Thyroid and Pregnancy With hypothyroidism, your thyroid gland doesn't produce enough of certain important hormones. Low levels of thyroid hormone can interfere with the release of an egg from your ovary (ovulation), which impairs fertility. It is important that TSH is at an optimal level, as it affects ovulation; up to 5% of women struggling to conceive have abnormal thyroid hormone levels. However, recent studies have suggested that TSH should be no higher than 2.5 when trying to conceive and 3.0 during pregnancy.