Table 1. Characteristics of participating case and control women.

Characteristic	Cases n=33 (%)		Controls n=66 (%)		P-valuea
Maternal age (years)
<20	9	27.2	5	7.6	0.002
20-24	17	51.5	24	36.4
25-29	6	18.2	21	31.8
≥30	1	3.0	16	24.2
Race/Ethnicity
White, non-Hispanic	30	90.9	52	78.8	0.59
Hispanic	2	6.1	8	12.1
Other	1	3.0	6	9.1
Education (years)
< 12	6	18.2	3	4.5	0.04
12	9	27.2	13	19.7
> 12	18	54.5	50	75.8
Preconception BMIb
<18.5	3	9.1	2	3.0	0.25
18.5-24.9	20	60.6	38	57.6
25.0-29.9	8	24.2	17	25.8
≥30.0	1	3.0	9	13.6
Cigarette smokingc
No	21	63.6	60	90.9	0.0009
Yes	12	36.1	6	9.1
Second hand smoke
No	25	75.8	59	89.3	0.07
Yes	8	24.2	7	10.6
Illicit drugs
No	28	84.8	59	89.3	0.51
Yes	5	15.2	7	10.6
First pregnancy
No	16	48.5	38	57.6	0.39
Yes	17	51.5	28	42.4
Gravidity
0	17	51.5	29	43.9	0.21
1	9	27.2	15	22.7
2	6	18.2	10	15.2
≥3	1	3.0	12	18.2
History of STId
No	28	84.8	65	98.5	0.015
Yes	5	15.2	1	1.5
Number of sexual partnerse
1	8	24.2	32	48.5	0.07
2	3	9.1	6	9.1
≥3	21	63.6	28	42.4
Same partner from previous pregnancy
No	10	62.5	5	13.5	0.0005
Yes	6	37.5	32	86.5

^aP values were calculated using Chi squared test or if cell size was <5 Fisher's exact test

^bBMI=body mass index in kg/m²

^cCigarette smoking one month before to one month after conception

^dSTI=sexually transmitted infection

^eOne case – did not report number of sexual partners