Thyroid Autoantibodies Troublesome in Pregnancy

October 25, 2016
Jeannette Y. Wick, RPh, MBA, FASCP

Overt clinical hypothyroidism increases placental abruption, gestational diabetes, premature membrane rupture, preterm birth, low birth weight, and perinatal mortality risk.

Normal maternal thyroid function is crucial to proper fetal neurological development during the first trimester and reproductive success throughout the pregnancy. Thyroid autoimmunity is the most common cause of thyroid dysfunction in women of reproductive age. Up to 25% of women of reproductive age have auto-thyroid antibodies, but most do not have overt clinical signs of thyroid dysfunction. Different professional societies disagree about thyroid dysfunction screening and treatment.

An ahead-of-print article in Seminars in Reproductive Medicine proposes thyroid hormone replacement improves reproductive outcomes in expectant mothers with thyroid autoimmunity.

Human chorionic gonadotropin spurs thyroid hormone production yet indirectly suppresses active hormone formation in the plasma. Women with existing hypothyroidism are unable to produce sufficient hormones to maintain adequate levels.

Patients with endometriosis and polycystic ovarian syndrome are at greater risk for thyroid autoimmunity. However controlled ovarian hyperstimulation to combat infertility exacerbates hypothyroidism. In fact, 53% of IVF pregnancies in women with thyroid autoimmunity end in miscarriage compared to 23% in women without auto-thyroid antibodies.

Meta-analysis indicates the presence of autoantibodies triple miscarriage risk in euthyroid patients. Thyroid hormone supplementation reduces miscarriage risk in both hypothyroid and euthyroid women who have autoantibodies. No current evidence supports prophylactic hormone supplementation in women planning to be pregnant.

Overt clinical hypothyroidism increases placental abruption, gestational diabetes, premature membrane rupture, preterm birth, low birth weight, and perinatal mortality risk. Women with autoantibodies are 70% more likely to give birth before 37 weeks and 150% more likely before 34 weeks. Preterm birth and neurologic birth defect risk is especially great in patients with symptomatic hypothyroidism.

The Endocrine Society, American Thyroid Association, American Congress of Obstetrics and Gynecology, and American Association of Clinical Endocrinologists recommend thyroid disorder screening before or during pregnancy. American Congress of Obstetrics and Gynecology and American Association of Clinical Endocrinologists recommend pre-conception and early pregnancy screening in high-risk individuals only.

Auto-thyroid antibodies increase the risk of poor reproductive outcomes even if a mother is euthyroid. Thyroid hormone supplementation is critical to reverse these deleterious effects. Providers should determine screening and follow-up needs on a patient-level basis.

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