The chance that an extremely premature infant in the United States will survive without major problems has greatly improved, but the odds are still against the very smallest and youngest, those born nearly four months too soon.
A study in the Journal of the American Medical Association looked at data from more than 34,600 babies born between 22 and 28 weeks of gestation. A normal pregnancy lasts about 40 weeks. Just a few more weeks in the womb before birth make all the difference. For preemies born at 27 weeks, survival without major problems climbed from 29% in 1993 to 47% in 2012.
The study found that the age of viability-being able to live outside the womb-has not changed much from 1993 to 2012. In 1993, 6% of babies in the study born at 22 weeks survived long enough to leave the hospital, compared to 9% in 2012. Of the 1,550 infants born at 22 weeks only 99 survived until at least hospital discharge, with 5 suffering no major complications.
The infants in the study were born at 26 academic medical centers in a National Institutes of Health research network. The babies weighed between 14 ounces to just over 3 pounds. Among the preemies born in 1993, 70% survived until hospital discharge, versus 79% in 2012; with higher rates for later births. The rate of survival without major complications increased by about 2% each year for babies born at 25 weeks to 28 weeks.
By 2012, more than half the oldest preemies who survived until hospital discharge had no major complications, which can include infection, brain bleeding, vision problems, severe intestinal disease, and lung problems.
Improvements in the survival of these infants are due to several factors, including more cesarean births, which may be safer for the tiniest infants; better infection control procedures; newer methods for helping preemies breathe without ventilators; and giving women steroids before childbirth to boost lung growth, according to the study.