What is the role of thyroid function in fertility?

• A. Thyroid disorders only affect conception; not ovulation or implantation.
• B. Hypothyroidism improves fertility by increasing ovulation.
• C. Thyroid disorders (hypo- or hyperthyroidism) can disrupt ovulation and implantation; achieving euthyroid state improves fertility outcomes.
• D. Thyroid function has no impact on fertility.

Answer: (C)

Thyroid status directly influences both the hormones that drive ovulation and the uterine environment needed for implantation. When thyroid function is off, the normal signaling from the brain to the ovaries can be disrupted, leading to irregular or absent ovulation. At the same time, thyroid hormones affect endometrial receptivity—how well the lining of the uterus can support an embryo—so implantation can be impaired.

In hypothyroidism, elevated TRH can raise prolactin levels, which suppresses GnRH and blunts the LH/FSH pulses needed for ovulation. The endometrium may also be less receptive. In hyperthyroidism, menstrual cycles often become irregular or suppressed due to altered gonadotropin release, and autoimmune thyroid disease can increase miscarriage risk. Importantly, restoring normal thyroid function (euthyroid state) improves ovulatory function and endometrial conditions, leading to better fertility outcomes.

So thyroid disorders disrupt both ovulation and implantation, and achieving euthyroidism generally improves the chances of conceiving and carrying to a successful pregnancy.