ABSTRACT
Objective: To study the dose-response relationship between maternal thyroid hormone levels in the first twenty weeks of pregnancy and the infant physical and neuropsychological development. Methods: In this prospective cohort study, a total of 945 women and their children were included. Maternal serum samples during first half of the pregnancy were collected and analyzed for levels of thyroid hormones by using the electro-chemiluminescence immunoassay. Maternal social demographic information was collected by using the a self-administered questionnaire. Physical measurements of newborns and neuropsychological evaluation of infants were performed by doctors of maternal and child health care. Results: The differences in newborns' birth length and head circumference were significant among the newborns of mothers with different percentiles of maternal serum (thyroid-stimulating hormone, TSH) levels (P<0.05). Newborns with maternal TSH level ≥P(95) or <P(5) had significantly lower birth length and birth head circumference, compared with the newborns with maternal TSH level between P(25)-P(75) (P<0.05). Newborns' birth head circumferences showed an inverted U-shaped association with maternal serum TSH level (Y=33.940+0.003X-0.109X(2), F=4.685, P=0.009). The difference in mental development index (MDI) of the infants at 18-30 months were significant among the infants of mothers with different percentiles of maternal serum TSH level (P<0.05). Infants with maternal TSH level ≥P(90) showed lower MDI (6.39, 95%CI: 2.29-10.49, P=0.002) compared with the infants with maternal TSH level between P(25)-P(75). Infant's MDI at 18- 30 months also showed an inverted U-shaped association with maternal serum TSH level (Y=103.249-1.524X-0.939X(2), F=6.616, P=0.001). Conclusions: Maternal TSH level was associated with newborn's birth length, birth head circumference and infant's MDI at 18-30 months. Newborn's birth head circumference and infant's MDI at 18-30 months showed an inverted U-shaped association with maternal serum TSH-Z score.