound before, during, and after maternal administration of either 60% oxygen or room air. Left and right ventricular cardiac outputs, DA volume blood flow, and RPA and LPA volume blood flows (Qp) were calculated. Foramen ovale volume blood flow (left ventricular cardiac output-Qp) was estimated. Pulsatility index (PI) values of DA, RPA, LPA, and DPA were calculated. Maternal hyperoxygenation did not change any of the measured fetal parameters between 20 and 26 weeks, whereas between 31 and 36 weeks, the PI values of RPA, LPA, and DPA decreased (P<.0001) and the PI of DA increased (P<.0001). In addition, Qp increased (P<.001), and DA volume blood flow (P<.01) and foramen ovale volume blood flow (P<.03) decreased. Left and right ventricular cardiac outputs were unchanged. All changes returned to baseline after maternal hyperoxygenation was discontinued. CONCLUSIONS Reactivity of the human fetal pulmonary circulation to maternal hyperoxygenation increases with advancing gestation; this suggests that fetal pulmonary circulation is under acquired vasoconstriction at least after 31 to 36 weeks of gestation.