An anti-abortion group failed to get enough signatures to change the Ohio constitution to claim that life begins at fertilization.
Voters have rejected similar proposals that made ballots in 2008 and 2010 in Colorado. They also defeated the initiative last November in Mississippi, which has some of the nation's toughest abortion regulations.
Organizers say a personhood amendment has a good chance to qualify for the fall ballot again in Colorado. The state has a lower threshold of required signatures than Ohio; about 86,000 signatures are needed by early August.
The measures vary in some details, but in general they define human life as beginning with fertilization and are intended to ban virtually all abortions, even in cases of rape and incest. Many physicians have said the measures could make some birth control illegal and deter in vitro fertilization.