Thyroid function in the newborn in relation to maternal thyroid status during labour in a mild iodine deficiency endemic area in Sudan

Objectives Data on neonatal and maternal thyroid function during labour in a mild iodine deficiency endemic area are lacking. The current study focuse s on elucidating the thyroid function during labour, in a group of pregnant women who live in an area of mild iodine deficiency in Sudan compared to t hat observed in their corresponding newborns. Measurements Serum concentrations of TSH, thyroglobulin (Tg), triiodothyron ine (T3) and free thyroxine (FT4) were investigated during labour in a grou p of mothers and their neonates residing in an area with mild iodine defici ency in Sudan (n = 76 mother-newborn pairs). Design Maternal blood samples were taken on two occasions: first, during th e third trimester of pregnancy (weeks 32-39); and, second, just before deli very. Cord blood samples were obtained by a doctor or a trained midwife dur ing delivery. Results The median concentrations (and interquartile ranges) of neonatal TS H, Tg, T3 and FT4 were 6.8 (4.7-12.4) mU/l, 61 (40.2-98.2) mug/l, 0.9 (0.8- 1.2) nmol/l and 14.2 (13.4-15.9) pmol/l, respectively. The corresponding le vels for the mothers during labour were 2.3 (1.9-3.2) mU/l, 33 (15.0-56.8) mug/l, 2.6 (2.0-2.9) nmol/l and 11.4 (10.3-13.3) pmol/l, respectively. The median neonatal serum concentrations of TSH, Tg and FT4 were significantly higher than the corresponding maternal levels (P < 0.0001, P < 0.0001, P < 0.0001, respectively). In contrast, the median maternal serum concentration of T3 was significantly higher than that of the neonates (P < 0.0001). Whe n the different neonatal thyroid parameters were compared with each other, significant correlations were observed between TSH and FT4 (r = 0.4, P = 0. 001); Tg and T3 (r = -0.3, P = 0.04) and Tg and FT4 (r = 0.5, P = 0.0001). Women with Tg concentrations above 20 mug/l showed a higher median TSH conc entration and lower median FT4 concentration than those with Tg concentrati ons below 20 mug/l (P < 0.001, P < 0.001, respectively). Nevertheless, the thyroid function of neonates born of mothers with elevated Tg was similar t o that of neonates born of mothers with low Tg levels. No significant chang es had occurred in the thyroid function parameters between the third trimes ter of pregnancy and during the time of labour. The thyroid function indica tors of the babies born by vaginal delivery did not differ significantly fr om those of the babies born by Caesarian section. ConclusionsThe study suggests that, in areas with mild iodine deficiency, n eonates may be at the limit of decompensation as evidenced by their enhance d TSH and Tg levels as well as increased T4 compared to their mothers. This finding must not create a false sense of well-being and points rather to t he urgency of iodine supplementation of mothers even in areas with mild iod ine deficiency, as in this part of Sudan. The mode of delivery, whether by spontaneous vaginal delivery or Caesarian section, did not seem to affect t he thyroid function of the newborn.