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Thyroid Function in Early Pregnancy in Japanese Healthy Women: Relation to Urinary Iodine Excretion, Emesis, and Fetal and Child Development

Palmore Hospital (Y.O., H.O., K.S., M.H., K.M., Y.T., S.S., M.U., K.K., T.N., N.T., M.M.), Kobe 470, Japan; Kuma Hospital (S.K., N.A., A.M.), Kobe 650-0011, Japan; and Department of Laboratory Science (K.I.), Yamaguchi University Graduate School of Medical Sciences, Ube, Yamaguchi 755-8505, Japan

Address all correspondence and requests for reprints to: Sumihisa Kubota, Kuma Hospital, 8-2-35 Shimoyamate-Dori, Chuo-Ku, Kobe 650-0011, Japan. E-mail: kubota{at}kuma-h.or.jp.

Context: The effect of constant rich iodine intake, especially during pregnancy, has not been well understood.

Objective: The objective was to examine urinary iodine excretion and thyroid function in early pregnancy in Japanese healthy women. We also studied fetal maturation and child development in these women.

Design and Setting: This study was an observational, prospective study conducted at a maternity hospital.

Subjects: Subjects were 622 pregnant women who visited a maternity hospital consecutively in early gestation. Subjects with positive thyroid antibodies were excluded, and finally 514 subjects were examined. Offspring subjects were infants born to the maternal subjects.

Main Outcome Measures: Thyroid function, serum thyroperoxidase antibodies, and urinary concentrations of iodine were measured at the initial obstetrical visit. The fetal maturation scores estimated by the Dubowitz and Ballard methods in newly born infants were assessed. A child developmental test was performed using the Enjoji Scale up to 12 months of age.

Results: The distribution of urinary iodine concentrations was large, and the average was extremely high. There were significant positive correlations between urinary iodine and serum TSH (r = 0.1326; P < 0.005). Serum TSH during early pregnancy in mothers had no relevance to parameters in neonates, scores of fetal maturation, or child developmental testing in their infants.

Conclusions: Iodine excess during early pregnancy seems to have no adverse effects on the fetus in healthy Japanese women. To avoid hypothyroidism, reducing excess dietary iodine intake to moderate intake may be beneficial for pregnant woman in Japan.