Two of the tiniest preemies that doctors have resuscitated are a success story — though many more are a cautionary tale, finds a new study. 

Their combined weight a mere 540 grams, both babies, Madeline Mann, born in 1989 weighing 9.9 ounces and seven-year-old Rumaisa Rahman, whose 9.2-ounce birth weight remains the world's tiniest, are thriving. Mann is now an honours student majoring in psychology, while Rahman is a healthy first grader, according to the report. 

Their stories are documented in the online Monday issue of the journal Pediatrics.

But these two are the exceptions, and their remarkable health years later should not raise false hope, say the study's authors: Most babies this small do poorly and many do not survive even with advanced medical care. "These are such extreme cases," said Dr. Jonathan Muraskas of Loyola University Medical Center. They should not be considered "a benchmark" to mean that doctors should try to save all babies so small, he said.   

The report addresses a question that was hotly debated when Mann was born 22 years ago, remains hot now — and still has no answer: "What is the real age of viability? No one knows," said Dr. Stephen Welty, neonatology chief at Baylor College of Medicine and Texas Children's Hospital in Houston.   

Muraskas and the report's co-authors say most newborn specialists consider babies born after 25 weeks of pregnancy to be viable — likely to survive — and so they should receive medical intervention if necessary to breathe. Younger babies are generally in a "grey zone," where intervention isn't always so clear cut, the report suggests.   

In Japan, doctors have lowered that threshold — the gestational age — to 22 weeks. Normal pregnancies last about 40 weeks. Some U.S. doctors will attempt to save babies at 22 weeks, but that is not done routinely, said Dr. Edward Bell, a University of Iowa pediatrics professor. Bell estimates that about 7,500 U.S. babies are born each year weighing less than 1 pound, and that about 10 per cent survive.   

Sometimes tiny babies with zero chance of surviving show signs of life at birth, and may be able to breathe for a short time if put in an incubator and hooked up to a breathing machine and intravenous treatments. "But even so, if it's a baby that doesn't have a chance, we don't want to put the baby and the family through the discomfort," Bell said.   

Gestational age more critical than size

Muraskas says his report highlights a sometimes overlooked fact: gestational age is even more critical for survival than size.  Rumaisa and Madeline were both palm-sized, weighing less than a can of soda — the average size of an 18-week-old fetus but they were several weeks older than that. Their gestational ages — almost 26 weeks for Rumaisa and almost 27 weeks for Madeline — meant their lungs and other organs were mature enough to make survival possible.    

Before the births, both mothers were given steroid drugs to speed up growth of the babies' immature lungs. Even so, Rumaisa and Madeline were on breathing machines for about two months, and hospitalized for about four months.    Madeline had mild brain bleeding, common in tiny preemies, but with no lasting effects. She and Rumaisa got treatment for an eye condition common in preemies called retinopathy, which in severe cases can cause blindness.   

For the Mann family, Madeline's survival is a source of pride and wonder. "I don't know why, we were just extraordinarily lucky," her father says.