Maternal Selenium and Iodine Nutritional Status and Perinatal Outcomes: A Scoping Review

Objectives: Selenium and iodine are essential trace elements whose requirements increase during pregnancy, jointly regulating thyroid function and placental homeostasis. While their individual effects have been extensively studied, the evidence on combined Se–I exposure and their underlying molecular interactions remains fragmented. This scoping review aimed to map the gestational dynamics of maternal selenium and iodine status, synthesize the evidence linking their independent and joint effects to perinatal outcomes, and summarize their potential interacting mechanisms. Methods: Following the PRISMA-ScR guidelines, PubMed, Web of Science, and Scopus were searched from 2016 to September 2026. Studies were eligible if they assessed maternal selenium and/or iodine status in pregnant women or mother–infant pairs and reported outcomes related to thyroid function, placental homeostasis, pregnancy complications, fetal development, or long-term offspring health. Data were charted using a standardized form and synthesized descriptively by nutrient exposure, biological axis, and outcome domain. Results: Of the 2198 records identified, 91 studies met the eligibility criteria (36 selenium-only, 53 iodine-only, and 2 combined Se–I). Evidence indicates that mild-to-moderate isolated or combined selenium and iodine deficiencies remain common in pregnancy and are associated with adverse perinatal outcomes. Mechanistic studies, largely from in vitro and animal models, support multi-level biological interactions between selenium and iodine in thyroid hormone activation, antioxidant pathways, and placental–maternal interface regulation. However, population-based evidence on combined exposure remains scarce, and no randomized controlled trial has evaluated the incremental clinical benefit of combined supplementation. Conclusions: Maternal selenium and iodine status are interrelated determinants of thyroid and placental function during pregnancy. Combined Se–I deficiency may be associated with a greater risk of adverse maternal and infant outcomes through overlapping and potentially interacting mechanisms; however, human evidence is insufficient to establish synergy. Future large-scale prospective cohorts and baseline-stratified randomized trials are urgently needed to establish an evidence base for status-guided integrated micronutrient screening and precision nutritional management during pregnancy.