In 1989, the world's smallest known infant at the time, Madeline Mann, was born, weighing only 9.9 ounces, about six-tenths of a pound.
In 2004, another baby, Rumaisa Rahman, broke the record for smallest known infant at the time of birth, weighing only 9.2 ounces, just over a half-pound.
Thanks to progress in medical science, both babies have been able to grow normally, with normal speech and motor abilities and no chronic health problems, reported ABC News. Mann is now a 22-year-old college student and Rahman is a healthy first-grader.
Although both Mann and Rahman, who were born at the same hospital, have beat the odds, Dr. Jonathan Muraskas, the lead author of a study that looked at the development of premature babies with extremely low birth weight, says that their success seems to be the exception.
"The normal outcomes that are somewhat of a miracle," said Muraskas. "We don't want the public to look at these two and have false expectations about outcomes."
In addition to being "somewhat of a miracle," the babies benefited from prenatal care that involved their mothers receiving steroid injections before giving birth, in anticipation of a premature delivery. The steroids helped the babies' lungs and brains mature, reported The Los Angeles Times.
According to the March of Dimes, premature babies face an increased risk of mental retardation, learning and behavioral problems, cerebral palsy, lung problems, and vision and hearing loss. Studies also suggest that preemies are more susceptible to developing autism.
Medical expenses can also be extremely high, with the average preemie requiring $49,000 in medical expenses for his or her first year of life. In contrast, expenses for a baby born without complications costs $4,551.
These factors are what help determine the "viability" of a premature infant, with many doctors advising not to pursue neonatal care for an infant born under 23 weeks.
According to Time magazine, babies born under 23 weeks are only given "comfort care," which means the parents are able to hold them, but medical intervention is not used. If the parents insist on medical intervention, doctors abide, but the process can be difficult, with the baby sometimes being too small to even insert a breathing tube for resuscitation.
Nonetheless, high costs and grim statistics often matter very little to parents, who almost always opt for medical care to save the infant, Gerri Baer, a neonatologist in Rockville, Md., told Time.
"I can tell them what the stats are, but most people are going to believe their kid is going to be okay," she said. "If you're in that heightened emotional state, the data is not all that important to you."
Indeed, Dr. Muraskas warned that although his study of "miracle" babies focused on the success of their development, he hoped that it did not "propagate false expectations for families, caregivers and the medico-legal community alike."
Dr. Scott Berns, a senior vice president at the March of Dimes, also urged in a separate Time report that people should not lose sight of the big picture.
"It's incredibly wonderful how well these babies did," says Berns. "But we're still talking about a huge epidemic in this country where more than half a million babies are born each year preterm."
Although there are many factors that can lead to premature birth, including natural health problems, there are several things expectant mothers can do to help avoid delivering prematurely, such as getting prenatal care, according to the American Pregnancy Association.