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Table 3 Use of iodine-containing supplements and pregnancy and birth outcomes

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

  Number Crude models   Adjusted modelsa   Restricted controlsb
   Odds ratio (95% CI) p value Odds ratio (95% CI) p value Odds ratio (95% CI)
Intrauterine death 270/78,318 (0.34%)      
 Any iodine supplement use GW 0–20 29,131 0.80 (0.62, 1.03) 0.089 0.78 (0.61, 1.02) 0.071 0.96 (0.64, 1.45)
 First report of iodine supplement
  Never (non-supplement user) 49,187 (13,451b) 1 (ref.)   1 (ref.)   1 (ref.)
  Before pregnancyc 7477 0.79 (0.51, 1.23) 0.30 0.76 (0.48 1.19) 0.23 0.92 (0.53, 1.62)
  GW 0–12 7149 0.94 (0.62, 1.42) 0.77 0.92 (0.60, 1.40) 0.70 1.11 (0.63, 1.94)
  GW > 12 5253 0.77 (0.45, 1.30) 0.32 0.76 (0.45, 1.29) 0.31 0.78 (0.38, 1.60)
Preeclampsia 2936/78,318 (3.8%)      
 Any iodine supplement use GW 0–20 29,131 0.98 (0.91, 1.06) 0.64 0.93 (0.86, 1.01) 0.098 0.94 (0.84, 1.06)
 First report of iodine supplement
  Never (non-supplement user) 49,187 (13,451b) 1 (ref.)   1 (ref.)   1 (ref.)
  Before pregnancyc 7477 0.88 (0.77, 1.01) 0.067 0.85 (0.74, 0.98) 0.022 0.84 (0.71, 1.00)
  GW 0–12 7149 1.05 (0.92, 1.19) 0.48 0.96 (0.84, 1.10) 0.58 0.97 (0.82, 1.14)
  GW > 12 5253 0.99 (0.86, 1.15) 0.93 0.93 (0.80, 1.08) 0.35 0.91 (0.76, 1.11)
Preterm delivery (< GW 37) 3889/77,995 (5.0%)      
 Any iodine supplement use GW 0–20 29,014 1.00 (0.93, 1.07) 0.98 0.97 (0.91, 1.04) 0.42 1.07 (0.96, 1.18)
 First report of iodine supplement       
  Never (non-supplement user) 48,981 (13,405b) 1 (ref.)   1 (ref.)   1 (ref.)
  Before pregnancyc 7445 1.07 (0.96, 1.20) 0.21 1.05 (0.94, 1.18) 0.35 1.18 (1.03, 1.36)
  GW 0–12 7126 1.02 (0.91, 1.14) 0.70 0.99 (0.88, 1.11) 0.82 1.08 (0.94, 1.25)
  GW > 12 5230 1.02 (0.90, 1.17) 0.71 0.99 (0.87, 1.13) 0.86 1.04 (0.89, 1.23)
Early preterm delivery (< GW 32) 612/77,995 (0.78%)      
 Any iodine supplement use GW 0–20 29,014 0.82 (0.69, 0.97) 0.020 0.80 (0.67, 0.95) 0.010 0.82 (0.64, 1.05)
 First report of iodine supplement
  Never (non-supplement user) 48,981 (13,405b) 1 (ref.)   1 (ref.)   1 (ref.)
  Before pregnancyc 7445 0.94 (0.72,1.24) 0.67 0.94 (0.71, 1.24) 0.66 0.98 (0.71, 1.38)
  GW 0–12 7126 0.83 (0.62,1.12) 0.22 0.80 (0.60, 1.08) 0.14 0.73 (0.51, 1.08)
  GW > 12 5230 0.61 (0.41, 0.90) 0.014 0.59 (0.40, 0.87) 0.008 0.62 (0.39, 0.98)
Spontaneous preterm delivery (< GW 37) 2211/76,313 (2.8%)      
 Any iodine supplement use GW 0–20 28,406 1.03 (0.95, 1.13) 0.45 1.00 (0.91, 1.09) 0.93 1.09 (0.95, 1.25)
 First report of iodine supplement
  Never (non-supplement user) 47,907 (13,196b) 1 (ref.)   1 (ref.)   1 (ref.)
  Before pregnancyc 7273 1.08 (0.94, 1.25) 0.28 1.07 (0.92, 1.24) 0.39 1.20 (1.00, 1.44)
  GW 0–12 6977 1.08 (0.93, 1.25) 0.31 1.02 (0.88, 1.19) 0.75 1.12 (0.93, 1.35)
  GW > 12 5123 1.09 (0.93, 1.29) 0.29 1.04 (0.88, 1.23) 0.65 1.12 (0.91, 1.38)
   Beta (95% CI)   Beta (95% CI)   Beta (95% CI)
Birth weight 78,210      
 Any iodine supplement use GW 0–20 29,091 − 11.0 (− 19.4, − 2.7) 0.009 13.6 (5.6, 21.7) 0.001 3.3 (−8.3, 14.8)
 First report of iodine supplement
  Never (non-supplement user) 49,119 (13,435b) 0 (ref.)   0 (ref.)   0 (ref.)
  Before pregnancyc 7462 − 5.1 (− 19.1, 8.9) 0.48 16.3 (2.7, 29.9) 0.019 7.5 (− 9.0, 23.9)
  GW 0–12 7139 − 12.4 (− 26.4, 1.6) 0.084 19.6 (6.0, 33.1) 0.005 9.7 (− 6.8, 26.2)
  GW > 12 5248 − 11.7 (− 27.7, 4.3) 0.15 16.8 (1.4, 32.2) 0.033 12.0 (− 6.5, 30.4)
Birth weightz-score 77,949      
 Any iodine supplement use GW 0–20 28,998 − 0.03 (− 0.04, −  0.01) 0.001 0.03 (0.01, 0.04) < 0.001 0.01 (− 0.01, 0.03)
 First report of iodine supplement
  Never (non-supplement user) 48,951 (13,393b) 0 (ref.)   0 (ref.)   0 (ref.)
  Before pregnancyc 7439 0.00 (−0.02, 0.03) 0.88 0.05 (0.03, 0.07) < 0.001 0.04 (0.01, 0.07)
  GW 0–12 7121 − 0.03 (− 0.05, − 0.00) 0.043 0.04 (0.02, 0.07) < 0.001 0.03 (0.00, 0.06)
  GW > 12 5229 − 0.04 (− 0.07, − 0.02) 0.002 0.02 (− 0.01, 0.05) 0.13 0.01 (− 0.02, 0.05)
   Odds ratio (95% CI)   Odds ratio (95% CI)   Odds ratio (95% CI)
SGA 7637/77,949 (9.8%)      
 Any iodine supplement use GW 0–20 28,998 1.01 (0.96, 1.06) 0.83 0.91 (0.87, 0.96) < 0.001 0.95 (0.88, 1.02)
 First report of iodine supplement
  Never (non-supplement user) 48,951 (13,393b) 1 (ref.)   1 (ref.)   1 (ref.)
  Before pregnancyc 7439 0.97 (0.89, 1.06) 0.49 0.89 (0.82, 0.97) 0.009 0.91 (0.82, 1.01)
  GW 0–12 7121 0.98 (0.90, 1.07) 0.70 0.88 (0.80, 0.95) 0.003 0.91 (0.82, 1.02)
  GW > 12 5229 1.04 (0.94, 1.14) 0.44 0.93 (0.84, 1.02) 0.139 0.95 (0.85, 1.07)
LGA 7539/77,949 (9.7%)      
 Any iodine supplement use GW 0–20 28,998 0.92 (0.88, 0.97) 0.002 1.03 (0.98, 1.08) 0.31 1.02 (0.95, 1.10)
 First report of iodine supplement
  Never (non-supplement user) 48,951 (13,393b) 1 (ref.)   1 (ref.)   1 (ref.)
  Before pregnancyc 7439 1.00 (0.92, 1.08) 0.92 1.10 (1.01, 1.19) 0.034 1.08 (0.97, 1.19)
  GW 0–12 7121 0.89 (0.82, 0.97) 0.011 1.03 (0.94, 1.12) 0.57 1.02 (0.92, 1.14)
  GW > 12 5229 0.88 (0.80, 0.97) 0.014 1.01 (0.91, 1.12) 0.89 1.01 (0.90, 1.14)
  1. aModels were adjusted for maternal age, BMI, parity, education, smoking in pregnancy, fibre intake, chronic illness, in vitro fertilization, folic acid supplement within the interval from 4 weeks before to 8 weeks after conception (only for intrauterine death), child sex (only for unstandardized birth weight), and vitamin D (only for preeclampsia)
  2. bAdjusted associations restricting the reference group (non-users) to participants who reported use of one or more multivitamin/multimineral supplements in the food frequency questionnaire, but not any containing iodine
  3. cOne to 26 weeks before conception