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Preconception vs. postconception iodine supplementation: Effect on thyroglobulin decline in a Québec pregnancy cohort
Jesse Bertinato1, Philip Griffin1, Marc Duciaume1
1Nutrition Research Division, Bureau of Nutritional Sciences, Food and Nutrition Directorate, Health Products and Food Branch, Health Canada, Ontario, Ottawa, Canada.
Summary
Iodine supplementation during pregnancy, even if started after conception, may help normalize thyroid function. This study found a greater reduction in thyroglobulin levels in women who began supplementation postconception, indicating potential benefits for thyroid status.
Area of Science:
- Obstetrics and Gynecology
- Endocrinology
- Nutritional Science
Background:
- Iodine is crucial during pregnancy to prevent infant cognitive impairment.
- The American Thyroid Association recommends 150 µg/day iodine supplementation starting 3 months before conception.
- Only 36% of women in a Québec cohort started iodine supplementation before conception.
Purpose of the Study:
- To compare the effect of pre- vs. postconception iodine supplementation on long-term thyroid status in a Québec pregnancy cohort.
- To utilize thyroglobulin (Tg) as a sensitive marker of iodine status.
- To assess iodine sufficiency and thyroid hormone levels (TSH, FT4).
Main Methods:
- Serum Tg, TSH, and FT4 levels were measured in pregnant women at two time points (T1: 10.1-14.9 weeks; T2: 19.7-24.9 weeks).
- Participants were divided into pre- and postconception iodine supplementation groups.
- Generalized Linear Mixed Models were used for group comparisons.
Main Results:
- 64% of 474 participants started supplementation after conception; iodine dose and usage were similar between groups.
- Thyroglobulin (Tg) levels declined significantly from T1 to T2 in both groups (p < 0.0001).
- The postconception group showed a significantly greater Tg decline (p = 0.008), suggesting normalization of thyroid stimulation from prior deficiency. TSH and FT4 levels did not differ, and hypothyroidism prevalence was low.
Conclusions:
- Starting iodine supplementation after conception may help normalize thyroid stimulation related to iodine deficiency.
- The observed greater Tg reduction in the postconception group indicates a positive impact on thyroid function.
- While preconception supplementation is ideal, postconception intake appears beneficial for maternal iodine status.
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