BACKGROUND AND PURPOSE:

• Overt thyroid disease complicates 4% of pregnancy and is associated with adverse outcomes
• Little is known regarding the relationship between subclinical hypothyroidism (SCH) or thyroid autoimmunity and adverse pregnancy outcomes
• Plowden et al. (AJOG, 2017) examined whether there is an association between prepregnancy anti-thyroid antibodies/subclinical hypothyroidism and obstetric complications

METHODS:

• Secondary analysis of prospective cohort study from the Effects of Aspirin in Gestation and Reproduction (EAGeR) trial, a multicenter, double-blind, RCT on the effect of low-dose aspirin on live birth
  • 18-40 year-old women
  • 1-2 previous pregnancy losses
  • Analysis restricted to women with ongoing pregnancy > 20 weeks
• Prepregnancy levels of thyroid-stimulating hormone (TSH), free thyroxine fT4), thyroglobulin antibody (anti-TG), and thyroid peroxidase antibody (anti-TPO) were collected
  • Levels adjusted for age and body mass index
• Participants categorized in to 2 categories: TSH < 2.5 or ≥5 mIU/L
  • While SCH is usually defined as TSH above the normal range (4.5–5.0 mIU/L) with a normal fT4 level the National Academy of Clinical Biochemistry found that 95% of patients without any symptoms of thyroid dysfunction have a TSH level <2.5 mIU/L
• Adjusted for aspirin use because of association with pregnancy in women with single recent loss
• Primary outcomes
  • Preterm Birth (PTB), defined as delivery between 20w0d and 26w6d
  • GDM
  • Preeclampsia

RESULTS:

• Data was pooled from 1193 women
• There was no association between prepregnancy TSH < 2.5 vs ≥5 mIU/L and PTD, GDM or preeclampsia
• Among women with thyroid antibodies, there was no association between PTB, GDM or preeclampsia
• Authors took in to account whether PTB was medically indicated and there was still no association
• Among women with thyroid autoimmunity, there were no differences in PTB, GDM or preeclampsia including whether stratified by TSH level

CONCLUSION:

• Previous studies on SCH and preeclampsia show mixed results
  • Previous studies used higher TSH cut-offs and did not adjusted for BMI
• The results from this study are aligned with previous studies on SCH and GDM
• This study supports current ACOG recommendations that low-risk asymptomatic women should not be screened routinely for thyroid dysfunction or autoimmunity and patients with SCH and thyroid autoimmunity can be reassured

Learn More – Primary Sources:

Thyroid-stimulating hormone, anti–thyroid antibodies, and pregnancy outcomes

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