A woman declared brain dead was kept on a respirator for a month until her twin boys could be born, a Michigan hospital said Monday.

Nicholas and Alexander Bolden weighed less than two pounds when they were born prematurely, at 25 weeks, by caesarean section on April 5. They remain on ventilators at a children's hospital in Grand Rapids, spokesman Bruce Rossman said.

It was a rare procedure: In 2010, German researchers found just 30 similar cases worldwide dating back to 1982.

"We certainly hope they make it, but at this time they're too young to make a confident prognosis," Rossman said. "Children born this early will be at high risk for chronic conditions. It's too soon to tell."

Christine Bolden, 26, of Muskegon, Mich., collapsed from brain aneurysms on March 1. She was declared brain dead five days later, but doctors kept her on a respirator until it was time to remove the boys, Rossman said.

Bolden's family asked doctors "to drop everything we could to save these babies. It wasn't that difficult a call," he said. "It required a lot of evaluations and discussions among our staff. They had to at least get to 24 weeks before we could consider delivery."

Ethical dilemma

Dr. Cosmas Vandeven, who specializes in high-risk pregnancies at the University of Michigan hospital, said Bolden's case is a "very exceptional scenario." An important ethical issue in cases like these, he said, is whether a brain-dead woman would suffer by being kept on a respirator and undergoing a C-section.

"Almost every parent would give their life for their child," Vandeven said. "But you need to get truly independent opinions: Are we sure we're not causing harm to the mom?"

He said 70 per cent of babies born at 25 weeks survive, but the risk for long-term health problems is high.