Effect of Reproductive Status and Body Mass Index on Serum Concentrations of Thyroid Hormones and Thyroid-stimulating Hormone in Women in Zaria, Northern Nigeria

Background: Optimum thyroid hormones level is important for the well-being of the fetus and mother. Thyroid hormones disorders have negative impact on female reproduction resulting in reduced fertility and pregnancy morbidities. There is paucity of data on normal levels of circulating thyroid hormones in women of reproductive age in Zaria, Nigeria. The aim of the study was to determine reference values of serum thyroid hormones and thyroid stimulating hormones and the influence of reproductive status and body mass index (BMI) on the reference values of thyroid hormones and thyroid-stimulating hormone in women of reproductive age in Zaria. Methodology: This is a cross-sectional study conducted on 176 women, comprising 65 pregnant, 51 lactating and 60 non-lactating women living within Zaria metropolis. A single blood sample was collected from each of the subjects for the purpose of this study (total blood samples = 176). Blood serum was used to assay for thyroxine (T4), free triiodothyronine (fT3) and thyroid stimulating hormones (TSH) using an ELISA kit. Results: Lactating women had significantly lower (P < 0.01) serum fT3, T4 and TSH than non-lactating and pregnant women. Serum fT3 and T4 were higher in second trimester than in first and third trimesters (P < 0.05). Pregnant women had significantly lower (P < 0.01) BMI compared to lactating and non-lactating women. There was a negative correlation between BMI and fT3 which was only significant (P < 0.01) in pregnant women. A significant (P < 0.01) positive correlation between BMI and TSH was obtained in pregnant women, and a negative correlation (P < 0.05) in non-pregnant women was observed. Conclusion: The present study, provided preliminary reference values of thyroid hormones (fT3, T4) and TSH; and demonstrated that reproductive status and BMI significantly affect these values in women in Zaria, Nigeria