Low maternal iodine intake and early pregnancy hypothyroxinemia: Possible repercussions for children

OBJECTIVE: Recent studies have shown that early pregnancy hypothyroxinemia (lower free thyroxin [FT(4)] and normal thyroid stimulating hormone [TSH] concentration) has deleterious effects on neuro-intellectual development of children. This study was designed to know its incidence in local pregnant women. MATERIALS AND METHODS: Urinary iodine (UI) and serum thyroid related hormone (FT(4), free triiodothyronine [FT(3)], and TSH) were determined in 254 pregnant women during the first trimester. UI and thyroid related hormones were determined by colorimetric (Sandell-Kolthoff) and radioimmunoassay method respectively. RESULTS: Most of the pregnant women (n = 202; 79.5%) were iodine deficient (ID; UI <100 μg/L) and only 52 (20.5%) women were taking sufficient iodine (IS; UI ≥ 100 μg/L). Mean levels of FT(4), FT(3), and TSH were 13.0 ± 2.8 pmol/L, 3.8 ± 1.1 pmol/L and 1.2 ± 1.1 mIU/L, respectively. Maternal FT(4) levels were significantly correlated with UI (r = 0.36; P < 0.001). Mean FT(4) level in IS women was significantly (P < 0.05) higher than ID women. However, mean FT(3) and TSH levels were not significantly different in both groups. FT(4) reference range in IS pregnant women was 10.2-19.4 pmol/L. Hypothyroxinemia (FT(4) <10.2 pmol/L and TSH <2.5 mIU/L) was diagnosed in 30 (11.8%) pregnant women. Its incidence was almost entirely confined to ID pregnant women with an odd ratio of 8.5 (95% confidence interval: 1.1-64.3). CONCLUSION: About 12% pregnant women residing in urban areas of Pakistan are hypothyroxinemic because of low iodine intake.