Thyroid gland adjustment for fertility and during pregnancy

The correct functioning of the thyroid gland before and during pregnancy is essential for mother and child. Hyperthyroidism and overt hypothyroidism are both associated with adverse obstetric and neonatal outcomes. Whether subclinical hypothyroidism significantly affects the health of mother and child is controversially discussed and addressed in this manuscript. Currently the level of 2.5mU/l is used by many as the upper limit of the reference range of thyroid-stimulating hormone (TSH) for preconceptional adjustment in infertile patients. This is based on outdated guidelines that derived this limit from the also outdated upper reference limit for the first trimester; however, according to the latest guidelines of the American Thyroid Association the upper limit for TSH in pregnancy is 4.0-4.2mU/l. Therefore, the TSH level of 2.5mU/l is too low and can lead to overdiagnosis or even overtreatment. Moreover, there is no evidence of any significant adverse effect in the TSH range between 2.5 and 4.2mU/l. We recommend that TSH and TPO-Ab levels should be determined in every patient seeking fertility treatment. If both parameters are in the normal reference range of the laboratory, no treatment is necessary. If thyroid peroxidase antibodies (TPO-Ab) are positive and TSH above 2.5mU/l, consider treatment with levothyroxine. If TSH is outside the reference range, afurther work-up of the thyroid gland is necessary.