DETROIT — Vance Terrell offered encouraging words to his pregnant sister during visits to a western Michigan hospital. It didn’t matter that she couldn’t see or hear him, and would never hold her twin sons.

Christine Bolden, 26, was already brain dead from aneurysms, but doctors kept her on a respirator for a month to allow for the development of babies who were born prematurely at 25 weeks. It was a rare procedure: In 2010, German researchers found just 30 similar cases worldwide dating back to 1982.

“It was hard to go up there and walk down the hallway and go into her room,” Terrell said Monday in a phone interview from Muskegon, Mich. “I knew she wouldn’t be talking to me. I’d rub her belly every time, and I’d rub her hands and kiss her and let her know I was there.”

Nicholas and Alexander Bolden weighed less than 2 pounds when they were born by cesarean section on April 5, and remain on ventilators at Helen DeVos Children’s Hospital in Grand Rapids.