BACKGROUND AND PURPOSE:

• Thyroid hormone replacement therapy (THRT) is recommended during pregnancy for women with hypothyroidism and (according to some professional societies) subclinical hypothyroidism
• It remains unclear if THRT improves cognitive function and language abilities in offspring
• Frank et al. (JAMA Network Open, 2019) assessed associations between prenatal THRT and communication skills in exposed children

METHODS:

• Prospective population-based cohort study
  • Norwegian Mother, Father and Child Cohort Study (MoBa)
  • Links to several nationwide registries including Norwegian Patient Registry (NPR)
• Participants
  • Singleton pregnancies resulting in a live-born infant
  • Child follow up ongoing
• Mother-child pairs were categorized into 3 mutually exclusive groups
  • THRT exposure during pregnancy (based on dispensed prescription records)
  • Unexposed to THRT during pregnancy (population comparison – no hypothyroidism)
  • Mothers initiating THRT after delivery (incident postnatal hypothyroidism)
• Data analysis
  • Hazard ratio (HR) was calculated for language impairment diagnosis
  • Standardized mean score (β) was calculated for parent-reported symptoms of language and communication deficits
• Primary outcomes
  • Diagnosis of language and speech impairment
    • NPR sample: Based on diagnoses
    • MoBa sample: Based on parental self-completed questionnaires at follow-up until 8-years of age

RESULTS:

• NPR sample: 53,862 mother-child pairs
  • Mean age: 30.4 years
  • Exposure to THRT: 2.2%
• MoBa sample: 23,686 mother-child pairs
  • Mean age, 30.8 years
  • Exposure to THRT: 2.2%
• NPR sample: There was no significant association between language and speech impairment diagnosis and prenatal THRT exposure (NPR database)
  • Compared to unexposed group
    • Adjusted HR 0.75 (95% CI, 0.38 to 1.43)
  • Compared to the THRT after delivery group
    • Adjusted HR 0.63 (95% CI, 0.26 to 1.53)
• MoBa study sample: There were no significant differences in mean language scores vs unexposed group reported by parents
  • Pronunciation problems:  Mean difference −0.01 (95% CI, −0.10 to 0.08)
  • Autism: Mean difference 0.05 (95% CI, −0.03 to 0.13)

CONCLUSION:

• At 8 years of age, there was no difference in language and communication skills between children born to women taking THRT vs a normal control group  
  • Study looked at outcomes based on diagnoses as well as parental questionnaires
• The results of this study support continuing recommendations for hypothyroidism treatment during pregnancy
• Future studies should perform a comparison to a disease group (children from untreated mothers)

Learn More – Primary Sources:

Maternal Thyroid Hormone Replacement Therapy Exposure and Language and Communication Skills of Offspring at 8 Years of Age

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