During the past decades, observational studies have demonstrated a relationship between thyroid dysfunction in pregnancy and a range of adverse outcomes in both mother and offspring. However, results from the few randomized trials of screening for thyroid dysfunction in pregnant women have not shown any benefit for women or their children. Before implementing screening in pregnant women at population level, randomized trials are needed to show that screening with subsequent intervention is effective for mothers or children. Here, we review the literature and argue that the findings from existing trials are not conclusive. Until such conclusive evidence from randomized trials is available, the best advice to the clinician is to screen only high-risk pregnant women. Such women, for example those with symptoms or a history of thyroid problems, should be screened using trimester-specific reference ranges for thyroid stimulating hormone (TSH) levels. We recommend new prospective randomized trials that combine different thyroid parameters as the screening tool, apply trimester-specific ranges for thyroid hormones and examine whether screening and intervention during the first trimester of pregnancy will improve neuropsychological outcomes in the offspring.
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