Blood pH in the umbilical artery at birth: An analysis of data from patients delivered in Hesse between 1986 and 1989

Objective: Measuring blood pH in the umbilical artery at birth is an important means of maintaining obstetrical quality. Consideration of the interrelations between low umbilical blood pH and perinatal risk factors may enable obstetricians to provide better care of the mother and child during pregnancy and delivery. We therefore studied the incidence of measuring blood pH at birth, the distribution and normal range of umbilical blood pH at birth, and the correlation between umbilical blood pH and pre-, sub-, and postnatal risk factors in patients delivered in Hesse between 1986 and 1989. Subjects: Over this period 2053 women were delivered between 30 and 32 weeks and 128 654 between 39 and 41 weeks of gestation. Each of these two groups was further subdivided according to the mode of delivery (spontaneous vaginal delivery; operative vaginal delivery; Cesarean section). Of the patients delivered between 39 and 41 weeks of gestation, 24 315 had exhibited no risk factors during pregnancy or delivery. Results: The overall incidence of measuring umbilical blood pH at birth was about 70%, whereas pH measurements were taken in only 60% of preterm babies delivered vaginally. The percentage of preterm neonates with an umbilical blood pH <7.10 was considerably higher than that of term fetuses (5.0% vs. 1.3%). Of the neonates born of women displaying no risk factors during pregnancy and delivery, 22.4% had an umbilical blood pH less than or equal to 7.25. In patients delivered at term hardly any correlation was found between prenatal risk factors and umbilical blood pH. This contrasted to the situation in patients delivered between 30 and 32 weeks of gestation. In most subgroups a close correlation could be demonstrated between umbilical blood pH and both sub- and postnatal risk factors. No correlation was detected between umbilical blood pH and perinatal mortality. Conclusion: In view of the aim of maintaining and improving obstetrical quality in Hesse, the incidence of measuring umbilical blood pH at birth should be increased, especially in preterm fetuses. Since 22.4% of all babies from patients exhibiting no risk factors during pregnancy and delivery had an umbilical blood pH less than or equal to 7.25, we have to reflect once again on the range of 'normal' umbilical blood pH at birth. Consideration of the various interrelations between umbilical blood pH and pre-, sub-, and postnatal risk factors demonstrated in this study may enable obstetricians to reduce the incidence of severely compromised fetuses at birth.