Clinical trial registration number: NCT00791466.
Overweight increases risk of first trimester hypothyroxinaemia in iodine-deficient pregnant women
Article first published online: 13 AUG 2013
© 2013 John Wiley & Sons Ltd
Maternal & Child Nutrition
Volume 10, Issue 1, pages 61–71, January 2014
How to Cite
Gowachirapant, S., Melse-Boonstra, A., Winichagoon, P. and Zimmermann, M. B. (2014), Overweight increases risk of first trimester hypothyroxinaemia in iodine-deficient pregnant women. Maternal & Child Nutrition, 10: 61–71. doi: 10.1111/mcn.12040
- Issue published online: 17 DEC 2013
- Article first published online: 13 AUG 2013
- Swiss National Science Foundation (Bern, Switzerland)
- Swiss Federal Institute of Technology (ETH) Zurich (Switzerland)
- iodine deficiency;
- pregnant women;
- thyroid dysfunction;
Hypothyroxinaemia early in pregnancy may impair fetal brain development. Increased body weight has been associated with low thyroxine concentrations in non-pregnant women. In pregnant women, morbid maternal obesity is a risk factor for thyroid dysfunction. But whether lesser degrees of overweight that are much more common could be a risk factor for hypothyroxinaemia in pregnancy is unclear. The objective of this study was to investigate if overweight increases risk for thyroid dysfunction, and specifically hypothyroxinaemia, in iodine-deficient pregnant women. We performed a cross-sectional study at first hospital visit among healthy Thai pregnant women. We measured weight and height, urinary iodine concentration (UIC), serum thyroid hormones and thyroglobulin. Pre-pregnancy weight and relevant dietary factors were determined by questionnaire, and body mass index (BMI) was used to classify weight status. Among 514 women (mean gestational age, 11 weeks) with a median UIC of 111 μg dL–1, indicating mild iodine deficiency, 12% had low free thyroxine (fT4) concentrations: 3% had overt hypothyroidism; 7% had subclinical hypothyroidism; and 8% had isolated hypothyroxinaemia. Based on pre-pregnancy BMI, 26% of women were overweight or obese. In a multiple regression model, BMI was a negative predictor of fT4 (β = −0.20, P < 0.001). Compared to normal weight women, the prevalence ratio (95% CI) of a low fT4 in overweight women was 3.64 (2.08–6.37) (P < 0.01). Iodine-deficient pregnant Thai women who are overweight have a 3.6-fold higher risk of hypothyroxinaemia in the first trimester compared to normal weight women. Targeted screening should consider overweight a potential risk factor for thyroid dysfunction in pregnant women in iodine-deficient areas.