Relationship of Trimester-Specific Maternal Thyroid Function With Gestational Weight Gain And Birth Weight In Pregnant Women With Normal Thyroid Autoimmunity

Abstract Background: Gestational weight gain (GWG) and birth weight are important indicators of maternal and infant health outcomes. Thyroid function may affect body composition and fetal growth during pregnancy. So far, on the premise of excluding thyroid autoimmunity interference, the correlation of thyroid function in different pregnancy with neonatal birth weight and maternal weight gain is still controversial. Methods: This study used data from a prospective birth cohort in Shanghai, China. Serum concentration of TSH, total thyroxine (TT4), free thyroxine (FT4), total triiodothyronine (TT3), free triiodothyronine (FT3), thyroglobulin antibody (TGAb), thyroid peroxidase antibody (TPOAb) were determined using chemiluminescence assay. Maternal GWG and neonatal sex-specific birth weight-for-gestational age Z-score was calculated.Results: Subjects with a higher BMI before pregnancy turned to have a lower GWG and an infant with a higher birth weight. GWG was negatively associated with maternal FT4 at the first and third trimester (p<0.05), and TT4 at the third trimester (p<0.05). GWG was positively associated with maternal FT3 at the second trimester (p<0.05). Lower birth weight Z-score were associated with higher FT4 at the second and third trimester (p<0.05), and higher TT4 at the second trimester (p<0.05). Conclusions: In the general pregnant population with normal thyroid autoimmunity, higher maternal FT4 and TT4 and lower FT3 are associated with less GWG. Higher maternal FT4 and TT4 have an infant with lower birth weight.