Table 5. Obstetric history, family history and risk of preterm birth.

	Preterm group		Control group		P	OR	95%CI
	n	%	n	%
Inter-pregnancy intervals
≤6 months	65	10.7	78	11.7		1.000
7–12 months	134	22.1	136	20.3	0.605	1.184	0.624–2.248
13–24 months	137	22.6	157	23.5	0.459	1.256	0.687–2.296
>24 months	269	44.5	298	44.5	0.134	1.564	0.871–2.809
History of preterm birth
No	1362	97.9	1388	99.8		1.000
Yes	29	2.1	3	0.2	0.000	9.667	2.945–31.732
Reproductive abnormality
No	1355	98.3	1372	99.6		1.000
Yes	23	1.7	6	0.4	0.003	3.333	1.561–9.414
Family genetic diseases
No	1384	99.6	1385	99.9		1.000
Yes	6	0.4	2	0.1	0.178	3.000	0.606–14.864