Cappoen J P
Service d'Endocrinologie et Métabolismes, CHU, Lille.
Rev Fr Gynecol Obstet. 1989 Dec;84(12):893-7.
In spite of frequent hypertrophy of the gland, the thyroid function remains normal during pregnancy. Of course, the total thyroid hormones level bound to TBG (Thyroxine Binding Globulin) increases regularly as a result of hyperestrogenism, but the level of the free fractions of the thyroid hormones (FT3, FT4) which is normal during the 1st trimester tends to decrease regularly during the 2nd and 3rd trimesters. There is a moderate decrease of the TSH level during pregnancy. The placenta plays a major role in the synthesis and metabolism of the thyroid function hormones. TSH, T3, T4 and thyroglobulin cannot cross the placental barrier while TRH, iodine, and thyrostimulating immunoglobins can. Among medications, thyroid hormones do not cross the placental barrier contrary to synthetic anti-thyroid preparations (SAT), lithium and beta-blockers. Therefore, this should be taken into consideration in the treatment of dysthyroidisms, knowing that the thyroid gland of the fetus becomes functional at 12 weeks: the secretion of fetal T4 and TSH is present as early as the 18-20th week. The thyroid gland of the fetus has no auto-regulation mechanism and the fetus adjust his hormone secretion according to the iodine environment.
尽管孕期甲状腺常常肥大，但甲状腺功能仍保持正常。当然，由于雌激素水平升高，与甲状腺素结合球蛋白（TBG）结合的甲状腺激素总量会有规律地增加，但甲状腺激素游离部分（FT3、FT4）的水平在孕早期正常，在孕中期和孕晚期往往会有规律地下降。孕期促甲状腺激素（TSH）水平会适度降低。胎盘在甲状腺功能激素的合成和代谢中起主要作用。TSH、T3、T4和甲状腺球蛋白不能穿过胎盘屏障，而促甲状腺激素释放激素（TRH）、碘和促甲状腺免疫球蛋白可以。在药物方面，与合成抗甲状腺制剂（SAT）、锂和β受体阻滞剂不同，甲状腺激素不会穿过胎盘屏障。因此，在治疗甲状腺功能异常时应考虑到这一点，因为胎儿的甲状腺在12周时开始发挥功能：胎儿T4和TSH的分泌早在第18 - 20周就已出现。胎儿的甲状腺没有自动调节机制，胎儿会根据碘环境调整其激素分泌。
