Preconception Care to Optimize Pregnancy Outcomes

To the Editor

In the recent JAMA Insights article¹ about the utility of the preconception care period as an opportunity to optimize pregnancy outcomes, the authors discussed various health conditions that may affect pregnancy outcomes and mentioned that daily allowances should be met for micronutrients including folate, iron, vitamin B₁₂, and vitamin D. We would like to highlight the importance of another micronutrient in pregnant women, iodine.

Iodine is an essential micronutrient used in the synthesis of thyroid hormone, which is critical for normal fetal development. Increased maternal thyroid hormone production, increased maternal renal iodine clearance, and placental transfer of iodine for fetal thyroid hormone production later in gestation lead to an increased iodine requirement in pregnancy. Thus, pregnant women have an increased risk of iodine deficiency, which has been associated with adverse obstetric outcomes such as pregnancy loss, preterm birth, low birth weight, and adverse child neurodevelopmental outcomes.² Consequently, the Institute of Medicine and the World Health Organization recommend a higher iodine intake for pregnant women compared with nonpregnant women. The US Department of Agriculture also emphasizes importance of adequate iodine intake during pregnancy in the current dietary guidelines.³

Despite global efforts over recent decades, iodine deficiency remains a leading cause of maternal hypothyroidism worldwide, and two-thirds of countries with available data report inadequate iodine intake in pregnant women.⁴ Although the general US population is considered to be iodine sufficient, pregnant women in the US are mildly iodine deficient based on a 2007–2014 assessment.⁵ Thus, the American Thyroid Association, the Endocrine Society, and the American Academy of Pediatrics all recommend that women planning pregnancy or who are pregnant or breastfeeding should take a 150-μg iodine supplement daily.