Table 1.

Summary statistics for the study sample and the overall United States

New Jersey 1997–2006; New York City 1994–2004; Pennsylvania 2004–2010: >1 birth per motherUnited States 1989–2008: All births
Birth outcomes
 Gestation length (wk)38.7992.02038.9200.190
 Birth weight (g)3,3355653,33825
Mother characteristics
 >12 y of education0.4940.5000.4490.042
 Pregnancy weight gain (lb)30.013.730.50.4
 Prepregnancy weight (lb)147.136.0
Number of births1,435,21378,176,946
Number of mothers647,050
  • Sample restrictions: single births with nonmissing information on gestation length. Prepregnancy weight and mother identifiers are not available in the US-wide data.