1. Births: final data for 2008;Martin;Natl Vital Stat Rep,2010
2. Births: final data for 2009;Martin;Natl Vital Stat Rep,2011
3. Births: final data for 2010;Martin;Natl Vital Stat Rep,2012
4. Delayed childbearing: more women are having their first child later in life;Matthews;NCHS Data Brief,2009
5. Delayed childbearing by education level in the United States, 1969–1994;Heck;Matern Child Health J,1997