Oral or Poster Presentation
Concurrent Session 3B - Maternal Fetal Medicine
Introduction: We examined associations between gestational age (GA) at birth and cord PO2 values using a large tertiary hospital database, to test the hypothesis that fetal oxygenation will decrease with advancing GA as seen in animal studies, with implications for fetal O2 delivery and consumption.
Methods: Cord PO2 values and other information were obtained for patients delivering at >34 weeks between Jan 1, 1990 and Jun 15, 2011; near-term (NT), 35-36wks, N=3,338; term (T), 37-40wks, N=54,084; post-term (PT), ≥41wks, N=12,430. The effect of GA on cord PO2 (mmHg) was examined in all patients controlling for multiple pregnancy/labor covariates using ANCOVA, and in a subset of low-risk patients. Data are presented as means ± SD; *p<.05 and **p<.01 vs NT values.
Results: For all patients, umbilical vein PO2 increased from 27.1±7.2 in the NTs, to 27.5±6.8* and 27.8±6.6** in the Ts and PTs, respectively; while umbilical artery PO2 decreased from 16.7±5.8 in the NTs, to 15.4±5.5** and 14.6±5.4** in the Ts and PTs, respectively. The low-risk patients showed similar changes with umbilical vein PO2 unchanged at 28.1±6.6 and 28.1±6.4 in the NTs and Ts, respectively, but increasing to 28.4±6.2 (NS) in the PTs; while umbilical artery PO2 decreased from 18.2±5.4 in the NTs, to 16.0±5.4** and 15.2±5.4** in the Ts and PTs, respectively.
Conclusion: Umbilical vein PO2 increased with advancing GA, indicating that placental O2 delivery to the fetus must also be increasing, likely due to increases in placental blood flow and/or efficiency of O2 diffusion. Conversely, umbilical artery PO2 decreased with advancing GA, indicating that fetal O2 levels must also be decreasing, likely due to increasing O2 consumption relative to delivery. These findings are consistent with those in animal studies with fetal O2 consumption ever “outgrowing” O2 delivery, and thereby with a lowered “oxygen margin of safety” for hypoxic-related events with advancing GA,