REACTIVITY OF THE HUMAN FETAL PULMONARY CIRCULATION TO MATERNAL HYPEROXYGENATION INCREASES DURING THE 2ND HALF OF PREGNANCY - A RANDOMIZED STUDY

Background-The aims of the present study were to determine whether mat ernal hyperoxygenation affects human fetal pulmonary circulation and w hether there is a gestational age-related response in the fetal pulmon ary circulation to maternal hyperoxygenation during the second half of gestation. Methods and Results-Twenty women between 20 and 26 weeks o f gestation and 20 women between 31 and 36 weeks of gestation with nor mal singleton pregnancies were randomized to receive either 60% humidi fied 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 materna l administration of either 60% oxygen or room air. Left and right vent ricular-cardiac outputs, DA volume blood now, and RPA and LPA volume b lood flows (Q(p)) were calculated. Foramen ovale volume blood flow (le ft ventricular cardiac output-Q(p)) was estimated. Pulsatility index ( PI) values of DA, RPA, LPA, and DPA were calculated. Maternal hyperoxy genation did not change any of the measured fetal parameters between 2 0 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 < .0 001). In addition, Q(p) increased (P < .001), and DA volume blood flow (P < .01) and foramen ovale volume blood now (P < .03) decreased. Lef t and right ventricular cardiac outputs were unchanged. All changes re turned to baseline after maternal hyperoxygenation was discontinued. C onclusions-Reactivity of the human fetal pulmonary circulation to mate rnal hyperoxygenation increases with advancing gestation; this suggest s that fetal pulmonary circulation is under acquired vasoconstriction at least after 31 to 36 weeks of gestation.