Fetal acidosis in labour: a prospective study on the effect of parity.

The effect of parity on intrapartum fetal scalp pH was investigated in 6466 patients in labour with a live fetus who were delivered in 1987. 350 (5.4%) required fetal scalp blood sampling for pH (FBS), 236 primigravidae (10.4%) and 114 multigravidae (2.7%) (P less than 0.001). Fetal acidosis (pH less than 7.20) was detected in 35 patients, 27 primigravidae (11.4%) and 8 multigravidae (7.0%) (P less than 0.001). The incidence of intrapartum acidosis in the 2275 primigravidae and the 4191 multigravidae was 1.2 and 0.2% respectively (P less than 0.001). The two deaths from birth asphyxia and three cases of neonatal seizures occurred in primigravidae. In primigravidae requiring FBS, fetal acidosis was not associated with the use of oxytocin or with increased duration of labour. Neonatal seizures were more common overall in primigravidae than in multigravidae and more common in patients requiring FBS than in those not requiring FBS (P less than 0.05). The higher incidence of FBS, fetal scalp acidosis and neonatal seizures in primigravidae has important implications for intrapartum fetal monitoring.