Estimate the proper thyroid screening method during pregnancy. Evaluate if maternal subclinical hypothyroidism treatment during pregnancy result in improved pregnancy outcome and cognitive function in the children.

The investigators conducted a single-blinded trial in which pregnant women at a gestation of less than 12 weeks, usually 6 to 8 weeks, provided blood samples for measurement of thyrotropin, free thyroxine(FT4) and thyroid peroxidase antibody (TPOAb). Women were assigned to a screening group in PUMCH (in which measurements were obtained immediately) or a control group in HMCHH (in which serum was stored and measurements were obtained shortly after delivery). Each group enrolled 1000 pregnant women separately. Women with positive findings in the screening group were given individualized levothyroxine treatment and regular follow-up. Compare the pregnancy outcomes, IQ at 2-3 years of age in children of women with subclinical hypothyroidism between two groups.

Inclusion Criteria:

• All of the pregnant women who receive prenatal care in PUMCH and HMCHH
• Sign the consent form
• agree to follow-up the pregnancy outcome and child

Exclusion Criteria:

• the pregnant women who do not agree to enter the study