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

To define the ontogeny of umbilical artery activin A at term and to evaluate activin A as a potential marker of perinatal hypoxia.

A cohort study.

A university teaching hospital delivery suite.

A convenience sample of 141 term pregnancies.

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.

Umbilical arterial activin A and pH.

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% CI) 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 log10 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).

Umbilical artery activin A does not appear to be a sensitive marker of fetal oxygenation or of risk of hypoxic-ischaemic encephalopathy.