Study on the Thyroid Function of Neonate Born to Mother with Hyperthyroidism

Shin, Choong Ho; Kim, Se Young; Yang, Sei Won; Choi, Jung Hwan; Yun, Chong Ku

Abstract

PURPOSE: In newborns from mothers with Graves' disease, neonatal transient hyperthyroidism or hypothyroidism may develop early in life. We evaluated the incidence and prognosis of neonatal thyroid dysfunction in neonates born to mothers with hyperthyroidism during pregnancy.
METHODS
We measured blood T4, T3, TSH levels and TSH-R-Ab titer in 48 hyperthyroid mothers and their babies between 1988 and 1994.
RESULTS
The mean birth weight was 3.21+/-0.49kg and gestational age was 39+5 weeks and three neonates(6%) were small for gestational age and two(4%) were premature whose mother had hyperthyroidism during pregnancy. Eight of the neonates showed high levels of thyroid hormone and four showed low levels of thyroid hormone but none had symptom or sign. The neonatal thyroid function was not affected by maternal antithyroid medication and maternal TSH-R-Ab level. The positive rate of TSH-R-Ab was 44 percent in neonates. In the neonates with low T4 level, the mean TSH-R-Ab was 38.1+/-19.6%, which was higher than those in euthyroid(14.7+/-9.7%) or hyperthyroid(8.4+/-6.2%) neonates(p<0.05). The neonatal blood TSH-R-Ab levels was correlated with maternal TSH-R-Ab levels(r=0.50, p<0.05). Neonatal T4 didn't show any correlation with maternal TSH-R-Ab but showed negative correlation with neonatal TSH-R-Ab(r=-0.43, p<0.05). Neonates with high T4 showed normal thyroid function within 35 days(10-54days) in average. Neonates with low T4 showed normal thyroid function within 29 days(7-61days) in average. One of neonate with low T4 was given thyroid hormone for 1 month. No one with initial abnoraml thyroid function showed clinical problem through follow-up.
CONCLUSIONS
It is likely that hyperthyroid mothers have more tendency of small babies for gestational age or premature babies. Neonates born to hyperthyroid mothers should be closely monitored because of possible abnormal thyroid function, as shown by this study. It is likely that TSH-R-Ab from hyperthyroid mother usually consists of blocking antibody, rather than stimulating antibody, which might cause hypothyroidism in the neonates.