Table 2.

Adjusted odds ratios and 95% confidence intervals for medically induced preterm birth, from the National Center for Health Statistics Natality Files 2003^*

	Estimate (CI)
Prenatal Care (Reference Not Adequate)
Adequate	0.52 (0.51,0.53)
Superadequate	2.44 (2.40,2.49)
Missing	1.77 (1.70,1.84)
Maternal Race/Ethnicity (Reference White Non-Hispanic)
Black Non-Hispanic	1.44 (1.41,1.47)
Hispanic	1.16 (1.13,1.19)
Asian & Pacific Islander	1.09 (1.05,1.13)
Native American	1.20 (1.13,1.28)
Maternal Age in Years (Reference 25–29)
< 15	1.02 (0.88,1.18)
15–19	0.79 (0.77,0.81)
20–24	0.87 (0.85,0.89)
30–34	1.19 (1.17,1.21)
35–39	1.46 (1.43,1.50)
40–45	1.81 (1.74,1.88)
45–49	2.10 (1.86,2.35)
Pregnancy Plurality (%)(Reference Singleton)
Twin	9.31 (9.14,9.48)
Triplet+	38.5 (35.7,41.5)

^*Adjusted also for geographic division, marital status, maternal place of birth, education, gravidity, smoking and drinking during pregnancy, chronic hypertension, pregnancy associated hypertension, and eclampsia/pre-eclampsia