Clinical hypothyroidism in pregnancy may impair the neurointellectual development of the offspring and increase the risk of preterm delivery, miscarriage, low birth weight babies, stillbirth and gestational hypertension. Diagnostic criteria for clinical hypothyroidism in pregnancy:TSH is above the upper limit of the reference value for pregnancy Free T4 is below the lower limit of the reference value. If the serum is greater than 10mIU/L, regardless of whether the free T4 is reduced, it is treated as clinical hypothyroidism.