Table 1.

Descriptive characteristics of mothers of infants who were or were not delivered preterm

	Percent of subjectsa				p Valueb
	<32 wk (n = 58)	32–34 wk (n = 120)	35–36 wk (n = 293)	≥37 wk (n = 5267)
Maternal race/ethnicity
Non-Hispanic white	46.6	52.5	57.3	59.6	<0.01
Non-Hispanic black	29.3	15.8	11.9	10.7
US-born Hispanic	8.6	11.7	12.6	10.2
Foreign-born Hispanic	10.3	10.8	9.9	12.5
Other	3.4	9.2	7.5	36.4
Education
<High school	19.0	15.0	17.4	16.8	0.47
=High school	31.0	31.7	25.9	24.5
>High school	48.3	53.3	55.6	58.2
Parity
0	46.6	41.7	40.3	39.8	0.76
1	36.2	30.8	29.7	33.4
2	10.3	16.7	18.4	17.4
>2	6.9	10.8	11.3	49.4
Vitamin/mineral supplement intakec
No	6.9	4.2	5.8	4.8	0.73
Yes	89.7	94.2	93.2	94.1
Smokingc
No	84.5	74.2	77.5	80.9	0.12
Yes	15.5	25.8	22.2	18.9
Alcohol intakec
No	75.9	62.5	66.2	59.5	0.01
Yes	24.1	36.7	33.4	40.0
Gestational diabetes
No	91.4	92.5	92.5	93.6	0.40
Yes	6.9	5.0	5.1	4.0
Fertility treatments or proceduresc
No	93.1	96.7	93.9	95.9	0.48
Yes	5.2	3.3	5.8	4.1
Maternal age at delivery (y), mean (SD)	26.21 (6.61)	27.23 (6.40)	27.74 (6.42)	27.55 (6.07)	0.33
Prepregnancy body mass index (kg/m2), mean (SD)	25.31 (5.53)	24.92 (6.82)	24.72 (5.58)	24.96 (5.66)	0.86

Abbreviation: SD, standard deviation.

^aPercentages may not equal 100 due to missing data or rounding.

^bFor categorical variables, chi-square tests were applied except for gestational diabetes. Fisher exact test was used for gestational diabetes due to 25% of the cells having expected counts less than 5. F test was used for continuous variables.

^cRefers to the period 1 month before through end of pregnancy.