Table 1. Sample characteristics by sex (column percents).

		Sex		Row N
		Girls (n=428)	Boys (n=446)
Maternal characteristics
Racial identity	White	62	64	543
	Black	26	26	226
	Other	12	10	95
Hispanic	Yes	12	8	86
Age, years	< 21	15	11	113
	21–35	65	69	586
	> 35	20	20	175
Education, years	≤ 12 (high school)	42	40	347
	> 12, < 16	25	22	198
	≥ 16 (≥ college)	33	38	304
Single marital status	Yes	41	39	348
Public insurance	Yes	38	32	301
Newborn characteristics
Gestational age, weeks	23–24	18	23	180
	25–26	46	45	396
	27	36	32	298
Birth weight, grams	≤ 750	40	34	323
	751–1000	43	44	379
	> 1000	17	22	172
Birth weight Z-score	< −2	8	4	51
	≥ −2, < −1	18	9	116
	≥ −1	74	87	707