Thyroid Research Thyroid Research Archive Pregnancy

Neurodevelopment may be delayed in infants of mothers with low serum free thyroxine values in early pregnancy

(November 2003)

The background of the study. The neurodevelopment of infants of mothers with overt hypothyroidism is impaired. This study assessed the neurodevelopment of infants whose mothers had low serum free thyroxine (T4) concentrations, but not hypothyroidism, during early pregnancy.

How the study was done. The study began with enrollment of healthy women at 12 weeks' gestation who had a serum free T4 concentration in the lowest 10th percentile or the 50th to 90th percentile. The study subjects were 63 one-year-old and 57 two-year-old infants in the low serum free T4 group and 62 one-year-old and 58 two-year-old infants in the higher serum free T4 group. Infant development was assessed using the Bayley Scales of Infant Development, which includes a Mental Scale (coordination, language development) and a Psychomotor Scale (motor development).

The results of the study. At age one year, 19 infants had delayed mental function (defined as a score <84), 15 of whom (79 percent) were in the low serum free T4 group; the respective numbers at two years of age were 11 and 8 (73 percent). At one year of age, 21 infants had delayed motor function, 16 (76 percent) of these were in the low serum free T4 group; the respective numbers at two years of age were 22 and 17 (77 percent).

The conclusions of the study. Neurodevelopmental delay can occur in infants whose mothers have low serum free T4 concentrations early in gestation.

The original article. Pop VJ, Brouwers EP, Vader HL, Vulsma T, van Baar AL, de Vijlder JJ. Maternal hypothyroxinaemia during early pregnancy and subsequent child development: a 3-year follow-up study. Clin Endocrinol 2003;59:282-8.