甲状腺疾病与妊娠

Thyroid diseases and pregnancy

妊娠期甲状腺激素的产生、循环、代谢、调节以及甲状腺免疫均会随妊娠的不同阶段而改变。相关的改变包括：（1）雌激素刺激的血清甲状腺素结合球蛋白水平升高。（2）由于人绒毛膜促性腺激素与促甲状腺激素（TSH）的同源性导致的甲状腺激素产生增加。（3）碘在胎盘的降解加快和在肾脏的排除增加。母体甲状腺这些生理性的变化为妊娠期甲状腺疾病的诊断和治疗带来困惑，因此，需要建立孕期特异的TSH、总T4和游离T4正常参考范围。遗憾的是，目前尚无这样的标准。如非妊娠状态一样，TSH也可以作为诊断妊娠期甲状腺疾病首选的指标，TSH检测不受方法学的限制，下限介于0．2～0．4mlU／L之间，2．5mlU／L可以作为TSH在妊娠早期正常范围保守的上限。TT4结果稳定，可以通过非妊娠状态的正常值乘以系数1．5来推断妊娠期的参考范围。妊娠期甲状腺功能减退的患者应该接受左旋T4（L-T4）替代治疗，并尽快使TSH低于2．5mlU／L，L-T4的剂量在妊娠期要较妊娠前增加30％～50％。对于妊娠期甲状腺功能亢进的患者，丙硫氧嘧啶是首选的治疗药物。甲状腺功能正常的自身免疫性甲状腺炎的孕妇在妊娠期发生甲状腺功能减退、分娩后发生产后甲状腺炎的危险性提高，应该注意监测甲状腺功能。

The production, circulation, metabolism, regulation of thyroid hormone as well as thyroid immunity in pregnancy change with gestational age. The changes in thyroid function during pregnancy are related to： （ 1）estrogen-mediated increase in circulating levels of thyroid-binding globulin, （2） thyroid stimulation by human chorionic gnnadotropin resulting from structural homology with thyroid stimulating hormone （TSH）, and （3） a relative decline of iodide related to increased renal clearance and overall losses to the fetus and placenta. These changes in maternal thyroid physiology can lead to confusion in the diagnosis or evaluation of thyroid abnormalities. Therefore, establishment of trimester-specific reference ranges for TSH, TT4 and FT4 is urgently needed. Unfortunately, currently there are no reliable trimester-specific reference ranges for these parameters. TSH can be used as first-selected marker for diagnosis of thyroid disease in pregnancy like nonpregnant status. The lower limits of TSH are fairly comparable between TSH assays ranging between 0.2 and 0.4 mlU/L. TSH of 2.5 mlU/L is recommended as an appropriate conservative upper limit for first trimester pregnancy. The TT4 reference range is stable and can be calculated by multiplying the nonpregnant reference ranges by 1.5 for pregnancy. Pregnant women with hypothyroidism should receive L- T4 replacement as soon as possible to the target of 2.5 mIU/L of TSH and L-T4 dosage should plan to increase by 30% to 50% higher early in pregnancy than that before pregnancy. Women with hyperthyroidism receiving antithyroid drugs, especially propylthiouracil, are safe in pregnancy. Women with euthyroid autoimmune thyroid disease in pregnancy are at increased risk for thyroid insufficiency during pregnancy and postpartum thyroiditis and should be monitored with TSH and TT4 during pregnancy and after delivery.