The literature suggests that up to 19% of umbilical cord blood samples are invalid. Accordingly, it has been proposed that blood should be universally collected from both vessels. We prospectively collected paired arterial and venous blood to examine whether our centre, where staff were experienced in single vessel collection, was more accurate. Of 289 paired samples, 53 (18.3%) were considered invalid. Despite this significant error rate, we propose that routinely, only arterial sampling is needed and that an additional venous sample need only be taken to validate samples in cases of pH < 7.15, a difficult delivery or a non-vigorous baby.

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 ¼ 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 log 10 activin A (r ¼ À 0.01; P ¼ 0.68). Compared with healthy controls, there was no difference in arterial activin A in neonates identified as having suffered significant intrapartum asphyxia ( P ¼ 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 ¼ 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.