Insufficient maternal iodine intake is associated with subfecundity, reduced foetal growth, and adverse pregnancy outcomes in the Norwegian Mother, Father and Child Cohort Study.

• Severe iodine deficiency impacts fertility and reproductive outcomes. The potential effects of mild-to-moderate iodine deficiency are not well known. The aim of this study was to examine whether iodine intake was associated with subfecundity (i.e. >12months trying to get pregnant), foetal growth, and adverse pregnancy outcomes in a mild-to-moderately iodine-deficient population.We used the Norwegian Mother, Father and Child Cohort Study (MoBa) and included 78,318 pregnancies with data on iodine intake and pregnancy outcomes. Iodine intake was calculated using an extensive food frequency questionnaire in mid-pregnancy. In addition, urinary iodine concentration was available in a subsample of 2795 pregnancies. Associations were modelled continuously by multivariable regression controlling for a range of confounding factors.The median iodine intake from food was 121μg/day and the median urinary iodine was 69μg/L, confirming mild-to-moderate iodine deficiency. In non-users of iodine supplements (n=49,187), low iodine intake (<100-150μg/day) was associated with increased risk of preeclampsia (aOR=1.14 (95% CI 1.08, 1.22) at 75 vs. 100μg/day, p overall <0.001), preterm delivery before gestational week 37 (aOR=1.10 (1.04, 1.16) at 75 vs. 100μg/day, p overall=0.003), and reduced foetal growth (-0.08 SD (-0.10, -0.06) difference in birth weight z-score at 75 vs. 150μg/day, p overall <0.001), but not with early preterm delivery or intrauterine death. In planned pregnancies (n=56,416), having an iodine intake lower than ~100μg/day was associated with increased prevalence of subfecundity (aOR=1.05 (1.01, 1.09) at 75μg/day vs. 100μg/day, p overall=0.005). Long-term iodine supplement use (initiated before pregnancy) was associated with increased foetal growth (+0.05 SD (0.03, 0.07) on birth weight z-score, p<0.001) and reduced risk of preeclampsia (aOR 0.85 (0.74, 0.98), p=0.022), but not with the other adverse pregnancy outcomes. Urinary iodine concentration was not associated with any of the dichotomous outcomes, but positively associated with foetal growth (n=2795, p overall=0.017).This study shows that a low iodine intake was associated with restricted foetal growth and a higher prevalence of preeclampsia in these mild-to-moderately iodine-deficient women. Results also indicated increased risk of subfecundity and preterm delivery. Initiating iodine supplement use in pregnancy may be too late.

Ämnesord

MEDICIN OCH HÄLSOVETENSKAP  -- Klinisk medicin -- Reproduktionsmedicin och gynekologi (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Clinical Medicine -- Obstetrics, Gynaecology and Reproductive Medicine (hsv//eng)

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