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Grand Rounds

POSTAL Study Results: Does Levothyroxine Improve Pregnancy Outcomes in Women with Thyroid Autoantibodies Undergoing IVF?

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BACKGROUND AND PURPOSE:  

  • Overt hypothyroidism is associated with increased risk of spontaneous miscarriage 
  • Most hypothyroidism in reproductive age women is caused by ‘thyroid autoimmunity’ defined as the presence of  
    • Thyroid autoantibodies 
    • Antithyroperoxidase antibody 
    • Antithyroglobulin antibody 
  • Some previous research suggests increased miscarriage among women with thyroid autoantibodies, including in the setting of IVF  
  • Conflicting data as to whether levothyroxine impacts miscarriage rates when thyroid function is intact but autoantibodies are present  
  • Wang et al. (JAMA, 2017) sought to determine whether levothyroxine treatment improves pregnancy outcomes among women undergoing in vitro fertilization and embryo transfer (IVF-ET) who had otherwise normal thyroid function but tested positive for thyroid autoantibodies  

METHODS:  

  • Open-label, randomized clinical trial  
  • Pregnancy Outcomes Study in Euthyroid Women With Thyroid Autoimmunity After Levothyroxine (POSTAL) study conducted over the 4.5-year study period)  
  • Patients: Women referred for their first or second fresh IVF-ET cycles 
    • 23-40 years of age 
    • BMI ≤35 
    • No known endocrinological disorders or ≥2 miscarriages  
    • Normal thyroid function (TSH normal) but positive for antithyroperoxidase antibody  
  • Women were randomized to   
    • Intervention group:  25 25-μg/d or 50-μg/d dose of levothyroxine at study initiation that was titrated according to the level of TSH during pregnancy  
    • Control group: Not administered levothyroxine 
  • Primary outcome  
    • Miscarriage rate: Pregnancy loss before 28 weeks of gestation 
  • Secondary outcomes  
    • Clinical intrauterine pregnancy rate: Fetal cardiac activity seen at sonography observation on the 30th day after the embryo transfer 
    • Live-birth rate: At least 1 live birth after 28 weeks of gestation  

RESULTS:

  • 565 women had IVF-ET and completed the study 
    • Mean age was 31.6 years   
  • Miscarriage rates  
    • 10.3% in the intervention group and 10.6% in the control group  
      • Absolute rate difference (RD) of -0.34% (95% CI, -8.65% to 8.12%)  
  • Clinical intrauterine pregnancy rates  
    • 35.7% in the intervention group and 37.7% in the control group  
    • Absolute RD of -2.00% (95% CI, -9.65% to 5.69%)  
  • Live-birth rates  
    • 31.7% in the intervention group and 32.3% in the control group  
      • Absolute RD of -0.67% (95% CI, -8.09% to 6.77%)  
  • Subgroup analysis on TSH levels ≥2.5mIU/L and ≥4.0 mIU/L  
    • No levothyroxine benefit found 

CONCLUSION:  

  • Authors recognize limitations of this study, including lack of placebo, however, outcomes (e.g., miscarriage) could not be impacted by the investigator  
  • Levothyroxine treatment did not impact miscarriage or live-birth rates for women undergoing IVF-ET with normal thyroid function and presence of antithyroperoxidase antibody  
  • This data supports the American Thyroid Association and Endocrine Society guidelines  
  • There are ongoing trials to assess benefit of levothyroxine treatment in other non-IVF settings 

Learn More – Primary Sources:   

Effect of Levothyroxine on Miscarriage Among Women With Normal Thyroid Function and Thyroid Autoimmunity Undergoing In Vitro Fertilization and Embryo Transfer: A Randomized Clinical Trial

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Related ObG Topics:

Should Levothyroxine be Used to Treat Subclinical Hypothyroidism?
How Do Thyroid Levels Impact Life Expectancy?
Subclinical Hypothyroidism and Pregnancy Outcome – Is There a Relationship?

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