Neonatal thyroid function: influence of perinatal factors

SUMMARY Indices of thyroid function were measured in 229 healthy term neonates at birth and at 5, 10, and 15 days of age. Results were analysed to assess whether maternal diabetes mellitus, toxaemia of pregnancy, intrapartum fetal distress, duration of labour, method of delivery, asphyxia at birth, race, sex, birthweight, birth length, head circumference, or method of feeding influenced any index. Thyroxine, the free thyroxine index, and free thyroxine concentrations at birth correlated with birthweight. Method of delivery influenced mean thyroxine and free thyroxine index values at birth and at age 5 days. Mean values of triiodothyronine, reverse triiodothyronine, thyroxine binding globulin, and thyroid stimulating hormone were not affected by any of the perinatal factors studied. Birthweight and perhaps method of delivery should be taken into account when interpreting neonatal thyroxine parameters but determination of thyroid stimulating hormone as a screen for congenital hypothyroidism in healthy term neonates circumvents these considerations. Thyroid function is in a state of flux during the perinatal period. ' 2 Previous studies3)'1 have documented thyroid hormone, thyroxine binding globulin and thyroid stimulating hormone concen-trations in term and preterm infants at birth, over the neonatal period, and during early infancy. There are, however, very little data available which attempt to evaluate the possible effect of perinatal factors on neonatal thyroid function. " 12 This study aimed to determine whether maternal diabetes mellitus, toxaemia during the third trimester, intra-partum fetal distress, duration of labour, method of delivery, asphyxia at birth; or race, sex, birthweight, birth length, head circumference, and method of feeding influence parameters of thyroid function in healthy term neonates. Subjects and methods Two hundred and twenty nine singleton neonates born between 38 and 42 weeks ' gestation (deter-mined by maternal menstrual history) were studied. Informed maternal consent and approval of th