Fetal activin A: associations with labour, umbilical artery pH and neonatal outcome

Objective To define the ontogeny of umbilical artery activin A at term and to evaluate activin A as a potential marker of perinatal hypoxia. Design A cohort study. Setting A university teaching hospital delivery suite. Population A convenience sample of 141 term pregnancies. Methods At delivery, umbilical artery and vein bloods were collected for blood gas measurements and subsequent measurement of activin A. Activin A levels were correlated with blood gas measurements and with labour and neonatal outcomes. Main outcome measures Umbilical arterial activin A and pH. Results The median (95% CI) umbilical arterial activin A level at delivery was 1.38 (1.34-1.70) ng/mL. Levels varied significantly across gestation (P = 0.03), increasing from 36 to 38 weeks, thereafter decreasing to a nadir at 41 weeks. In 60 matched samples, the median (95% Cl) venous and arterial activin A levels were 0.89 (0.81-1.06) ng/mL and 1.38 (1.21-1.61) ng/mL, respectively (P < 0.0001). Mean umbilical arterial pH was 7.20 (7.06-7.38; 5-95th centiles) and was not significantly correlated with log(10) activin A (r = - 0.01; P = 0.68). Compared with healthy controls, there was no difference in arterial activin A in neonates identified as having suffered significant intrapartum asphyxia (P = 0.96). Fetal activin A levels were significantly lower in cases delivered by emergency caesarean section for complications during the first stage of labour compared with cases delivered vaginally (P = 0.003). Conclusions Umbilical artery activin A does not appear to be a sensitive marker of fetal oxygenation or of risk of hypoxic-ischaemic encephalopathy.