Oxytocin induction and neonatal hyperbilirubinaemia

Intrapartum infusion of aqueous glucose solution, transplacental hyponatraemia and risk of neonatal jaundice

Cord serum sodium levels in three groups of 278 singleton infants, born vaginally at term, were correlated with the incidence of jaundice (serum bilirubin greater than or equal to 85 mumol/1) in the first 3 days of life. Of the 278 infants, 87 were born to mothers who were given infusions of 5% or 10% glucose in water during labour (group I), 90 were born to mothers who received glucose solution as a vehicle for oxytocin (group II), and 101 to mothers who did not receive any intravenous fluid therapy (control group). Jaundice was seen significantly more frequently in groups I (28/87, 32%) and II infants (30/90, 33%) than in the control group (12/101, 12%) (P less than 0.01), but when analysed in relation to cord serum sodium levels, the prevalence of jaundice in the normonatraemic infants (serum sodium greater than or equal to 131 mmol/1) was similar in the three groups. On the other hand, in groups I and II jaundice occurred about 3.5 times more frequently in the hyponatraemic infants [group I (17/32, 53%) and II (20/39, 51%)] than in the normonatraemic infants (P less than 0.01). The difference was not associated with any other perinatal or neonatal characteristic.

Pathogenesis of neonatal hyperbilirubinaemia after induction of labour with oxytocin

To determine the pathogenesis of neonatal hyperbilirubinaemia after oxytocin-induced labour venous cord blood from 95 healthy newborn infants was examined. Of these, 15 were delivered by elective caesarean section, 40 after spontaneous labour, and 40 after oxytocin-induced labour. There was no significant difference in any haematological or biochemical variable between the first two groups. Infants born after oxytocin-induced labour, however, showed clear evidence of increased haemolysis associated with significantly decreased erythrocyte deformability (P less than 0.001). In-vitro studies showed a time- and dose-related reduction in erythrocyte deformability in response to oxytocin. The findings suggest that the vasopressin-like action of oxytocin causes osmotic swelling of erythrocytes leading to decreased deformability and hence more rapid destruction with resultant hyperbilirubinaemia in the neonate.

Pathogenesis of oxytocin-induced neonatal hyperbilirubinaemia

100 term (gestation at least 37 weeks), vertex presenting, vaginally delivered, and fetomaternal blood-group-compatible neonates were studied to evaluate the pathogenesis of neonatal hyperbilirubinaemia induced by oxytocin. 50 infants were born after oxytocin infusion for augmentation of labour and the other 50 were delivered spontaneously. The babies born after oxytocin induction of labour attained significantly higher serum bilirubin levels at age 72 +/- 12 hours than the controls. Infants born after oxytocin showed significant hyponatraemia, hypo-osmolality, and enhanced osmotic fragility of erythrocytes at birth. These biochemical and physiological alterations can be explained by the antidiuretic effects of oxytocin and concomitant administration of large quantities of electrolyte-free dextrose solutions used to administer it. Our observations suggest that cord serum sodium and/or osmolality should be estimated and infants with serum sodium less than 125 mmol/l and/or osmolality less than 260 mmol/kg should be considered for prophylactic administration of phenobarbitone.

Factors influencing the incidence of neonatal jaundice

A retrospective study of 12 461 single births confirmed an association between maternal oxytocin infusion and neonatal jaundice. The effect of oxytocin on jaundice was independent of gestational age at birth, sex, race, epidural anaesthesia, method of delivery, and birth weight, each of which was significantly associated with neonatal jaundice. The effect of oxytocin was, however, small, producing a calculated mean increase in peak plasma bilirubin concentration of 8.6 mumol/1 (0.5 mg/100 ml); this excess was independent of sex and less than the effect of the baby being born one week earlier.