Subclinical Hypothyroidism is a condition where the thyroid gland's function begins to decline, but without noticeable symptoms. This is detected through blood tests, where the thyroid hormones (T3 and T4) remain normal, but the thyroid-stimulating hormone (TSH) from the pituitary gland is higher than normal. People with this condition do not show symptoms, and the thyroid hormone levels (Free T3 and Free T4) are normal, but the TSH level is elevated. The normal reference range for TSH is generally below 2.5 mIU/L. However, during pregnancy, normal TSH levels vary depending on the trimester: in the first trimester, it should be below 2.5 mIU/L; in the second trimester, below 3 mIU/L; and in the third trimester, below 3.5 mIU/L.

There is no clear evidence linking subclinical hypothyroidism with infertility, but in patients with this condition, it is important to monitor during pregnancy. This is because there is a possibility that the condition may change and become more severe over time.

Pregnancy in women with thyroid problems: In cases of hypothyroidism (low thyroid function), treatment typically involves thyroid hormone replacement. Those with low thyroid function from the start may experience issues with ovulation, leading to infertility. Both low and high thyroid levels can result in infertility. It is important to assess the current treatment stage if thyroid levels are high, and whether the condition is under control. With consistent treatment and regular medication, thyroid levels can stabilize, allowing for normal ovulation and increasing the chances of pregnancy. Once pregnancy is achieved, it is essential to receive care and monitoring from an obstetrician and endocrinologist specializing in thyroid disorders to maintain normal thyroid hormone levels. This will help prevent complications such as miscarriage, low birth weight, preeclampsia, preterm labor, and the risk of the baby having thyroid issues (either low or high thyroid).