Doctors who care for these babies find mixed reaction in parents. "We see both ends of the spectrum," said Dr. Boyle. "We live in a culture in which people believe in miracles and want to save a life, but there are other parents who don't want to take major risks have a child with a disability. For most, this is a sudden emergency and tragedy that they have never thought about before."
Such was the case with Sara Vassallie, a 26-year-old middle school teacher, who credits her doctors at St. Louis Children's Hospital with saving the lives of her twins born last November at 25 weeks gestation.
Experiencing pre-eclampsia that threatened to shut down her liver, Vassallie underwent a Caesarian section to deliver Hanna and Halie — each barely over a pound. The girls spent two months on a ventilator, and little Halie nearly died from an infection.
"Hanna made a little noise like a squeak when she came out," said Vassallie. "Their skin was see-through."
The family's bill for the babies' first 30 days of care -- excluding the doctor's bills -- was more than $700,000. Since January, the girls have been home breathing on their own and breast feeding. Hanna, now four pounds, has made it to a crib, but Halie, only three pounds, is still sleeping in an isolette.
"The doctors were really good talking to us about what to expect," Vassallie said. "They gave us the best and worst scenarios. From the very beginning we decided to do whatever was necessary. But it's been an ongoing process. There have been a lot of ups and downs like a roller coaster."
All babies born prematurely are at risk, but in those born before 25 weeks about half will have significant neurological problems like blindness, deafness, seizure or cerebral palsy.
A few -- about 25 percent develop mild symptoms like attention problems, stiffness in their legs and mild learning problems. Only about three percent to five percent have good cognitive and other functions, according to Dr. F. Sessions Cole, professor of pediatrics at Washington University School of Medicine, a neo-natal research center.
"But we can't tell in the delivery room which baby is in the top one-quarter," said Dr. Cole, a neo-natalogist who has treated more than 1,000 babies in 17 years.
The key to a premature baby's survival lies in its ability to breathe. All four chambers of the heart are pumping at 16 weeks, but the fetal lungs are not able to cope until much later, according to Dr. Cole. Even when the lungs are mature, they need to be able to "remodel" to adapt to the outside world.
"The machines are better than they used to be," said Dr. Cole. But ventilators can induce scarring and injury. "There are other risks when organs are not ready to be in the outside world: blood vessels in the brain bleeding and the intestines are not prepared to ingest breast milk or formula and there is a risk of infection from outside germs."
"There is no point when a premature baby is out of the woods and there are multiple medical problems that restrict and make acutely difficult their long-term survival," said Dr. Cole. "All these factors improve the later the baby is delivered."