A study says doctors now have a better way of helping parents make an agonizing decision: When and if to take certain steps to save a very premature baby.

The number of weeks in the womb has generally been the chief factor. But the study shows others are important, too -- including whether the infant is a girl, and whether the child gets steroids for the lungs shortly before birth. Those factors can be just like an extra week of pregnancy.

A co-author of the study says the new information could change how doctors and parents decide what kind of care to provide to tiny, fragile premature infants. The research focused on extremely premature babies, those born after 22 to 25 weeks in the womb. A full term is about 40 weeks.

The study is published in the New England Journal of Medicine.