Endocrine Abstracts

Thyroid hormone (TH) is essential for fetal development and before 14 weeks maternal supply of TH is critical to the fetus. Subtle abnormalities of maternal thyroid status have been reported to affect neurodevelopment in childhood (1,2). To explore this further, we examined the relationship between maternal thyroid status and newborn measures of growth potential. A cohort of uncomplicated pregnant women (n=480) was recruited. At antenatal booking (mean gestation 13.05 weeks) maternal FT4 and TSH were determined. At birth, neonatal anthromorphological measurements (birthweight, head circumference, birth length, and triceps skin fold thickness) were made. All data were log. transformed and represented as mean (SEM and range). Mean booking FT4 was 13.1 pmol/L (8.2-21.8) and TSH 2.02 mU/L (0.1-20.8). Maternal FT4 was inversely related to TSH (r=-0.03; P<0.001). Both FT4 and TSH were correlated with maternal booking body mass index (BMI), FT4 negatively related (r= -0.16; p = 0.01) and TSH positively (r = 0.20; p <0.001). There was no relationship between maternal FT4 or TSH and fetal ultrasound biometry at 20 or 30 weeks gestation although there was a trend with time. At birth, maternal booking FT4 (but not TSH) was related to fetal birth length (r =-0.16; p = 0.01), as well as head circumference (r = -0.13; p <0.007), even after adjustment for parity, smoking and obstetric complications. Using FT4 < 9 pmol/L and TSH >6 mU/L, 1.3% of the cohort had maternal hypothyroidism. There was no significant difference in the prevalence of preterm delivery, APH or pre-eclampsia in subgroups of euthyroid and hypothyroid women. Maternal FT4 in early pregnancy was thus associated with differences in fetal measurements at birth, highlighting the influence of maternal thyroid status on early human development. 1. Pop V et al. Clin Endocrinol 1999;50(2):149-55. 2. Haddow J et al. NEJM 1999;341:549-55.