Detection of thyroid dysfunction in early pregnancy: Universal screening or targeted high-risk case finding?

Context: Maternal subclinical hypothyroidism during pregnancy is associated with various adverse outcomes. Recent consensus guidelines do not advocate universal thyroid function screening during pregnancy but recommend testing high-risk pregnant women with a personal history of thyroid or other autoimmune disorders or with a family history of thyroid disorders. Objective: The objective of the study was to assess efficacy of the targeted high-risk case- finding approach in identifying women with thyroid dysfunction during early pregnancy. Design/ Setting: This was a single-center cohort study. Patients/ Outcome Measures: We prospectively analyzed TSH, free T-4 and free T-3 in 1560 consecutive pregnant women during their first antenatal visit ( median gestation 9 wk). We tested thyroperoxidase antibodies in 1327 ( 85%). We classified 413 women ( 26.5%), who had a personal history of thyroid or other autoimmune disorders or a family history of thyroid disorders, as a high- risk group. We examined whether testing only such a high- risk group would pick up most pregnant women with thyroid dysfunction. Results: Forty women ( 2.6%) had raised TSH (> 4.2 mIU/ liter). The prevalence of raised TSH was higher in the high- risk group [ 6.8 vs. 1% in the low- risk group, relative risk ( RR) 6.5, 95% confidence interval ( CI) 3.3 - 12.6, P < 0.0001]. Presence of personal history of thyroid disease ( RR 12.2, 95% CI 6.8 - 22, P < 0.0001) or other autoimmune disorders ( RR 4.8, 95% CI 1.3 - 18.2, P < 0.016), thyroperoxidase antibodies ( RR 8.4, 95% CI 4.6 - 15.3, P < 0.0001), and family history of thyroid disorders ( RR 3.4, 95% CI 1.8 - 6.2, P < 0.0001) increased the risk of raised TSH. However, 12 of 40 women with raised TSH ( 30%) were in the low- risk group. Conclusion: Targeted thyroid function testing of only the high- risk group would miss about one third of pregnant women with overt/ subclinical hypothyroidism.