Table 1.

Characteristics and Perinatal Outcomes in 1.691 Million Primiparas (Para 1) Versus 2.510 Million Multiparas (Para 2+; the Reference Category), United States, 1990.

	Without controls				With controls Para 1 vs. para 2+ odds ratio
	Primipara para 1		Multipara para 2+
	Mean	SE	Mean	SE
Characteristics
Age	24.23	0.004	27.89	0.003
Parity	1.00	0.000	2.76	0.001
Birth weight, kg	3.31	0.000	3.37	0.000
Labor and delivery
CPD, %	6.68	0.020	1.68	0.009	4.74 (4.67, 4.81)
Dysfunctional labor, %	4.88	0.017	1.64	0.006	3.31 (3.27, 3.38)
Prolonged labor, %	1.95	0.011	0.46	0.004	4.67 (4.53, 4.80)
Primary C-section, %	23.79	0.033	6.98	0.016	5.36 (5.32, 5.41)
Critical C-section a , %	15.13	0.028	4.17	0.013	5.13 (5.08, 5.19)
Operative delivery, %	14.50	0.028	5.25	0.014	3.10 (3.07, 3.12)
Fetal distress, %	6.05	0.019	3.07	0.012	2.31 (2.29, 2.35)
Fetus and neonate
Male, %	51.37	0.038	51.11	0.032	1.01 (1.00, 1.03)
Low birth weight, %	7.18	0.020	6.78	0.016	1.32 (1.31, 1.34)
Preterm birth, %	10.27	0.023	10.84	0.020	1.08 (1.07, 1.09)
Birth weight <2.5 kg	4.32	0.016	4.21	0.013	1.20 (1.19, 1.22)
Birth weight ≥2.5 kg	5.92	0.018	6.58	0.016	0.96 (0.95, 0.97)
Infant deaths	8.24	0.070	9.23	0.061	1.05 (1.01, 1.08)
Neonatal deaths	5.69	0.058	5.54	0.047	1.39 (1.34, 1.44)
Postneonatal deaths	2.56	0.039	3.37	0.039	0.64 (0.61, 0.68)
Fetal deaths	10.25	0.077	18.80	0.086	0.84 (0.81, 0.87)
Infant and fetal deaths	18.41	0.102	24.01	0.075	0.97 (0.95, 0.99)

Raw means are tested for parity-related differences without controls (all significantly different, p < .001). Odds ratios with 95% confidence intervals are established via logistic regression, controlling for maternal age, tobacco use, education, marital status, prenatal visits, diabetes, and race/ethnicity. Deaths are per 1,000 births. CPD = cephalopelvic disproportion; C-section = cesarian section.

^a See the Methods section.