Last week, four month old Amillia Sonja Taylor went to a place she’s never been before and one it wasn’t certain she would ever see: her home in South Florida.

Amillia’s story as one of the world’s smallest, prematurely born babies ever to survive has put a spotlight on the incidence of premature births in the United States. Despite the exemplary pre-natal medical care available to expectant mothers in the U.S., pre-term birth rates in this country are on the rise.

What made tiny Amillia’s case extraordinary is that she was born before 22 gestation. Generally, babies born at less than 25 weeks do not survive. Full-term births are defined as those after 37 to 40 weeks in the womb. The National Center for Health Statistics reports that about 12.5 percent of babies born in the U.S. are born prematurely each year, and this percentage has risen nearly 30 percent between 1981 and 2004. The March of Dimes reports that preterm births are the second leading cause of infant mortality in the U.S. after birth defects.

However, doctors acknowledge that the developmental impact of premature births on babies is relative to the gestation period.

(Story continues below)

Dr. Milton Hutson, a specialist in maternal fetal medicine in New York City, says that while the overall premature birth percentage seems high and alarming, in fact only 2 percent of the premature births in the U.S. are under 32 weeks. Babies born under 32 weeks are at the highest risk for developmental problems such as cerebral palsy, neurological damage, chronic lung disease, blindness and hearing loss.

“Late term preemies, meaning those born between 34 and 37 weeks, usually do very well,” said Hutson.

The reasons for the rising rates of preterm births remains a source of medical debate. Amillia was conceived through in vitro fertilization, and there is a perception that the increasing use of fertility techniques like IVF-- which has increased the number of multiple births, thereby increasing the number of preterm births--is to blame. But while it is typical for multiples to be born prematurely--it is very common, Dr. Hutson said, for triplets to be born at 36 weeks-- Dr. Hutson believes that the number of multiples (whether conceived via IVF or naturally) is such a small number that these births would not have such a dramatic impact on the number of premature babies born annually.

The March of Dimes’ deputy medical director, Dr. Diane Ashton, cites a laundry list of identifiable risk factors that contribute to premature birth : obesity, diabetes, high blood pressure, maternal age (under 17 or older than 35), and a previous history of premature birth. Amilla's birth was triggered by an infection her mother contracted during pregnancy--another common risk factor for premature birth.

“But in 50 percent of the cases, we don’t know why [the baby was born prematurely],” Dr. Ashton said.

Advanced technology within neonatal intensive care units (NICUs) have increased the viability of all preemies, but less progress has been made in preventing or controlling preterm labor. To date, those efforts have been targeted at specific issues--such as helping women with a history of delivering prematurely--explained Dr. Richard Polin, director of the Neonatal Intensive Care unit at Morgan Stanley Children’s Hospital of NewYork Presybterian Hospital.

For women with a history of preterm birth, medications such as high-dose progesterone (17P) have been used to stave off labor. Research released in early February by the Society for Maternal-Fetal Medicine suggests that this progesterone may be used for women during their first pregnancy.

Restricted activity or bed rest may be imposed, just as it was before actress Marcia Cross, star of the hit ABC show Desperate Housewives, gave birth to her twins recently. Another preventive measure is stitching closed a woman's cervix in order to hold the baby in the womb.

As for Amillia and other early preemies, Dr. Polin believes that it will be a while before her family learns whether her very-early delivery has affected her development.

“By two to three years, pediatricians get an impression, and by five to six years whatever consequences will be evident,” Dr. Polin said.

FOXnews.com Health writer Angela Macropoulos contributed to this report.

For more great information on living healthy through every decade of life, click here to check out Dr. Manny's book The Check List (Harper Collins, 2007).

Dr. Manny Alvarez is the managing editor of health news at FOXNews.com, and is a regular medical contributor on the FOX News Channel. He is chairman of the Department of Obstetrics and Gynecology and Reproductive Science at Hackensack University Medical Center in New Jersey. Additionally, Alvarez is Adjunct Professor of Obstetrics and Gynecology at New York University School of Medicine in New York City.