Effects of socioeconomic position and clinical risk factors on spontaneous and iatrogenic preterm birth

Table 2 Rates of preterm birth <37 weeks and preterm birth <32 weeks and crude and adjusted rate ratios by family income and contribution to a retirement saving plan (RSP) among singletons births, Nova Scotia, 1988 to 2003

Family income*/RSP	Preterm birth		Crude rate ratio	95% CI	P value	Adjusted rate ratio^‡	95% CI	P value
Family income*/RSP	Number^† Rate (%)^†		Crude rate ratio	95% CI	P value	Adjusted rate ratio^‡	95% CI	P value
Preterm birth <37 weeks
<$4,430	780	6.1	1.11	1.01-1.21	0.03	1.01	0.88-1.16	0.87
$4,430-$6,529	800	6.2	1.12	1.02-1.22	0.02	1.03	0.90-1.18	0.69
$6,530-$11,914	1,390	5.4	0.97	0.90-1.05	0.47	0.96	0.86-1.07	0.44
$11,915-$17,584	1,270	5.1	0.90	0.83-0.97	0.007	0.97	0.87-1.07	0.52
$17,585-$24,949	1,390	5.5	0.98	0.91-1.06	0.61	1.07	0.97-1.17	0.17
$ ≥ 29,450	1,380	5.6	1.00	-	-	1.00	-	-
RSP (no)	5,240	5.7	1.11	1.05-1.18	0.0001	1.08	1.00-1.16	0.06
RSP (yes)	1,780	5.1	1.00	-	-	1.00	-	-
Preterm birth <32 weeks
<$4,430	100	0.86	1.14	0.90-1.43	0.29	0.74	0.50-1.10	0.14
$4,430-$6,529	110	0.92	1.21	0.96-1.52	0.11	0.87	0.59-1.28	0.47
$6,530-$11,914	190	0.79	1.04	0.85-1.26	0.72	0.82	0.60-1.11	0.19
$11,915-$17,584	170	0.75	0.98	0.80-1.20	0.86	0.90	0.68-1.18	0.44
$17,585-$24,949	170	0.72	0.95	0.78-1.16	0.62	0.92	0.72-1.19	0.52
$ ≥ 29,450	150	0.76	1.00	-	-	1.00	-	-
RSP (no)	670	0.81	1.18	1.02-1.37	0.02	1.17	0.94-1.44	0.15
RSP (yes)	210	0.69	1.00	-	-	1.00	-	-

*Family income adjusted for family size and expressed in 1988 Canadian dollars.
^†All numbers rounded to the nearest 10 in tabular analyses, with crude rates (and crude rate ratios) obtained from logistic models (excluding those with a missing gestational age).
^‡Adjusted rate ratios were obtained from a logistic model that included maternal age, parity, marital status, residence, pre-pregnancy weight, smoking status, previous cesarean delivery, previous low birth weight, previous perinatal death and calendar period.

ISSN: 1471-2393