Premature twins were successfully delivered 12 days apart in a procedure so rare doctors at Humana Women's Hospital think it could be a first in North America, doctors said Thursday.

Doctors said the success of the deliveries could mean a better chance of survival for other premature twins.After her water burst during premature labor, Norma Landez gave birth Jan. 5 to son Aaron Jacob, who was more than two months early. The infant weighed a mere 2 pounds 6 ounces, and had to be placed immediately on a respirator.

But in a procedure so rare that no major medical journal had any report of its ever being done intentionally in North America, Landez's physician used surgery and medication to prevent for 12 days the birth of the second boy, Joshua David, who still was protected in the womb in an intact fluid-filled membrane despite the delivery of his twin brother.

The delay allowed the second baby to develop more fully before delivery.