The thyroid gland is a butterfly-shaped organ located in the lower part of your neck. It sits a little below the Adam's apple (the laryngeal prominence) and above the collarbone (clavicle). This gland is part of the endocrine system and plays an essential role in women's health. It is an important gland for normal growth, metabolism, energy production, reproduction, temperature control, digestion, and brain development. Hypothyroidism occurs when the thyroid in underactive and doesn’t produce enough hormones.
Hormonal birth control contains the hormones estrogen, progesterone, or a combination of both in various forms. The reproductive hormones including estrogen work closely with thyroid hormones. The estrogen in most hormonal birth control can alter how thyroid hormones are made, used, and converted. Studies have suggested that longtime use of hormonal birth control is strongly associated with hypothyroidism. This is especially true for those who have taken hormonal birth control for over 10 years. Therefore, when treating hypothyroidism, drugs, including hormonal birth control, can affect how thyroid medication is absorbed and can decrease its effectiveness. Examples of drugs that can affect thyroid meds are hormonal birth control, estrogen replacement, testosterone replacement, seizure meds, certain antidepressants, sedatives for anxiety, cholesterol meds, and drugs to treat tuberculosis. The administration of such drugs which includes antacids, calcium, iron, multivitamins, and cholesterol meds should be at least 4 hours from ingestion of the thyroid medication.
In conclusion hypothyroidism may cause infertility, by preventing ovulation, the release of an egg from the ovary. However, correcting thyroid hormone levels with medications often resolves this issue. In one study, 76.6% of women with infertility due to hypothyroidism got pregnant within six weeks to a year after starting thyroid medication. Another smaller study showed that 33% of women got pregnant six weeks to two years after starting thyroid medication.
Ref:
https://www.verywellhealth.com/the-effects-of-pregnancy-on-the-thyroid-and-tsh-levels-3232932#citation-1 
