Low maternal iodine status in early pregnancy gives lower IQ

Objectives:
Low maternal free thyroxine (FT4) has been associated with poor child neurodevelopment in some single-centre studies. Evidence remains scarce for potential adverse effects of high FT4 and whether associations differ in countries with a different iodine status. Therefore, this review article has been conducted.

Is there an association between maternal thyroid function in early pregnancy and child neurodevelopment in countries with a different iodine status?

Study design:
This review article included individual-participant data compromising 9,036 mother-child pairs from 3 prospective population-based birth cohorts: INMA (Spain), Generation R (The Netherlands) and ALSPAC (United Kingdom).

Main outcomes were child non-verbal IQ at 5-8 years of age, verbal IQ at 1.5-8 years of age, and autistic traits within the clinical range at 5-8 years of age.

Results and conclusions:
The investigators found low maternal free thyroxine 2.5th percentile was associated with a significantly 3.9 [95% CI = -5.7 to -2.2] point lower non-verbal IQ.

The investigators found low maternal free thyroxine 2.5th percentile was associated with a significantly 2.1 [95% CI = -4.0 to -0.1] point lower verbal IQ.

The investigators found a suggestive association of hypothyroxinemia with a higher risk of autistic traits.

The investigators found low maternal free thyroxine >97.5th percentile was associated with a significantly 1.9 [95% CI = 1.0 to 3.4] fold higher risk of autistic traits.

The investigators found no independent associations with thyrotropin.

The investigators concluded that low maternal free thyroxine is consistently associated with lower IQ across cohort studies. Further studies should replicate the findings of autistic traits and investigate the potential modifying role of maternal iodine status. Free thyroxine seems a reliable marker of fetal thyroid state in early pregnancy, regardless of the type of immunoassay.

Original title:
Thyroid Function in Early Pregnancy, Child IQ, and Autistic Traits: a Meta-analysis of Individual-participant Data by Levie D, Korevaar T, [...], Guxens M.

Link:
https://www.ncbi.nlm.nih.gov/pubmed/29757392

Additional information of El Mondo:
Find more information/studies on food fortification/malnutrition, iodine, pregnancy and study design/meta-analysis/significant right here.