TABLE 2.

Prediction of Chronologic Age at First Pregnancy Among Adolescent Girls: Colorado Adolescent Maternity Program, 1991–2005

Group	B	Adjusted R2	R2 Changea	F	F Changea	P
All (N = 1030)
Step 1: Menarche, y	0.2	4.4		48.1		<.001
Step 2
Menarche, y	0.5	26.7	22.3	188.0	139.9	<.001
Gynecologic age at coitarche, y	0.5
White (n = 323)
Step 1: Menarche, y	0.2	5.5		19.7		<.001
Step 2
Menarche, y	0.1	24.0	18.5	51.7	32.0	<.001
Chronologic age at coitarche, y	0.4
Hispanic (n = 399)
Step 1: Menarche, y	0.2	2.4		10.7		<.001
Step 2
Menarche, y	0.5	30.1	27.7	86.6	75.9	<.001
Gynecologic age at coitarche, y	0.5
Black (n = 308)
Step 1: Menarche, y		5.4		18.4		<.001
Step 2	0.2
Menarche, y	0.5	27.4	22.0	58.9	40.5	<.001
Gynecologic age at coitarche, y	0.5

Note. Gynecologic age was defined as age at coitarche minus age at menarche. Step 1 of the hierarchical regression models included, chronologic age at menarche; step 2 included gynecologic age at coitarche, chronologic age at coitarche, and prepregnant body mass index.

^a“Change” indicates improvement in R² or F when the second predictor is added.