Table 1.

Descriptive Characteristics of the Study Population (n = 2910 Pregnancies)

Study sample/pregnancies, n	2910
Maternal age at delivery (years), mean (SD)	30.3 (4.2)
Gestational age at sampling (weeks), mean (SD)	18.5 (1.3)
Prepregnancy BMI (kg/m2), mean (SD)	23.9 (4.0)
Parity, %
0	52
1	33
2 or more	14
Maternal education, %
≤12 years	26
13–16 years	47
>16 years	25
Other/missing	2.1
Married/cohabitant, %	98.4
In vitro fertilization, %	2.2
Smoking in pregnancy, %
Occasionally	14
Daily	3.8
Chronic illness, %	8.9
Household income, %
Low	26
Medium	43
High	29
Missing	1.9
Iodine from food (μg/day), median (IQR)	121 (90, 160)
UIC (μg/L), median (IQR)	68 (35, 116)
Urinary creatinine (g/L), median (90% range)	0.76 (0.17, 1.92)
UIC (μg/g creatinine), median (IQR)	91 (61, 139)
UIC∼Cr (μg/L), median (IQR)	74 (55, 105)
UIC, %
≥150 μg/L (sufficienta)	14
0–150 μg/L (insufficienta)	86
0–100 μg/L	68
0–50 μg/L	37
Plasma FT4 [pmol/L], median [95% range]	12.6 [10.3, 15.7]
Plasma FT3 [pmol/L], median [95% range]	4.9 [4.0, 6.0]
Plasma TSH [mU/L], median [95% range]	1.2 [0.4, 2.9]
Plasma TPOAb positive,b %	8.1
Plasma TgAb positive,b %	7.9
Plasma ferritin (ng/mL), median (IQR)	33 (20, 56)
Empty iron stores (P-Fe <12 ng/mL), %	9.0
Low iron stores (P-Fe 12–29.9 ng/mL), %	35
Whole blood selenium (μg/L), median (IQR)	102 (89, 117)
Low selenium (<80 μg/L), %	10

^aPopulation median UIC <150μg/L is the recommended cutoff for defining inadequate iodine intake in pregnancy by the World Health Organization.

^bAntibody positivity was defined as values above the 92nd percentile (>6.6 IU/mL for TPOAb and >7 IU/mL for TgAb).

IQR, interquartile range; SD, standard deviation; TgAb; thyroglobulin antibodies; TPOAb, thyroid peroxidase antibodies; UIC, urinary iodine concentration; UIC∼Cr, UIC adjusted for creatinine.