No abstract

Thyroid diseases in pregnant and lactating women may result in adverse outcomes for both mothers and infants. A reference range for thyroid function is required in different areas; however, few studies on the gestational change or reference ranges of thyrotropin (TSH) and free thyroxine (FT4) concentrations for Japanese pregnant women have been reported. To establish the gestational trimester-specific reference ranges of serum TSH and FT4 concentrations, our previously published data on 481 pregnant women with the mean age of 30.8 years who provided serum samples as early as gestational week (GW) 6 was compiled by using their percentile values. The overall median urinary iodine concentration (UIC) during pregnancy was 201 μg/L suggesting adequate iodine intake. The prevalence of positive serum thyroid autoantibody (ThAb), i.e., antithyroid peroxidase antibody (TPOAb) and antithyroglobulin antibody (TgAb), was 11.4%. The reference ranges (2.5-97.5th percentile) of serum TSH and FT4 concentration calculated for samples with negative TgAb and TPOAb were 0.04-6.06 mIU/L in the first trimester (T1), 0.31-3.11 mIU/L in the second trimester (T2) and 0.48-3.93 mIU/L in the third trimester (T3) for TSH, and 1.10-1.87 ng/dL (T1), 0.76-1.56 ng/dL (T2) and 0.76-1.14 ng/dL (T3) for FT4. Compared to published data around the world in the 2017 American Thyroid Association (ATA) guideline, both the upper and lower limits of our TSH and FT4 reference ranges in the first trimester were higher than those in other countries. Further research is necessary in larger samples.

An adequate maternal iodine intake during pregnancy and lactation is essential for growth and mental development in fetuses and newborns. Both deficient and excess iodine may disrupt normal thyroid function. There are limited data on perinatal iodine metabolism in mothers and infants, as well as the effect of povidone-iodine (PVP–I) antiseptics used in Cesarean delivery. The urinary iodine concentration (UIC), serum iodine, thyrotropin (TSH), free thyroxine (FT4) and breast milk iodine concentration (BMIC) were measured consecutively in a total of 327 mothers and 249 term-infants in two prospective studies. The maternal median UIC was 164 µg/L in the third trimester, increased to 256 µg/L on postpartum day 2, then decreased to 116 µg/L one month later. The BMIC on postpartum days 2 and 30 was 17.6 and 13.5 µg/100g, respectively. In neonatal infants born to the mothers unexposed to PVP-I, the median UIC was 131 µg/L in the first voiding urine and increased to 272 µg/L on day 4, then slightly decreased to 265 µg/L on day 28 suggesting sufficient iodine reserve at birth. PVP-I antiseptics containing 1g of iodine for skin preparation at Cesarean delivery transiently increase maternal serum iodine concentration, UIC and BMIC, however, it has little effect on maternal TSH, FT4 and neonatal UIC, TSH, or FT4. The iodine status of pregnant women and their infants was adequate in this population; however, the UIC in lactating mothers at one postnatal month was low enough to suggest iodine deficiency or near iodine deficiency. Further studies are necessary. This study was not registered to any clinical trials registry (CTR).

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