ALBUQUERQUE, N.M. -- The nation’s first citywide ballot initiative that would ban abortion after 20 weeks was trailing in early returns Tuesday night.

Among 50,000 early and absentee ballots,  about 56% opposed  the proposal and 44% supported it. There was no way to know whether those returns would be representative of the full turnout in New Mexico's largest city, however.

Polls closed in Albuquerque at 7 p.m., but news reports showed that people were still waiting in line to cast ballots. About an hour later, officials said nearly 37,000 people had voted on election day, bringing the total turnout to more than 87,000.  That's nearly a quarter of the city's approximately 360,000 registered voters.

The late-term abortion measure made Albuquerque the latest battlefield for the issue and a testing ground for whether abortion limits could be imposed on a local level.

The landmark 1973 U.S. Supreme Court decision that legalized abortion, Roe vs. Wade, has been interpreted to mean that abortions can be performed through 24 weeks of pregnancy. 

But states have attempted to chip away at the ruling. 

Earlier Tuesday, the Supreme Court refused to block a Texas law while opponents appeal. That law requires each clinic that performs abortions to have a doctor on staff with hospital privileges within 30 miles. Abortion rights advocates say that has forced one-third of the state's 36 abortion clinics from offering the procedure.

Albuquerque's "Pain Capable Unborn Child Protection Ordinance" needs a majority to pass. It would have statewide impact because the only late-term abortion providers in the largely rural state are in Albuquerque.

Women living out of state also fly to Albuquerque for the procedure.

The only exception to the ban would be for women whose lives would be in danger if they were to carry the fetus to term. There are no exceptions for rape or incest.

Roe vs. Wade held that a woman had a right to abortion until her fetus was viable, generally considered to be 24 weeks.

There doesn't seem to be a consensus on when a pregnancy is considered late-term, with definitions ranging from the 20th week of gestation to the 27th.

To get the measure on the ballot, antiabortion groups gathered 27,000 signatures — more than twice the number required. The ordinance could be implemented days after city officials certified the election.

Opponents of the measure, including state Atty. Gen. Gary King, have said they're prepared to sue if the measure passes.

Dave Sidhu, a constitutional scholar at the University of New Mexico, pointed to recent court rulings throughout the nation that have struck down similar bans at the state level.

In next-door Arizona, state officials have appealed to the Supreme Court after a 20-week limit on abortions was struck down by a federal court. Eleven other states have adopted similar limits. Several of these bans have been blocked by courts while litigation is pending.

 cindy.carcamo@latimes.com

@thecindycarcamo