Neurologic development of the newborn and young child in relation to maternal thyroid function

A prospective observational study was performed in pregnant women with know n thyroid disease. We studied the effect of maternal thyroid function in th e first half of pregnancy on the neurologic development of the infant in th e first 2 y of life. Clinical and thyroid function data were collected from 20 pregnant women with known thyroid disease and their newborn children. I nfants were divided into three groups according to their maternal thyroid f unction within the first half of pregnancy: Group A (n = 7): maternal subcl inical hypothyroidism, Group B (n = 6): maternal euthyroidism, and Group C (n = 7): maternal hyperthyroidism or subclinical hyperthyroidism. Neurophys iologic, i.e. motor nerve conduction velocity and somatosensory evoked pote ntials and neurologic and developmental (Bayley scales) assessments were do ne. One infant, born to a mother with Graves' disease, developed transient hyperthyroidism. At the age of 6 and 12 mo, the mean mental developmental i ndex (MDI) score was 16 points lower for infants in Group A than for those in Group B (p = 0.03 and 0.02, respectively). At the age of 24 mo, the mean MDI score was 6 points lower, which was not statistically significant. Neu rophysiologic and neurologic assessments and the mean Psychomotor Developme ntal scores did not differ among the three groups. In conclusion, maternal subclinical hypothyroidism in the first half of pre gnancy was associated with a lower mean MDI score in their infants during t he first year of life.