August has the highest percentage of births

August had the most births each year from 1990 to 2006 except for six years (1992, 1993, 1997, 1998, 2003 and 2004) when it was edged out by July, according to National Center for Health Statistics. Historically, the sweltering, late-summer months are when obstetricians witness an increase in the arrival of newborns.