An analysis that used three age categories combined with marital status finds that the group with the highest share of births was married women ages 25-34, who were 37% of mothers of newborns in 2006. Unmarried women in the youngest age category (under 25) accounted for 23% of births. At the low end, only 2% of births were to unmarried women ages 35 and older — the so-called “Murphy Browns,” named for the TV character who became a single mother in 1992.