Table II.

Characteristics of women in the Collaborative Perinatal Project and their association with time to pregnancy. Women in the Collaborative Perinatal Project were enrolled at 12 study centers in the United States from 1959–1965.

Characteristic	All Women (N=7327)	Time to pregnancy ≤ 3 months (n=3801)	Time to pregnancy> 3 months (n=3526)	Age-Adjusted Fecundability Odds Ratio†
	% or Median(Q1, Q3) ‡	% or Median (Q1, Q3)	% or Median (Q1, Q3)	FOR	95% CI
Prepregnancy BMI*	21.4 (19.6, 23.7)	21.2 (19.6, 23.3)	21.8 (19.8, 24.2)
Under-weight	12	12	12	0.94	0.86, 1.03
Optimal weight	71	73	69	1	--
Over-weight	13	11	14	0.84	0.77, 0.92
Obese	5	4	5	0.72	0.63, 0.83
Median Age (years)	23 (20, 27)	22 (20, 26)	24 (21, 28)	0.95	0.94, 0.96
Smokers (%)	45	44	47	0.91	0.86, 0.96
Race (%)
White	63	68	57	1	--
Non-white	37	32	43	0.65	0.62, 0.70
Prior Pregnancies (%)
0	36	39	33	1	--
1	30	31	30	0.98	0.91, 1.05
2+	34	30	37	1.04	0.97, 1.13
Prior Miscarriage
0	79	82	77	1	--
1	15	14	17	0.96	0.88, 1.04
2+	6	4	6	0.97	0.86, 1.11
Irregular cycles (%)	8	7	9	0.82	0.74, 0.91
Occupation (%)
Never worked	12	12	13	1	--
White collar	44	49	39	1.47	1.34, 1.61
Blue collar	44	39	48	1.02	0.93, 1.11
Education
Elementary	16	12	19	0.44	0.40, 0.49
Less than HS	33	32	33	0.54	0.49, 0.59
HS	33	33	33	0.63	0.58, 0.68
More than HS	19	23	14	1	--

^*BMI = body mass index; categorized into underweight (<18.5 kg/m²), normal weight (18.5 kg/m²–24.9 kg/m²), overweight (25.0 kg/m²–29.9 kg/m²), and obese (≥30.0 kg/m²).

^†Cox discrete time survival analysis used to model time-to-pregnancy, fecundability odds ratios and 95 percent (%) confidence interval (CI) reported

^‡% = percent, Q1 = quartile 1, Q3 = quartile 3, FOR = fecundability odds ratio, CI = confidence interval