The effect of maternal oxygenation on cardiopulmonary haemodynamics during the transition at birth in preterm lambs

Background The cardiovascular transition at birth is a period of instability for preterm infants; however, the impact of fetal oxygen (PaO 2 ) levels on this process is unclear. We hypothesized that increasing maternal, and subsequently, fetal oxygenation will increase pulmonary blood flow (PBF) and improve cardiovascular stability at birth. Methods Preterm sheep fetuses (0.9 gestation) were delivered via cesarean section and instrumented to measure carotid pressure and flow, PBF, and cerebral (SctO 2 ) and arterial (SaO 2 ) oxygenation. Ewes were randomized to maternal oxygen supplementation (O 2Supp ; fetal PaO 2 > 20 mmHg, n = 7) or reduction (O 2Red ; PaO 2 < 20 mmHg, n = 8). After reaching target PaO 2 , lambs underwent immediate cord clamping, with ventilation withheld for 1 min, then maintained for 30 min. Results O 2Supp increased fetal pH, PaO 2 , SpO 2 , SctO 2 , and PBF (28.5 ± 7.8 vs 4.0 ± 3.2 mL/min/kg), which was maintained during the period between cord clamping and ventilation. Cord clamping increased blood pressure but reduced oxygenation in O 2Supp lambs. Ventilation caused marked increases in carotid pressure and flow in O 2Red lambs, which were attenuated by prior oxygen supplementation. Conclusions Maternal oxygen supplementation enhances fetal oxygenation and PBF before cord clamping and reduces cardiovascular instability, suggesting potential benefits for improving cardiovascular stability in preterm infants. Impact The impact of maternal and fetal oxygenation on the cardiovascular transition is not known. We found that maternal oxygen supplementation improves fetal oxygen and increases pulmonary blood flow prior to cord clamping. Maternal oxygen supplementation stabilizes carotid blood pressure and flow during cord clamping and ventilation onset. Our findings suggest that maternal oxygen supplementation may provide cardiovascular stability for preterm infants at birth.