Subclinical hypothyroidism and pregnancy

Pregnancy has a considerable impact on thyroid homeostasis that complicates the diagnosis of hypothyroidism. Pregnant women with overt hypothyroidism have appreciable maternal morbidity as well as perinatal morbidity and mortality. Treatment of such women has been shown to improve these outcomes. Controversy regarding the importance of identifying and treating women with subclinical hypothyroidism erupted after several reports have linked variously defined hypothyroidism with impaired neurodevelopment of the fetus. Frequently, these reports are erroneously considered as identifying women with subclinical hypothyroidism, when in fact, none of these studies specifically identified such women. To date, there have been no well-controlled, long-term studies on offspring of pregnant women with subclinical hypothyroidism as contemporaneously defined. Furthermore, these reports have led to conflicting and confusing position statements from several national entities as to whether all pregnant women should be screened for hypothyroidism and treatment prescribed for those found to have subclinical hypothyroidism. Importantly, there are also no published intervention trials specifically assessing the efficacy of such treatment to improve neurodevelopmental outcomes in offspring of women with subclinical hypothyroidism. It is acknowledged that obstetricians are under increasing pressure to screen for and treat pregnant women with subclinical hypothyroidism despite uncertainty that their offspring would benefit from therapy. National endocrine groups recommending such screening and treatment have emphasized that there is a need for large clinical trials to address these issues. Until such studies are completed, routine screening for and treatment of subclinical hypothyroidism during pregnancy is unwarranted and should be considered experimental.