Pro-choice and pro-life activists demonstrate on the steps of the US Supreme Court on Monday in Washington, DC. In a 5-3 decision, the Supreme Court struck down one of the nation's toughest restrictions on abortion, a Texas law that women's groups said would have forced more than three-quarters of the state's clinics to close. Photo: CFP

The battle over abortion was expected to shift to measures focusing on the fetus in the wake of the US Supreme Court's decision striking down a Texas law enacted in the name of maternal health.

The 5-3 ruling held that Texas clinic regulations put an undue burden on women seeking abortion, a right established in the court's landmark 1973 Roe v. Wade decision.

The ruling could affect similar laws in more than a dozen states and stands as the biggest affirmation of abortion rights in more than two decades.

Opponents said they would regroup, turning their attention to defending and expanding laws that ban abortion after 20 weeks gestation or sooner.

But this path could be difficult as well. The Supreme Court has not taken up any outright ban on abortion tied to fetal gestation in decades and has repeatedly rejected pleas by states to endorse such laws.

"We believe that, even before today, these laws were very likely to be struck down because they are unconstitutional bans on abortion," said Emily J. Martin, general counsel for the National Women's Law Center. "Today's decision only strengthens that conclusion."

Abortion opponents acknowledged the defeat but vowed to press on.

"The pro-life movement takes two steps forward and, occasionally, a step backward," said Carol Tobias, president of the National Right to Life Committee. More than a dozen states now have provisions banning abortions after 20 weeks, "and we are going to be pushing that," Tobias said.

Nebraska enacted the first 20-week ban in 2010. Since then, similar laws have been adopted in Alabama, Arkansas, Georgia, Indiana, Kansas, Louisiana, Nebraska, North Dakota, Oklahoma, South Carolina, Texas, West Virginia, and Wisconsin, according to the Guttmacher Institute, a nonprofit research organization that supports abortion rights. Mississippi's law bans abortion after just 18 weeks.

Abortion opponents said they also planned to step up efforts encouraging states to limit second term abortions through bans on the use of dilation and extraction method. Nine of 10 abortions in the US are performed in the first trimester. But the dilation and extraction method is the most common procedure used for second trimester abortions.

Kansas and Oklahoma adopted bans on the procedure last year, but those laws have been blocked by courts. West Virginia, Mississippi, Alabama and Louisiana passed laws this year; none has yet to draw challenge.