Knowledge regarding the repercussions of maternal thyroid disease during pregnancy has increased tremendously during the past few years. However, the association between thyroid disease and adverse outcomes has been mainly studied in observational cohorts with cross-sectional thyroid function testing. A few randomized trials have been published evaluating the effectiveness of screening and treating for maternal subclinical hypothyroidism, but their results have generally shown little or no effect in preventing adverse outcomes. The effect of levothyroxine treatment on cognitive development in the child after maternal subclinical hypothyroidism is currently under study in an ongoing placebo-controlled randomized trial conducted in the USA by the Eunice Kennedy Shriver National Institute of Child Health and Human Development and expected to be completed in 2015. The secondary outcomes of the trial include studying the effects of adequate treatment of maternal subclinical hypothyroidism on pregnancy and neonatal outcomes as well, including risk of preterm delivery, preeclampsia, fetal growth and stillbirth. This study will also provide new data on the natural history of subclinical hypothyroidism during pregnancy, as the study will have longitudinal follow-up throughout pregnancy and postpartum. If treatment proves effective in this trial, routine screening of all pregnant women (or women planning pregnancy) should be considered, as subclinical hypothyroidism is often missed in risk-factor-based screenings. Despite this ongoing study, there still is a dire need for prospective studies with longitudinal data collection to help clarify the natural history of thyroid function and dysfunction during pregnancy.
Expert Rev Endocrinol Metab. 2013;8(6):537-547. © 2013 Expert Reviews Ltd.