The effect of maternal thyroid function in the first half of pregnancy on the neurologic development of 20 infants in the first two years of life was studied at the University of Amsterdam and Emma Children’s Hospital, The Netherlands. At the age of 6 and 12 months, the mean mental developmental index (MDI) score was 16 points lower for 7 infants born to mothers with subclinical hypothyroidism compared to 6 with euthyroid mothers (P= .03 and .02, respectively). At 24 months, a mean 6 point lower MDI score was not statistically significant. One infant out of 7 born to mothers with hyperthyroidism developed transient hyperthyroidism, but none showed changes in the MDI. Motor nerve conduction, somatosensory evoked potentials, and Bayley scales showed no differences among groups. 
COMMENT. Maternal subclinical hypothyroidism in the first half of pregnancy is associated with a lower mental development score in the infants during the first year of life. Optimal treatment of maternal thyroid disease throughout pregnancy is emphasized.
Low triiodothyronine levels in preterm infants are correlated with a 6.6 point deficit in Full Scale IQ scores on the WISC Scales at 8 year follow-up, and an increased risk of developing cerebral palsy and cognitive deficits is reported in premature infants with low thyroxine levels in the first week of life. Some authorities caution that thyroxine therapy for hypothyroid mothers is unlikely to benefit premature babies, and triiodothyronine replacement in premature infants may be dangerous. Neonatologists generally withhold therapy pending a retest after the infant reaches term. (See Progress in Pediatric Neurology III, 1997;pp 281-2).