Thyroid hormones profile among obese pregnant Sudanese women

Previous studies evaluating thyroid function among obese pregnant women failed to demonstrate a consistent pattern of thyroid hormones profile, probably due to the variations in biological/environmental determinants of thyroid function in different countries.

The aim of the study was to evaluate thyroid hormones profile in Sudanese pregnant women with varying degrees of obesity.

Obstetric/sociodemographic characteristics were gathered from 178 singleton pregnant Sudanese women using questionnaires. Weight and height were measured; body mass index (BMI) was calculated and categorized into four groups: Underweight (BMI <18.5 kg/m²), normal weight (18.5-24.9 kg/m²), overweight (25.0-29.9 kg/m²), and obese (≥30 kg/m²). Free triiodothyronine (FT3), free thyroxin (FT4), and thyroid-stimulating hormone (TSH) were measured.

Of the 178 enrolled women, 9 (5.1%), 52 (29.2%), 73 (41.0%), and 44 (24.7%) were underweight, normal BMI, overweight, and obese, respectively. FT3 level was significantly higher in obese women compared with normal BMI (P=0.004) as well as overweight women (P=0.015). Higher FT3 levels were significantly associated with obesity (odds ratio [OR]=9.5, 95% confidence interval [CI] =3.1-29.0, P<0.001). Lower levels of FT4 were significantly associated with overweight (OR=0.06, 95% CI=0.007-0.58, P=0.015) and obesity (OR=0.048, 95% CI=0.004-0.5, P=0.018). Based on linear regression analysis, BMI was positively associated with FT3 (4.7 pmol/l, P<0.001) and negatively associated with FT4 (-8.26 pmol/l, P=0.001).

BMI correlates with FT3 differently compared to FT4. Pregnant women with higher BMI are likely to have higher levels of FT3, but lower FT4. In contrast, TSH levels were comparable in different BMI groups.

Increased iodothyronine 5´deiodinase (5´D) activity associated with obesity may give an explanation for thyroid profile in those with higher BMI. High 5´ activity increases FT3 at the expense of FT4. Alternatively, high FT3 and low FT4 are expected to feedback differently on TSH, which explains the loss of positive correlation between BMI and TSH.