Factors affecting the increasing incidence of severe non-haemolytic neonatal jaundice

Neonatal hyperbilirubinaemia is increasing in frequency. In view of conflicting evidence about the possible causes, retrospective analyses have been carried out among babies born during six months of 1974. Preliminary analysis confirmed the over-riding importance of preterm birth (before 37 weeks), but only one of 17 such cases could be attributed to ill-judged artificial induction of labor. For the main analysis, the incidence of eight possibly relevant antecedent factors was compared in 46 cases of hyperbilirubinaemia (unconjugated bilirubin more than 15 mg per 100 ml in term babies and more than 13 mg per 100 ml in some preterm babies) and in 92 controls matched for sex and gestational age. Induction of labour by "primary" oxytocin infusion and artificial rupture of the membranes was very significantly more common in the index cases (p less than 0-01), but there was no difference in the incidence of "secondary" oxytocin, used to accelerate spontaneous labour. Evidence of uterin unresponsiveness suggests that the natural onset of labour was being anticipated by at least some days in many of the index cases and this could prevent the natural "priming" of the fetal enzyme systems. An excess of epidural analgesia in the mothers of the index cases was probably due to its association with the need for pain relief during "primary" oxytocin infusions. The higher incidence of postnatal weight loss in the index cases presumably contributed to the hyperbilirubinaemia.