Which of the following is a common cause of hypothyroidism in pregnancy?

• A. Hashimoto's thyroiditis
• B. Graves' disease
• C. Hyperemesis gravidarum
• D. Preeclampsia

Answer: (A)

Autoimmune destruction of the thyroid, as seen in Hashimoto's thyroiditis, is the most common cause of hypothyroidism in pregnancy. In regions with adequate iodine, autoimmune thyroid disease is a frequent reason maternal thyroid function falls short of needs during pregnancy, since the gland’s ability to produce thyroid hormone is diminished by immune-mediated damage. This can be unmasked or worsened by the increased hormonal demands of pregnancy, making Hashimoto's the typical culprit.

Graves' disease would cause hyperthyroidism, not hypothyroidism, because it involves stimulating antibodies that raise thyroid hormone production. Hyperemesis gravidarum can lead to transient thyrotoxicosis through high hCG stimulating the thyroid, but it does not cause a sustained hypothyroid state. Preeclampsia is a placental disorder affecting blood pressure and organ function, not a thyroid problem.