Diagnosis and management of clinical hypothyroidism in pregnancy The diagnostic criteria for clinical hypothyroidism in pregnancy are: serum TSH > upper gestational reference value and serum FT4 < lower gestational reference value. (See Maternal Thyroid Disease Guidelines Summary) What are the risks of hypothyroidism in pregnancy on pregnancy outcome? The prevalence of hypothyroidism in pregnancy is reported to be 1% in China. Hypothyroidism in pregnancy is associated with a 60% increased risk of miscarriage, a 22% increased risk of gestational hypertension, and an increased risk of stillbirth. The most common cause of clinical hypothyroidism is autoimmune thyroiditis (Hashimoto's thyroiditis), which accounts for about 80% of cases. Other causes include thyroid surgery and iodine 131 treatment. Fetal death in pregnant women with untreated clinical hypothyroidism. Miscarriage. The incidence of circulatory malformations and low birth weight is significantly increased. With effective treatment, there is no evidence of adverse pregnancy outcomes and harm to fetal mental development.