Undiagnosed hypothyroidism associated with adverse pregnancy outcomes

1. Women who screened positive for hypothyroidism but were not diagnosed with overt hypothyroidism on confirmatory testing were more likely to experience gestational hypertension and preeclampsia.

2. Women diagnosed with hypothyroidism who were treated had similar outcomes to euthyroid women.

Evidence Rating Level: 2 (Good)

Study Rundown: To meet the metabolic demands of pregnancy, a pregnant woman’s thyroid undergoes physiological changes to produce more T4-binding globulin, increasing total T4 and T3. In the case of hypothyroidism, these changes do not occur adequately and negatively affect fetal cognitive and bone development. Hypothyroidism is also associated with increased risk of pregnancy complications including preeclampsia, gestational hypertension, placental abruption, and perinatal morbidity and mortality. Prior studies have shown that targeted screening may miss cases while others demonstrated that universal screening does not improve pregnancy outcomes. Current recommendations are for targeted screening in the first trimester. In the present work, the authors compared maternal and neonatal outcomes between women who were euthyroid, those who were found to be hypothyroid on screening but not on confirmatory testing, and women who were diagnosed with hypothyroidism and treated. Results demonstrate that women with TSH >4.5 mU/L on initial testing but not on confirmatory testing were more likely to experience adverse outcomes. These findings suggest that treatment of women with TSH >4.5 mU/L, regardless of results of confirmatory testing, might decrease the incidence of maternal, peripartum and neonatal complications.

Strengths of the study included large population cohort and prospective data collection. Limitations include post hoc analysis, retrospective chart review and limited number of individuals with hypothyroidism, limiting the validity of the observed results. Further prospective studies or randomized controlled trials of treatment at different TSH levels are needed to determine the optimal hypothyroidism screening and treatment thresholds.

Click to read the study in AJOG

Relevant Reading: Hypothyroidism complicating pregnancy

In-Depth [prospective cohort]: This secondary analysis of a prospective population-based study evaluated the relationship between TSH screening thresholds and pregnancy outcomes in women with overt hypothyroidism who were treated (n = 47), women with unconfirmed hypothyroidism (n = 183), and women who were euthyroid (n = 24 584). Women with TSH >3.0 mU/L or free T4 <0.9 ng/dL were referred for confirmatory testing; TSH >4.5 mU/L and free T4 <0.76 ng/dL on repeat testing was classified as overt hypothyroidism. Outcomes of interest were gestational age, cesarean section, diabetes, gestational hypertension and severe preeclampsia.

Women who screened positive for hypothyroidism but did not meet criteria for overt hypothyroidism on confirmatory testing were more likely to experience gestational hypertension (p = 0.005) and preeclampsia (p = 0.001). Among this group, women with initial TSH >4.5 mU/L experienced increased odds for severe preeclampsia (OR 2.53, CI 1.41-4.54). Women who were diagnosed with overt hypothyroidism were treated and experienced similar pregnancy outcomes to euthyroid women.

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