TABLE 2.

Association of dietary iron and fecundability among women planning a pregnancy in the Snart Foraeldre and PRESTO cohorts¹

	Pregnancies, n	Cycles at risk, n	Age adjusted FR (95% CI)	Multivariable2 FR (95% CI)	Mutually adjusted multivariable3 FR (95% CI)
Snart Foraeldre, n = 1693
Total iron, mg/d
<10	419	2348	1.00 (Ref.)	1.00 (Ref.)	—
10–11.9	606	3088	1.08 (0.97, 1.21)	1.10 (0.98, 1.24)	—
≥12	114	730	0.92 (0.76, 1.11)	0.98 (0.81, 1.20)	—
Heme iron, mg/d
<0.5	205	1125	1.00 (Ref.)	1.00 (Ref.)	1.00 (Ref.)
0.5–0.9	737	4025	1.02 (0.89, 1.17)	0.99 (0.86, 1.14)	0.99 (0.86, 1.14)
≥1.0	197	1016	1.05 (0.88, 1.25)	1.01 (0.85, 1.22)	1.00 (0.83, 1.20)
Nonheme iron, mg/d
<9	319	1801	1.00 (Ref.)	1.00 (Ref.)	1.00 (Ref.)
9–10.9	668	3495	1.07 (0.95, 1.21)	1.12 (0.99, 1.27)	1.12 (0.99, 1.27)
≥11	152	870	1.02 (0.85, 1.22)	1.11 (0.92, 1.34)	1.11 (0.92, 1.34)
PRESTO, n = 2969
Total iron, mg/d
<10	377	2832	1.00 (Ref.)	1.00 (Ref.)	—
10–11.9	608	4310	1.06 (0.94, 1.19)	0.98 (0.87, 1.10)	—
≥12	831	5258	1.16 (1.04, 1.30)	1.06 (0.94, 1.19)	—
Heme iron, mg/d
<0.5	776	5262	1.00 (Ref.)	1.00 (Ref.)	1.00 (Ref.)
0.5–0.9	837	5543	1.00 (0.91, 1.09)	1.03 (0.94, 1.12)	1.03 (0.94, 1.13)
≥1.0	203	1595	0.87 (0.76, 1.01)	1.01 (0.87, 1.17)	1.01 (0.87, 1.18)
Nonheme iron, mg/d
<9	293	2168	1.00 (Ref.)	1.00 (Ref.)	1.00 (Ref.)
9–10.9	573	4116	1.03 (0.91, 1.18)	0.96 (0.84, 1.09)	0.96 (0.84, 1.09)
≥11	950	6116	1.14 (1.01, 1.29)	1.01 (0.89, 1.14)	1.01 (0.89, 1.15)

¹FR, fecundability ratio.

²Adjusted for age, vocational training/education, BMI, physical activity, smoking, alcohol consumption, use of oral contraceptives, parity, cycle regularity and length, doing something to improve chances of conception, use of iron and vitamin C supplements, multivitamin use, dietary vitamin C (continuous), and total energy (continuous). The PRESTO models are also adjusted for race/ethnicity

³Also adjusted for dietary heme or nonheme iron intake, respectively.