Stlaske, 31, had given birth to two early-but-healthy sons, but their third, Tyler, was on the way nearly a month before his January due date. Doctors tried to stave off delivery but found Stlaske's amniotic fluid too low.

"They said they had to take him early," said Stlaske, a second-grade teacher from Crystal Lake, Ill. "It was terrifying."

Not long ago, Tyler's birth on Dec. 30 at 36 weeks' gestation would have been considered skirting the edge of prematurity, defined as being born before 37 weeks in the womb. Doctors would have treated him similarly to a full-term baby.

But after years of awareness education and clinical studies, medical professionals and parents increasingly consider so-called "late preterm" babies as distinct cases requiring specialized treatment. Hospitals have launched programs specifically targeting late preterm infants, those born between 34 and 36 weeks' gestation. And the efforts may be starting to yield improvements, experts say.

Though still statistically rare, health problems — such as respiratory difficulties, which Tyler developed — occur far more often in late preterm babies than they do in full-term infants.

In Illinois, the number of late preterm births increased about 18 percent between 1996 and 2006, to 9.3 percent of all live births, according to March of Dimes statistics.

But those numbers may be turning around. In 2007, the most recent year for which the March of Dimes has statistics, Illinois' numbers for late preterm births came in at 9.1 percent, a slight reduction.

"Doctors have this on their radar, very much so," said Dr. Faheem Uraizee, director of neonatology at Advocate Good Shepherd Hospital in Barrington, Ill., where Tyler was born. Late preterm birth "has been recognized as a very severe problem. Hopefully the spike that you have seen (in premature births) should stabilize."

Those hopes are partially pinned to the extensive efforts to draw attention to the issue by organizations such as the March of Dimes. The group has tried for years to increase awareness about the health effects associated with late preterm births, which can make up as much as 70 percent of all premature babies.

Dr. Diane Ashton, deputy medical director at the White Plains, N.Y.-based March of Dimes, said in the last three years researchers have begun to find more evidence that late preterm babies such as Tyler suffer higher risks of breathing problems, jaundice and increases in blood sugar levels. They're also more likely to be admitted to intensive care units and to be readmitted, according to experts.

At Central DuPage Hospital in Winfield, Ill., all infants at 35 weeks' or less gestation are admitted to neonatal intensive care, said the unit's medical director, Dr. Jeffrey Loughead. That wasn't the case until about 18 months ago. Before that, he said, the hospital made case-by-case calls on preemies and didn't necessarily focus more on late preterm infants.

Previously, he said, "if you were in your last several weeks ... people were pretty laissez faire."

Changes initiated over the last year and a half there, Loughead said, were in response to studies indicating that even a full-term baby of 38 weeks' gestation has double the mortality rate of a 40-week infant.

The hospital's new policies, which include more frequent monitoring of glucose levels and the temperatures of late preterm babies, have resulted in fewer readmissions, Loughead said.

"We don't have a long period of time to compare it to," he said, but "the preliminary data looks encouraging."

And when the choice on a delivery date is up to a mother and her doctor, experts now recommend waiting as long as possible. If an obstetrician counsels an antsy mom to hold off, said Loughead, "they're not being mean or arbitrary."

Dr. William MacKendrick, head of neonatology at Evanston Hospital, said plateaus in the numbers of late preterm births nationally are encouraging, but it will take time to see if the turnaround is permanent.

"It's probably a little early to tell," MacKendrick said, adding that he has seen increased awareness among medical professionals of the special problems late preterm babies can face.

Evanston Hospital sends all babies who spend fewer than 36 weeks in the womb to its infant special care unit, and anecdotal evidence shows the more frequent checks help, he said.

Part of the intensive monitoring comes from the fact that preemies' development can be unpredictable.

Proof positive of that is tiny Avery Luaces, swaddled in pink flannel in her parents' Grayslake, Ill., home.

David and Kathy Luaces expected a Valentine's Day baby. But in December, Kathy showed signs of preeclampsia, a condition marked by high blood pressure and high protein levels in urine after 20 weeks of pregnancy. If untreated, it can lead to serious complications including kidney and liver problems or even seizures. It can affect the birthing process.

Avery emerged via cesarean section at Advocate Good Shepherd on Jan. 1, weighing 4 pounds, 6 ounces, but was unusually healthy for being born so premature. Doctors pored over records of her respiratory development, a crucial milestone.

"She zipped right through that," said David Luaces, who also remembered requirements for temperature regulation and feeding. Her physicians told the couple Avery's hospital stay could stretch up to three weeks, but she was home in nine days.

While babies like Avery prove not all preemies suffer health problems, evidence exists that longer gestational periods lower the risk for some complications. In a study released in the New England Journal of Medicine in January 2009, researchers found increased likelihood of mortality, respiratory complications and admission to intensive care units in infants born by elective C-section at less than 39 weeks' gestation.

And in a December 2009 issue of the Pediatric Infectious Disease Journal, scientists said they'd found in late preterm infants higher rates of a serious bacterial infection called sepsis.

Scientists still aren't certain what causes premature births, but the March of Dimes said multifetal pregnancies, previous premature deliveries and cervical and uterine abnormalities are known risk factors.

The age of the mother, chronic health problems such as high blood pressure and obesity, and cigarette, drug and alcohol use during pregnancy also might contribute, the organization said.

The March of Dimes gave Illinois a D on its 2009 report card for preventing premature births, a grade that officials said was about average for the nation.

No state got better than a B on the rating, which is based on the percent of childbearing-age women who smoke (20 percent in Illinois), the percent who are uninsured (16.7 percent in 2009) and the rate of premature live births (about 13 percent in Illinois).

Dr. Dennis Crouse, a neonatologist and a professor of pediatrics at Southern Illinois University, said a woman's risk of delivering prematurely climbs after age 29, with statistics reaching 1 in 5 by the time she's 40.

"Women are delivering later in life," Crouse said, also noting that increasing numbers of fertility treatments contribute to the rise. But with national legislation on the horizon to limit the number of embryos that can legally be implanted in a woman, he said, some of those numbers may fall as well.

In Illinois, the state human services department funds community health centers' programs to educate parents on the importance of healthy pregnancies, efforts that officials hope will reduce premature births and infant mortality.