Table 1. Characteristics of the study sample, singleton births to US resident women age 15 to 44 years old from 1989 to 2013(n = 90,771,339 births).

Race/ethnicity			Total Frequency		% of total sample		% within maternal race/ethnic group
Maternal	Paternal
Non-Hispanic white (NHW)
	NHW		45,559,015		50.19		84.30
	NHB		1,113,311		1.23		2.06
	Hispanic		2,056,974		2.27		3.81
	Asian		390,507		0.43		0.72
	Missing		4,920,997		5.42		9.11
	All		54,040,804		59.54
Non-Hispanic black (NHB)
	NHW		303,238		0.33		2.22
	NHB		7,934,869		8.74		58.19
	Hispanic		195,816		0.22		1.44
	Asian		26,220		0.03		0.19
	Missing		5,175,807		5.70		37.96
	All		13,635,950		15.02
Hispanic
	NHW		1,727,674		1.90		9.24
	NHB		448,153		0.49		2.40
	Hispanic		13,937,222		15.35		74.5
	Asian		124,951		0.14		0.67
	Missing		2,469,375		2.72		1
	All		18,707,375		20.61
Asian
	NHW		698,565		0.77		15.92
	NHB		100,210		0.11		2.28
	Hispanic		145,153		0.16		3.31
	Asian		3,218,248		3.55		73.36
	Missing		225,034		0.25		5.13
	All		4,387,210		4.83
Parity
Nulliparous			37,135,151		40.91
Primaparous			29,284,946		32.26
Multiparous			24,351,242		26.83
Marital status
Married			59,621,905		65.68
Unmarried			31,149,434		34.32
Education attainment
0–8 years			5,133,797		5.66
9–11 years			14,121,856		15.56
HS grad/GED			28,462,106		31.36
Some college			21,049,080		23.19
College grad			13,980,080		15.40
More than college			8,024,420		8.84
Nativity
Native born			71,472,566		78.74
Foreign born			19,298,773		21.26
Age
< 20			9,994,192		11.01
20–29			48,366,027		53.28
30–39			30,522,619		33.63
≥ 40			1,888,501		2.08