Each year, a growing percentage of America's babies are born too soon, before they're physically ready to come into the world.
More of these infants are surviving than ever before - at least 500,000 in 2004. But the survivors face increased risks of cerebral palsy, mental retardation, vision problems, hearing deficits, and other developmental and learning issues.
The economic consequences are staggering - at least $26.2 billion a year, according to a "conservative" estimate yesterday from a panel of experts assembled by the National Academies' Institute of Medicine.
"And yet preterm births have not received the attention and funding necessary to fully understand the causes and consequences and to reduce the numbers," said Dr. Richard E. Behrman, who chaired the committee.
In 2005, preterm births totaled 12.5 percent of all births, a 30 percent increase from 1981. Although black mothers are still more likely to deliver preterm babies, whites, Hispanics and Asians are all seeing increases, regardless of income or education.
Among the possible causes: an increase in in-vitro fertilization, higher birth rates among older women, and a greater willingness by doctors and mothers to deliberately deliver babies before their normal 40-week term.
"It's very clear that preterm delivery is not just one disease; it's a very complex phenomenon that results from multiple interactions between genes and the environment," said Dr. Marilee C. Allen, a neurodevelopmental pediatrician and professor at the Johns Hopkins University School of Medicine who served on the study panel.
"The only way to attack the problem is to come at it from many points of view. ... It's not going to be a magic bullet," she said.
The committee called for sustained federal funding of research into the causes and prevention of preterm births, along with integrated research centers to tackle the scientific mysteries, track the consequences and find solutions.
The committee defined "preterm births" as any that occur more than three weeks early - before a pregnancy's 37th week. In recent years, scientists have adopted gestation length to replace birth weight as the best indicator of preterm birth.
Researchers say preterm births are the single greatest cause of poor outcomes in pregnancy. Half of all cases of cerebral palsy, a quarter of mental retardation, a quarter of hearing loss and a third of vision impairment in children are found among preterm babies, according to Norman J. Waitzman, an economist at the University of Utah, Salt Lake City and member of the study panel.
Even minor prematurity - a week or two - carries small but measureable degrees of added risk. The medical costs of these "late" preterm infants average 30 percent higher than those of full-term babies, the panel said.
In 2005, the committee estimated, a preterm baby's medical care, added to maternal care, early intervention, special-education services, lost household and labor productivity alone averaged $51,600 per child.
"It absolutely is a floor in terms of an estimate," Waitzman said. It does not consider many costs that extend beyond age 5 or other lifetime consequences for disabilities.
"It's clear that many parents are not prepared, not aware of some of the profound implications of this birth," Waitzman added.
Dr. Jay D. Iams, a panel member and vice chairman of obstetrics and gynecology at Ohio State University, said "miracle baby" stories have convinced most Americans that even very tiny preterm infants will survive and thrive.
"That translates into, 'It's no big deal to have my baby born early,'" Iams said. "But it is a big deal, and it's a much bigger deal than people realize ... and that's a reason it has not received the kind of research support it deserves."
One mystery is why black women have much higher rates of preterm births than other women.
In 2003, the committee reported, 17.8 percent of births to black women were preterm, compared with 11.5 percent among whites, 11.9 percent among Hispanics and 10.5 percent among Asians.
Such medical disparities are often traced to African-Americans' lower average income and limited access to care. But the difference in preterm births persists even when researchers control for those factors, Iams said.
Scientists say new funding could help them investigate one recent theory: that stress may be a factor.
"It has to do not so much with the acute stress of a single event," Iams said, "but perhaps the chronic stress of being an African-American woman throughout your life and the effect on how your body responds ... and ultimately triggers preterm birth."
But the trend lines - all upward - are a problem for all groups. The causes are likely as numerous and varied as they are unclear.
"Our modern life, with all its stress, may certainly have an impact," said Allen, the Hopkins pediatrician. "It may also be environmental toxins we're not aware of that affect whatever makes a mother begin the delivery process sooner than she should."
Infection is another possible contributor, she said. "We need to evaluate that very carefully."
Adolescents younger than 16 are twice as likely to have a preterm birth as those 18 and older. Women over 35 also have increased risk.
Another strong risk factor is a prior preterm delivery, which doubles a woman's normal risk of having a baby early, the report states. A woman who was born prematurely is also more likely to deliver too soon.
Multiple births also come with sharply increased risks of preterm delivery. "Having more than one baby in the uterus incurs a several-fold increased risk for preterm birth," Iams said. "It approaches 40 percent for twins and gets closer to 70 or 80 percent for triplets and beyond."
That has raised questions about in-vitro fertilization technologies that implant multiple embryos in the hope that at least one will survive. Often, several do.
Behrman said U.S. medical societies are reviewing standards of practice here now that doctors in Europe and elsewhere are moving toward single-embryo transplants that avoid high-risk multiple pregnancies.
Other contributing factors, the committee said, may include a greater willingness to induce labor in a "medically chosen" preterm birth. These occur when doctors and families decide that other concerns about the health of the fetus outweigh the benefits of keeping the baby in the womb longer.
"I think that explains some of the increase," Iams said. But the science is still unclear, he added, and more research is needed.
Meanwhile, panel members said they hoped their report would increase the public's awareness and readiness to respond.
"Preterm birth is always a surprise in a first pregnancy," Iams said. "It's very difficult for women to know when to call their doctors." And too often they're told not to worry.
"Persistent discomfort of any sort in the abdominal or pelvic area - regardless of whether you have a tremendous amount of pain - should be evaluated, and you shouldn't feel shy about contacting the health care system," Iams said.