A study of the relationship between maternal thyroid status in the first trimester of pregnancy and neonatal outcome

Professor Mark Kilby, Department of Fetal Medicine, Birmingham Women's Hospital

Final report

This project is now complete and has been accepted as an abstract in both the Society of Gynecological Investigation in Houston, Texas (March 2004), the British Endocrine Society (March 2004) and the American Endocrine Society (June 2004).

In a cohort of 280 women with clinically uncomplicated pregnancies who were recruited between April 1996 and July 1997, blood was taken at 14 weeks gestation. Using a cut-off of the lower limit of normal for free thyroxine and TSH concentrations, only 1.3% of the total cohort (who were completely asymptomatic) and pregnant had maternal hypothyroixaemia.

Of those women that had normal thyroid hormone concentrations, it was noted that body mass index was negatively related to maternal thyroxine concentration and positively correlated with TSH.

Interestingly, at birth, the maternal free thyroxine concentration measured at 14 weeks was related to birth length, as well as head circumference.

Therefore, in this cohort of clinically uncomplicated pregnancies in the UK, maternal thyroxine in early pregnancy appears to be associated with differences in fetal size at birth, as well as maternal size.