Abstract: Objective: To investigate the relationship between subclinical hypothyroidism (SCH) during pregnancy and maternity anemia in late gestation, and to analyze if the treatment with oral levothyroxine (LT4) can improve the incidence of anemia. Methods：1 087 gravidas with SCH (the SCH group) and 4 942 gravidas with normal thyroid function (the control group) diagnosed by the serum thyroid function screening during prenatal care were included in this retrospective case-control study. All gravidas with the anemia during early pregnancy were excluded. The SCH group were then divided into the SCH-treated subgroup and the SCH-untreated subgroup according to whether they were treated with LT4. The positive rate of TPOAb and the incidence of anemia were compared among groups. Results：①The positive rate of TPOAb in the SCH group was significantly higher than that in the control group (23.4% vs. 9.4%, χ2=163.920, P=0.000). ②The incidence of anemia in the SCH group was significantly higher than that in the control group (25.4% vs. 21.0%, χ2=9.459, P=0.002), while this incidence in the SCH-treated subgroup was lower than that in the SCH-untreated subgroup (22.9% vs. 26.5%, but P=0.204). Conclusions：SCH increases the incidence of anemia during last trimester in gestation period. LT4 treatment may improve the incidence of SCH-maternity anemia in late gestation.

Key words: Thyroxine, Hypothyroidism, Anemia, Incidence, Pregnant women