California has passed a controversial ban on same-sex marriage.

As the most widely reported of the 153 ballot measures at stake nationwide — California’s Proposition 8 calls for a constitutional amendment that would limit marriage to heterosexual couples. It is the first time such a vote has taken place in a state where gay unions are legal.

Sponsors of the ban declared victory early Wednesday, but the measure’s opponents said too many votes remained uncounted for the race to be called, AP reports. So the vote counting continued.

But just before noon Eastern time (9 a.m. in the West Coast), with more than 95% of the vote counted, the measure leads 52.1% to 47.9% opposed.

The LA Times reports on how the measure throws into doubt the unions of an estimated 18,000 same-sex couples who wed during the last 4 1/2 months.

Gay-marriage bans were also approved in Arizona and Florida, and gay rights forces suffered a loss in Arkansas, where voters approved a measure banning unmarried couples from serving as adoptive or foster parents. Supporters made it pretty clear that gay and lesbian couples were their main target.

In San Francisco, Proposition K, which essentially would have decriminalized prostitution, lost by 16 percentage points.

Meanwhile, voters in Colorado and South Dakota rejected measures that could have led to sweeping abortion bans, and Washington became only the second state — after Oregon — to offer terminally ill people the option of physician-assisted suicide.

Amendment 48 — the Personhood Amendment, a first-of-its-kind measure in Colorado, would have defined life as beginning at conception. Its opponents said the proposal could lead to the outlawing of some types of birth control as well as abortion.

Colorado for Equal Rights and other supporters of Amendment 48 said it would make Colorado the first state to guarantee the pre-born equal rights to life, liberty and due process of law. They said it would provide the legal foundation for ending abortion. But it lost by a three-to-one margin.

"We weren’t expecting that margin," Lauren Varner, spokeswoman for the "No on 48" campaign, told The Denver Post. "We’re excited we were able to reach and represent women all over the state of Colorado."