Smallest preemies more likely to survive without complications

Survival rates for the earliest premature babies are improving, with fewer of these very small newborns suffering serious complications, according to a study released Tuesday.

Prematurity still carries enormous risks, especially for babies as small as those in this study, who were born between the 22nd and 28th week of pregnancy. A typical pregnancy lasts about 40 weeks.

Only 9% of babies born at 22 weeks survived in 2012, for example, up from 6% in 1993, according to the study, which included 34,636 infants who had birth weights ranging from 14.1 ounces to 3.3 lbs. Among babies born at 28 weeks, survival improved from 91% in 1993 to 94% in 2012.

The biggest jumps in survival were in babies born at 24 and 25 weeks. Among those born at 24 weeks, survival increased from 52% to 65%; among those born at 25 weeks, survival rose from 58% to 81%, according to the study, funded by the National Institutes of Health.

Complications — such as blindness, a life-threatening intestinal inflammation or bleeding inside the skull — are also more common among the earliest preemies. None of the babies born at 22 weeks survived without major complications, in any year.

But among those born at 28 weeks, survival without complications rose from 38% to 56%, the study said.

Two decades ago, few babies born at 22 to 24 weeks survived at all, said Jeffrey Kaiser, a professor of pediatrics and obstetrics and gynecology at Baylor College of Medicine in Houston. He called the new study "fabulous news."

"It goes to show that persistence and continuing to do research and continuing to put money into all of this has really led to improvements," said Kaiser, who wasn't involved in the new study.

Prematurity is a major driver of the USA's high infant mortality rate.

The USA's premature birth rate rose for three decades, peaking in 2006 at 12.8% of all newborns before falling to 11.4% in 2013. About two-thirds of babies who die in the first year of life are born prematurely, according to the Centers for Disease Control and Prevention.

The USA ranks last among 26 high-income countries in terms of infant survival, according to the Organisation for Economic Co-operation and Development, below even former Eastern Bloc countries such as Hungary and Poland.

In a statement, Rosemary Higgins, a neonatal researcher at NIH, credited babies' improved survival to changes in medical practice. For example, women who go into early labor are now given corticosteroids to help mature the fetus' lungs and prevent respiratory distress.

In 1993, doctors gave steroids to only 24% of women at risk of delivering prematurely. By 2012, doctors gave steroids to nearly 87% of at-risk pregnant women, the study said.