Effects of iodine nutrition during pregnancy and lactation on postpartum thyroid function in women with subclinical hypothyroidism / 中华内分泌代谢杂志

ABSTRACT

Objective To evaluate the effects of maternal iodine nutrition levels on postpartum thyroid function, and to provide clinical evidence for accurate iodine supplementation in women with subclinical hypothyroidism during pregnancy. Methods This study collected single-pregnant women who had no history of thyroid diseases before pregnancy in our city. Thyroid function and urinary iodine results were continuously recorded during pregnancy and lactation. All subjects were divided into subclinical hypothyroidism group and euthyroidism group according to their thyroid function during pregnancy. The relationship between urinary iodine levels during pregnancy and lactation with postpartum thyroid function were analyzed. Results A total of 148 maternal women were collected, including 41 cases of subclinical hypothyroidism group and 107 cases of euthyroidism group. The urinary iodine level in pregnant women was higher than that in lactation ( median 174.75 vs 149.89μg/L, P<0.05) . However, the iodine deficiency ratio(23.6％) during pregnancy was higher than that during lactation (5.4％). There were significant differences in the change of urinary iodine in each time interval during pregnancy and lactation ( P<0.05). A total of 56 maternal women developed postpartum thyroiditis ( PPT). The incidence of PPT in pregnant women with TPOAb-positive in early pregnancy was higher than that in TPOAb-negative patients (χ2=10.811, P=0.001) . The urinary iodine concentration in the 12-month postpartum period was lower in women with PPT than that in womenwithoutPPT(P<0.05).Coxregressionanalysisshowedthatiodinedeficiencyduringlactation(HR=3.870, 95％CI 1.595-9.392, P=0.003) and TPOAb positive in early pregnancy (HR=3.679, 95％ CI 1.466-9.233, P<0.05) increased the risk of PPT. Subgroup analysis also showed a similar risk increase of PPT in women with hypothyroidism during pregnancy (HR=8.318, 95％CI 2.383-29.029, P<0.05). However, this association was not found in euthyroidism group. Conclusion The urinary iodine level of women during pregnancy and lactation in our iodine suitable areas is within normal range, but attention should still be paid to the effect of iodine deficiency on breast-feeding women, especially among those with subclinical hypothyroidism.