Hypothyroidism / Subclinical Hypothyroidism

Hypothyroidism is a condition in which the thyroid gland does not make enough thyroid hormone. In regions where diets contain enough iodine, the most common cause is Hashimoto's thyroiditis, an immune attack on the thyroid. A blood test confirms the full form, overt hypothyroidism. In this form, TSH, the brain's signal to the thyroid, is high. Free T4, the main thyroid hormone, is low. In the milder form, subclinical hypothyroidism, TSH is high but free T4 stays normal. Both forms can affect fertility. The milder form is linked to ovulation problems, impaired implantation, and a higher risk of miscarriage. These effects can occur even when a woman feels well.¹

Thyroid antibodies add risk on their own, apart from TSH. One meta-analysis studied women with normal thyroid levels. Women with thyroid peroxidase antibodies (TPO-Ab) had higher rates of miscarriage and preterm birth than women without them.² A normal TSH alone does not rule out a thyroid problem. A full thyroid evaluation adds antibody testing to the TSH test.

Restorative care looks for the cause before it treats. RRM clinicians may check thyroid levels and antibodies when a couple faces infertility or recurrent pregnancy loss. The milder form and thyroid antibodies both track with ovulation problems, implantation problems, and pregnancy loss. This pattern holds even when TSH sits inside the standard range. A Cochrane review studied thyroxine, a thyroid hormone medicine, for women with difficulty conceiving who had the milder form or thyroid antibodies. It rated the trial evidence as low certainty and too limited to settle treatment questions.³ Those trials tested one medicine in women selected by a lab marker. The pattern in the wider studies still stands. Treatment rests on each woman's labs and history, not on one blanket plan.

Low thyroid function can also affect the luteal phase, the second half of the cycle. The body needs thyroid hormone to make normal amounts of progesterone. The corpus luteum, the structure that makes progesterone after ovulation, also depends on it. Women with luteal phase deficiency or repeated early pregnancy loss have good reason for a thyroid evaluation before any hormone support begins. When treatment is needed, correcting the thyroid first addresses the problem at its source.