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The M.D.

Preterm birth rate doesn't make the grade

U.S. scores a D overall. More C-sections, IVF, older mothers may play a role.

December 01, 2008|Valerie Ulene | Ulene is a board-certified specialist in preventive medicine.

Last month, the U.S. received a set of grades from the March of Dimes, the nation's leading organization committed to preventing preterm births, that were nothing short of horrible.

The report card on premature births compared preterm birth rates with national objectives. Overall, the nation received a D. Not a single state merited an A, and only one, Vermont, earned a B. Eighteen states and Puerto Rico and Washington, D.C., received an F, and California squeaked by with a C.

Given recent trends, it's unlikely that these grades will improve any time soon. Rates of preterm birth in the U.S. have been steadily increasing for years. In 2000, 11.6% of infants were born prematurely. In 2005, the most recent year for which statistics are available, this figure had grown to 12.7%.

The consequences of premature birth can be serious. Premature infants are at greater risk of dying during their first year of life than full-term infants. They often suffer from breathing and feeding problems and are at risk for intracranial hemorrhage (bleeding in the brain) and potentially life-threatening gastrointestinal problems. Their immature immune systems leave them susceptible to serious infections such as pneumonia and meningitis.

There are long-term problems associated with prematurity as well, such as cerebral palsy and vision and hearing loss. Children born prematurely also frequently suffer from learning and behavioral difficulties.

Experts in maternal and fetal health are working to identify the underlying causes of this increase in premature births. It appears that a variety of factors are at play.

Births between 34 and 36 weeks of gestation, or the late-preterm period, have increased most dramatically (a full-term birth takes place at 40 weeks). Late-preterm births now constitute 72% of all preterm births, according to the federal Centers for Disease Control and Prevention.

The fact that women are having babies at an older age is thought to contribute to this increase. "When they do get pregnant, women who are well into their 30s are more likely to incur all of the problems associated with pregnancy -- including prematurity," says Dr. Alan Fleischman, medical director for the March of Dimes.

The use of in vitro fertilization and other types of assisted reproductive technology also plays a role. More than half of all pregnancies conceived with assisted reproductive technology result in multiple births, dramatically increasing the risk of prematurity. Roughly half of all twin pregnancies deliver before 37 weeks and only 1 in 10 triplet pregnancies progress to term.

Perhaps the most significant factor contributing to the rise in late-preterm births, however, is an escalation in the rates of cesarean delivery. About 1 in 3 infants in the U.S. is born by cesarean section. Though rates vary substantially among states, ranging from 21.6% in Utah to 36.8% in Louisiana, they are almost universally higher than those of most European countries. "There's been a change in the way we practice obstetrics," Fleischman says.

That change, ironically, is partly due to lifesaving technologies developed to save preterm infants, Fleischman says. These have made many obstetricians feel that they've succeeded if a woman doesn't deliver before 34 weeks and that babies are more or less out of the woods by that point in the pregnancy.

This belief has lowered doctors' trigger points for performing an elective induction and cesarean delivery before a fetus has reached full term. If a pregnant woman is experiencing minor difficulties (or sometimes if she is simply feeling uncomfortable), some doctors will deliver the baby prematurely thinking that it is better for the baby to be in the neonatal intensive care unit than the womb.

"The problem is, they haven't taken into account that even late-preterm infants often have bad outcomes," Fleischman says. These babies suffer some of the same immediate problems that more premature infants experience, and often struggle with subtle developmental problems later.

"Getting to term should be the goal," he adds. "We don't want to stop one medically needed early delivery. But many elective inductions and cesarean sections would benefit from more careful consideration."

A host of other factors including infections, genetics and poor prenatal care likely play a role in premature births that occur earlier than 34 weeks. Fleischman also suggests the importance of a less tangible factor -- stress. He believes that many kinds of stress including financial strains and abusive relationships put women at risk of delivering preterm.

He points out that in many developed countries where rates of prematurity are much lower, extensive social supports are extended to pregnant women.

"We talk a lot about being supportive of our women and children, but we don't behave in a way that is truly supportive," he says.

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