Table 3.

Multivariate adjusted relative risks of ovulatory infertility by frequency of multivitamins among non-users of contraception.

	Frequency of Multivitamin Use
Subgroup	Never	≤ 2 /wk	3 – 5 / wk	≥ 6 / wk	P trend *
All participants
Cases / non-cases	224 / 10,926	32 / 1,808	52 / 3,796	127 / 9,783
Relative risk (95% CI) †	1.00 (referent)	0.88 (0.60, 1.28)	0.69 (0.51, 0.95)	0.59 (0.46, 0.75)	<0.001
Not using any contraceptive method
Cases / non-cases	128 / 3,872	16 / 667	25 / 1,548	71 / 4,997
Relative risk (95% CI) †	1.00 (referent)	0.72 (0.42, 1.24)	0.50 (0.32, 0.78)	0.41 (0.29, 0.56)	<0.001
Not using hormonal contraception ‡
Cases / non-cases	184 / 8,760	25 / 1,524	49 / 3,251	113 / 8,822
Relative risk (95% CI) †	1.00 (referent)	0.80 (0.52, 1.22)	0.75 (0.54, 1.04)	0.57 (0.44, 0.73)	<0.001
Not using barrier methods §
Cases / non-cases	172 / 6,355	23 / 998	29 / 2,201	88 / 6,190
Relative risk (95% CI) †	1.00 (referent)	0.82 (0.53, 1.29)	0.49 (0.33, 0.73)	0.49 (0.37, 0.65)	<0.001

^*Calculated with the median frequency of use in each category as a continuous variable.

^†Adjusted for age (continuous), calendar time (4 two-year intervals), total energy intake (continuous), body mass index (<20, 20–24.9, 25–29.9, ≥30 and missing), parity (0, 1, ≥2 and missing), smoking history (never, past 1–4 cig/day, past 5–14 cig/day, past 15–24 cig/day, past ≥ 25 cig/day or unknown amount, current 1–4 cig/day, current 5–14 cig/day, current 15–24 cig/day and current ≥ 25 cig/day or unknown amount), physical activity (<3 MET-h/wk, 3–8.9 MET-h/wk, 9–17.9 MET-h/wk, 18–26.9 MET-h/wk, 27–41.9 METh/wk, ≥ 42 MET-h/wk and missing), and intakes of alcohol (no intake, < 2 g/day, 2–4.9 g/day, ≥ 5 g/day), coffee (<1 serving/month, 1 serving/month, 2–6 servings/week, 1 serving/day, 2–3 servings/day, ≥ 4 servings/day) major types of fatty acids and protein. The model including all participants regardless of recent contraception also includes terms for recency of contraceptive use (current user, never user, past user 0–23 months ago, past user 24–47 months ago, past user 48–71 months ago, past user 72–95 months ago, past user 96–119 months ago, past user ≥ 120 months ago and missing).

^‡Oral contraceptives and injected or implantable progestins

^§Condoms, diaphragms or cervical caps.