PURPOSE OF REVIEW: To summarize the evidence regarding the need to assess thyroid function in women undergoing ovarian stimulation as well as the need to intervene when thyroid function is suboptimal. RECENT FINDINGS: There is now evidence that ovarian stimulation can influence thyroid function not only via hyperestrogenism but also directly, since thyroid-related receptors are present in human granulosa cells and in the endometrium. Prospective and retrospective observational studies, as well as a few clinical trials, have been conducted in an effort to clarify the association between ovarian stimulation and thyroid function with controversial results. SUMMARY: The need of thyroid function screening with thyroid stimulating hormone (TSH) in infertile women attempting pregnancy is recognized by many international societies. Since TSH is a simple, cheap screening tool and levothyroxine (LT4) supplementation is an easy to apply, cheap and well tolerated intervention, universal thyroid screening in women undergoing IVF represents a reasonable policy. In case of subclinical hypothyroidism, when TSH exceeds the threshold of 4.0 or 4.5 μIU/ml before IVF, LT4 replacement should be administered, while the same intervention might also be justified for women with TSH concentration more than 2.5 μIU/ml before IVF.
PURPOSE OF REVIEW: To summarize the evidence regarding the need to assess thyroid function in women undergoing ovarian stimulation as well as the need to intervene when thyroid function is suboptimal. RECENT FINDINGS: There is now evidence that ovarian stimulation can influence thyroid function not only via hyperestrogenism but also directly, since thyroid-related receptors are present in human granulosa cells and in the endometrium. Prospective and retrospective observational studies, as well as a few clinical trials, have been conducted in an effort to clarify the association between ovarian stimulation and thyroid function with controversial results. SUMMARY: The need of thyroid function screening with thyroid stimulating hormone (TSH) in infertile women attempting pregnancy is recognized by many international societies. Since TSH is a simple, cheap screening tool and levothyroxine (LT4) supplementation is an easy to apply, cheap and well tolerated intervention, universal thyroid screening in women undergoing IVF represents a reasonable policy. In case of subclinical hypothyroidism, when TSH exceeds the threshold of 4.0 or 4.5 μIU/ml before IVF, LT4 replacement should be administered, while the same intervention might also be justified for women with TSH concentration more than 2.5 μIU/ml before IVF.