Table 2.

Studies investigating the effect of severe iodine deficiency on pregnancy outcomes.

First author	Year	Country	n	Design	Median UIC (μg/L)	Outcomes assessed
Alvarez-Pedrerol et al. (39)	2009	Spain	657	Prospective study conducted on pregnant women. The association between thyroid hormones and UIC during the first and third trimesters, and birth weight was studied.	1st trimester: 95.0 3rd trimester: 104.0	1st trimester Iodine sufficiency (UIC 150–249 μg/L) vs. SID (UIC <50 μg/L) - Small for gestational age: OR 1.34 (95%CI 0.16–12.06) 1st trimester Mild iodine deficiency (UIC 100–149 μg/L) vs. SID (UIC <50 μg/L) - Small for gestational age: OR 0.37 (95%CI 0.03–5.36) 3rd trimester Iodine sufficiency (UIC 150–249 μg/L) vs. SID (UIC <50 μg/L) - Small for gestational age: OR 0.37 (95%CI 0.10–1.40) 3rd trimester Mild iodine deficiency (UIC 100–149 μg/L) vs. SID (UIC <50 μg/L) - Small for gestational age: OR 0.15 (95%CI 0.03–0.76)*
Dillon and Milliez (27)	2000	Senegal	4,980	Epidemiological survey on iodine deficiency disorders carried out in 1996-1997. Childbearing age women were questioned about their obstetric histories, including the numbers of miscarriages and stillbirths. Urine samples were collected, the iodine level measured.	43.0	SID (UIC <20 μg/L) vs. Iodine sufficiency (UIC 101–150 μg/L) - Reproductive failure: OR 3.64 (95%CI 2.92–4.55)*
Mills et al. (29)	2018	USA	501	Population-based prospective cohort study, monitored women who had discontinued contraception within 2 months to become pregnant; 329 became pregnant; had UIC measured on samples collected at enrollment, and were followed up to determine pregnancy outcomes.	112.8	SID (UIC <50 μg/L) vs. Iodine sufficiency (UIC 150–249 μg/L) - Pregnancy loss: HR 0.69 (95%CI 0.32–1.50)
Torlinska et al. (40)	2018	United Kingdom	3,140	Prospective study using data from the Avon Longitudinal Study of Parents and Children (ALSPAC). This study assessed whether iodine deficiency during pregnancy was associated with pregnancy/infant loss, or with other adverse pregnancy outcomes.	61.0	SID (UIC <50 μg/L) vs. Iodine sufficiency (UIC 150–249 μg/L) - Hypertensive disorders of pregnancy: OR 1.2 (95%CI 0.7–1.9) - Preeclampsia: OR 0.6 (95%CI 0.1–3.1) - Non-proteinuric gestational hypertension: OR 1.2 (95%CI 0.7–2.1) - Any glucose derangement: OR 1.1 (95%CI 0.5–2.3) - Gestational diabetes: OR 1.6 (95%CI 0.2–17.1) - Glycosuria: OR 0.7 (95%CI 0.2–2.0) - Hyperglycemia during pregnancy: OR 1.0 (95%CI 0.5–2.4) - Anemia during pregnancy: OR 1.2 (95%CI 0.5–2.5) - Anemia <14 days postpartum: OR 0.6 (95%CI 0.3–1.1) - Postpartum hemorrhage: OR 1.2 (95%CI 0.6–2.3) - Preterm delivery: OR 1.3 (95%CI 0.6–3.0) - Cesarean section: OR 0.6 (95%CI 0.3–1.3) - Assisted/breech delivery: OR 1.2 (95%CI 0.7–2.3) - Small for gestational age: OR 1.5 (95%CI 0.7–3.1) - Large for gestational age: OR 0.7 (95%CI 0.2–1.8)
Yang (41)	2018	China	2,347	Prospective study conducted on pregnant women. Urinary samples tested for iodine, serum samples tested for thyroid function, and questionnaires about demographic information were collected. Pregnancy outcomes were recorded and compared between different urinary iodine concentration and thyroid function groups.	203.8	Iodine sufficiency (UIC 150–249 μg/L) vs. SID (UIC <50 μg/L) - Cesarean delivery: OR 0.78 (95%CI 0.50–1.21) - Preterm delivery: OR 1.38 (95%CI 0.32–6.01) - Gestational diabetes: OR 0.32 (95%CI 0.03–3.23) - Preeclampsia: OR 0.12 (95%CI 0.01–0.87)* - Gestational hypertension: OR 0.49 (95%CI 0.13–1.89) - Placenta previa: OR 0.06 (95%CI 0.01–0.69)* - Abnormal amniotic fluid: OR 0.51 (95%CI 0.22–1.20) - Fetal distress: OR 0.10 (95%CI 0.02–0.64)* - Umbilical cord entanglement: OR 0.55 (95%CI 0.22–1.38) - Low birth weight: OR 3.73 (95%CI 0.69–20.28) - Macrosomia: OR 1.19 (95%CI 0.53–2.69) - Small for gestational age: OR 0.89 (95%CI 0.45–1.78)

Urinary iodine concentration (UIC), Severe iodine deficiency (SID), Odds ratio (OR), Hazard ratio (HR), Confidence interval (CI).

^*Statistically significant difference between groups.