Obstetric factors associated with cord blood gas values at birth.

Values of pH, base deficit and Pco2 in 885 unselected samples of umbilical blood collected at birth were related to pregnancy and delivery details. An increase in acidosis in both umbilical vein and artery was associated with placental abruption, maternal pethidine, pre-eclampsia, primigravidity, vaginal operative delivery for fetal distress and a long second stage of labour. Increased acidosis in arterial, but not venous, blood occurred with cord entanglement, vaginal breech delivery, postmaturity, high birthweight and a long first stage of labour. The relationship between obstetric factors and the acid-base state of the neonate suggests a possible role for cord blood gas measurements in assessing the results of obstetric practice.