Levothyroxine treatment for hypothyroidism in early pregnancy has inconsistent outcomes.
This study evaluated children’s cognitive function to ascertain the impact of preconception maternal hypothyroidism treatment on fetal neurodevelopment.
Prospective cohort study.
A single-center study conducted at a tertiary-care hospital.
Women were assigned to the before conception (BC) and after conception (AC; 8-14 gestational weeks) groups by timepoint of hypothyroidism diagnosis and treatment.
Levothyroxine treatment, adjusted based on results of monthly thyroid function test.
The Gesell Development Diagnosis Scale (GDDS; Chinese version) was used to assess neurocognitive development of children at 6, 12, and 24 months, with total score as the primary outcome.
Of the 466 participants, 187 and 279 were in the BC and AC groups, respectively. Both groups were comparable at baseline antenatal visit, except for a higher proportion of thyroid peroxidase (TPO) antibody-positive participants in the BC group (P&0.001). No significant intergroup differences were evident on GDDS neurodevelopmental assessment at 6, 12, and 24 months (P>0.05), except for unexpected slightly lower motor-ability (P=0.009) and total (P=0.026) scores at 12 months and adaptability at 24 months (P=0.037) in the BC group. Differences for motor ability (P&0.001) and total score (P=0.026) persisted on subgroup analysis for subclinical hypothyroidism, without significant differences in pregnancy and neonatal outcomes by severity and TPO status (P>0.05).
Preconception levothyroxine treatment did not induce significantly better cognitive outcomes in children up to age 2 than treatment initiated at 8-14 weeks of gestation.

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