A Longitudinal Study of Changes in Thyroid Related Hormones among Pregnant Women Residing in an Iodine Deficient Urban Area

Problem Statement. Thyroid gland in women undergoes functional changes during pregnancy. A few studies have described such changes in pregnant women residing in iodine deficient areas. Objective. To document these changes in pregnant women residing in Lahore, a low iodine intake urban area of Pakistan. Patients and Methods. In 254 pregnant women, data of FT(4), FT(3), and TSH during the first and subsequent trimesters were obtained and compared with those of 110 nonpregnant women. These hormones were determined in serum by radioimmunoassay (RIA) techniques using commercial kits. Results. Compared to nonpregnant women mean FT(4) level was decreased, and FT(3) and TSH increased significantly (P < 0.05) in pregnant women. A negative correlation of FT(4) with TSH was observed in all three trimesters. Serum FT(3) was positively correlated with TSH only during the third trimester. As a function of gestation time, FT(4) levels progressively decreased, and FT(3) and TSH levels increased significantly (one-way ANOVA F = 108.2, 17.3, and 44.8, resp.; all P < 0.05) exhibiting thyroid gland adaptations. Conclusion. Pregnancy is associated with significant alterations in thyroid function due to low iodine intake in women residing in study area. The compensated thyroid function poses a risk of thyroid failure in a number of pregnant women.