. Author manuscript; available in PMC: 2016 Jan 31.

Published in final edited form as: Arch Gynecol Obstet. 2014 Nov 4;291(2):287–298. doi: 10.1007/s00404-014-3521-0

Table 2.

Relationship of pregnancy characteristics and design variables with birth outcomes for 372 infants, National Longitudinal Study of Adolescent Health, Wave IV, 2008.

	Proportion or Mean (SE)	Birthweight, grams m = 3398.8 (SE = 43.5)	Gestational age, weeks m = 39.18 (SE = 0.16)

		Estimate, 95% CI	Estimate, 95% CI

Infant sex
Boy	54.5%	(ref)	(ref)
Girl	45.4%	−163.3 (−359.6, 33.1)	0.34 (−0.38, 1.03)
Initiation of prenatal care
First trimester	51.9%	(ref)	(ref)
Second or third trimester	48.1%	−96.6 (−290.3, 97.1)	−0.49 (−1.38, 0.40)
Parity
Primiparous	87.0%	(ref)	(ref)
Multiparous	13.0%	50.3 (−83.3, 183.8)	−0.40 (−1.04, 0.23)
Months between interview and conception	18.8 (1.5)	3.0 (−3.8, 9.8)	−0.02 (−0.05, 0.01)
Relationship type
Dating	28.9%	(ref)	(ref)
Cohabitating	26.6%	40.2 (−218.9, 299.3)	0.87 (−0.27, 2.00)
Married	44.6%	229.2 (−25.8, 484.1)	0.53 (−0.47, 1.52)

Note. Proportions and means are weighted. Linear regression models control for maternal and paternal demographic factors: age at birth, race, education, receipt of welfare, and immigration status. SE = standard error; CI = confidence interval.