Table 5.

Adjusted ^a odds ratios and 95% confidence intervals of the association of relative household income with preterm birth, stratified by % of Black residents in census block groups, among 5,182 participants, Black Women’s Health Study, 1995–2003

	< 14.4% Black residents (n= 1,299)				14.4 – 82.7% Black residents (n= 2,592)				> 82.7% Black residents (n= 1,291)
Relative household income	No. term	No. preterm	Odds ratio	95% confidence interval	No. term	No. preterm	Odds ratio	95% confidence interval	No. Term	No. preterm	Odds ratio	95% confidence interval	p valueb
All preterm birth
Higher income	634	104	0.71	0.50, 1.00	1446	237	1.04	0.78, 1.37	706	136	1.80	1.14, 2.82	0.002
Similar income c	292	68	1.00	Referent	474	78	1.00	Referent	228	27	1.00	Referent
Lower income	171	30	0.80	0.48, 1.32	295	62	1.21	0.83, 1.76	162	32	1.61	0.92, 2.82	0.03
Spontaneous preterm birth
Higher income	634	53	0.69	0.43, 1.09	1446	124	1.02	0.70, 1.48	706	74	1.96	1.07, 3.59	0.01
Similar income	292	35	1.00	Referent	474	41	1.00	Referent	228	14	1.00	Referent
Lower income	171	14	0.67	0.34, 1.34	295	28	1.09	0.65, 1.82	162	19	1.87	0.90, 3.89	0.03
Medically indicated preterm birth
Higher income	634	51	0.74	0.46, 1.18	1446	113	1.05	0.71, 1.55	706	62	1.62	0.86, 3.05	0.04
Similar income	292	33	1.00	Referent	474	37	1.00	Referent	228	13	1.00	Referent
Lower income	171	16	0.98	0.50, 1.93	295	34	1.32	0.80, 2.19	162	13	1.35	0.60, 3.04	0.24

^aAdjusted for age, education, marital status, body mass index, and smoked cigarettes during pregnancy.

^bp value for interaction term between higher or lower relative household income and % Black residents (ordinal).

^cSimilar income is defined as no difference in category of household income for the participant with that of her block group.