Maternal thyroid dysfunction during pregnancy are associated with adverse pregnancy outcomes.Interpretation of thyroid function tests during pregnancy can be difficult because of complex hormonal changes.Non-pregnant diagnostic criteria of thyroid function can lead to gestational hypothyroidism and hyperthyroidism misdiagnosed and inadequate doses of medication.Therefore,to establish gestation-specific reference intervals for thyroid function tests is very important to improve management of thyroid disease in pregnancy.To maintain maternal euthyroidism can decrease adverse obstetrical and neonatal outcomes and has very important significance to the national policy of China's prenatal and postnatal cares.