The association between serum TSH concentration whithin the normal range and nutritional status in euthyroid pregnant women at the first trimester of gestation

Background: Follow-up studies have shown an increased risk of thyroid dysfunction in individuals with normal serum thyroid-stimulating hormone (TSH) levels. Furthermore, the possible consequences of minor differences in thyroid function (without achieving poor thyroid function) in the risk of weight gain during pregnancy are questionable, too. The production of TSH is under the hypothalamus-pituitary control, and food is one of the most effective environmental agents that control hypothalamic-pituitary-thyroid axis activity. Regarding the few available studies, we assessed the association of minor variations of TSH concentrations and nutritional status in the first trimester of pregnancy. Materials and Methods: This cross-sectional descriptive and analytical study was performed on 150 primiparous healthy women. Demographic and family characteristics were collected using a researcher-administered questionnaire. Nutrients intake were extracted from a 72-h recall, and physical activity scores were determined by the pregnancy physical activity scale. Results: The prepregnancy body mass index (BMI) (beta =0.022, P = 0.004) and participants' weight at 6-10 weeks of gestation (beta =0.006, P = 0.024) were positively associated with TSH concentrations, while total physical activity score was negatively correlated (beta = -0.006, P = 0.047). We did not find any significant association between TSH values and energy-adjusted nutrients intake (P > 0.05). Conclusion: We suggest that differences in TSH concentrations within normal range in the first trimester are correlated with gaining weight, physical activity level, and prepregnancy BMI. TSH concentration and consequently thyroid function may influence on gestational weight gain or vice versa.