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Umbilical vein oxygen tension independent from gestational age at birth

Umbilical venous oxygen tension (UVPO2) and gestational age are negatively correlated antepartum. To see if the negative correlation between UVPO2 and gestational age would still be present postpartum, a retrospective study of all 7522 births at the University of Zurich Hospital from 1989 through 1992 was performed. The 6612 infants with UVPO2 values were divided into low and higher risk groups. Singletons between the 10th and 90th weight percentiles, born vaginally with cephalic presentation after spontaneous onset of labor from healthy mothers were considered low risk. All other births were considered higher risk. No correlations between UVPO2 and gestational age were found in any group studied (low risk, higher risk or total population). The higher risk group had a lower mean UVPO2 than the low risk group (p < .0001). Since there is a negative correlation before birth and none after birth, this indicates that some preterm infants may be subject to greater drops in UVPO2 during delivery than term infants. The magnitude of the drop increases with additional complications and immaturity. However, not all preterms have normal UVPO2 values for gestational age antepartum. Some preterms already have a low UVPO2 in utero and experience a drop in UVPO2 during delivery as well.