Antenatal hypothyroidism does not lower IQ

The randomised trial measured thyrotropin and free thyroxin (T4) in more than 21,800 Italian and British women at around 12 weeks’ gestation.

A screening group had results and treatment immediately, while controls had serum stored and measured after birth. Some 390 screened women and 404 in the control group tested positive for thyrotropin levels above 97.5th percentile, free T4 levels below the 2.5th percentile, or both. 

Women in the screening group received 150μg of levothyroxine daily adjusted to achieve targets. 

An IQ test among offspring at the age of three years showed no significant difference in IQ between offspring of the two groups.

Among children from the screened group, 12.1% had an IQ of less than 85 compared to 14.1% from controls. 

Professor Michael Permezel, vice-president of RANZCOG, said the research was relatively reassuring and backed current advice to screen only pregnant women at