Maternal thyroid deficiency during pregnancy and subsequent neuropsychological development of the child

Background When thyroid deficiency occurs simultaneously in a pregnant woma n and her fetus, the child's neuropsychological development is adversely af fected. Whether developmental problems occur when only the mother has hypot hyroidism during pregnancy is not known. Methods In 1996 and 1997,we measured thyrotropin in stored serum samples co llected from 25,216 pregnant women between January 1987 and March 1990. We then located 47 women with serum thyrotropin concentrations at or above the 99.7th percentile of the values for all the pregnant women, 15 women with values between the 98th and 99.6th percentiles, inclusive, in combination w ith low thyroxine levels, and 124 matched women with normal values. Their s even-to-nine-year-old children, none of whom had hypothyroidism as newborns , underwent 15 tests relating to intelligence, attention, language, reading ability, school performance, and visual-motor performance. Results The children of the 62 women with high serum thyrotropin concentrat ions performed slightly less well on all 15 tests. Their full-scale IQ scar es on the Wechsler Intelligence Scale for Children, third edition, averaged 4 points lower than those of the children of the 124 matched control women (P=0.06); 15 percent had scores of 85 or less, as compared with 5 percent of the matched control children. Of the 62 women with thyroid deficiency, 4 8 were not treated for the condition during the pregnancy under study. The full-scale IQ scores of their children averaged 7 points lower than those o f the 124 matched control children (P=0.005); 19 percent had scores of 85 o r less. Eleven years after the pregnancy under study, 64 percent of the unt reated women and 4 percent of the matched control women had confirmed hypot hyroidism. Conclusions Undiagnosed hypothyroidism in pregnant women may adversely affe ct their fetuses; therefore, screening for thyroid deficiency during pregna ncy may be warranted. (N Engl J Med 1999;341:549-55.) (C)1999, Massachusett s Medical Society.