Table 4. Correlation of preterm birth with age adjustment and clinical characteristics.

Clinical characteristic	Preterm birth without age adjustment				Preterm birth with age adjustment
	OR	95% CI	P value		OR	95% CI	P value
BMI	15.615	12.275–19.864	<0.001		16.717	13.533–20.650	<0.001
GA	1.722	0.795–1.423	0.678		1.077	0.803–1.445	0.621
Parity	2.061	0.999–4.251	0.049		1.735	1.496–2.011	<0.001
Labor	2.870	1.942–4.243	<0.001		2.434	2.403–2.899	<0.001
Sex	0.978	0.581–1.646	0.934		0.997	0.623–1.596	0.991
IBW	1.061	0.685–1.644	0.790		1.001	0.670–1.495	0.996
pPROM	2.227	1.615–3.071	<0.001*		2.266	1.641–3.130	<0.001

*, P value <0.05. BMI, body mass index; GA, gestational age; IBW, birth weight; parity, nulliparous or multiparous; labor, vaginal birth or cesarean birth; pPROM, preterm premature rupture of (fetal) membrane <37 weeks; OR, odds ratio; CI, confidence interval.