A growing number of the smallest premature babies are surviving and, in many cases, thriving--but medical issues commonly persist long after birth. More from NBC News:
Alexis [Clarke] was born after she'd been in the womb just over 25 weeks; a typical pregnancy lasts 40 weeks. Babies born before 37 weeks are considered premature, but with medical and technological advances, it's no longer unusual for very preterm babies to survive. The key, in general, is a steroid for mothers and a drug for their babies.
Alexis' journey has been marked by ups and downs. Just as her parents thought she was ready to be discharged in time for Thanksgiving, one of her doctors told them she needed emergency eye surgery. Then a small cough raised concerns that she'd contracted whooping cough, prompting her to be put into isolation (tests came back clear). But an MRI of her brain delivered the good news that her development seems to be proceeding normally.
Baby Alexis is hardly the tiniest preemie born, but her journey from neonatal intensive care to home is typical of other extremely premature babies. In 2011, less than 1 percent of live births in the U.S. were considered "extremely preterm," delivered before 28 weeks. That represents more than 28,000 babies. Meanwhile, the total number of premature births in the U.S declined last year to 450,000, or 11.5 percent, the lowest preterm birth rate in 15 years.
"In the past six years we've had babies survive that we didn't think could survive," Dr. Krishelle Marc-Aurele, one of Alexis' doctors, told NBC San Diego.
Some hospitals are divided on treating babies born in the "gray zone," between 23 and 25 weeks. In the U.S, up to 90 percent of neonatal units resuscitate babies born as soon as 23 weeks. Younger than that and most doctors believe a baby is not viable. "The lower level of viability is inching down," said Dr. John Muraskas, who resuscitated the smallest surviving baby on record, Rumaisa Rahman, born in 2004 weighing 9.2 ounces.
Muraskas, a professor of pediatrics and neonatal/perinatal medicine at Loyola University Medical Center, said the key treatments began in the 1990s and have made all the difference.
Now doctors routinely give moms on the brink of delivering too soon two doses of steroids to help the baby or babies' lungs mature quicker and strengthen the blood vessels in the brain. That reduces the risk of a premature infant developing a brain bleed.
Once born, preemies receive surfactant, a drug administered through a breathing tube into their lungs that makes them stronger and less stiff, and able to breathe independently sooner.