Infant mortality has continued to drop in the U.S. during the past several decades. But stillbirths—when a fetus dies after 20 or more weeks of gestation—have remained relatively steady—and account for almost as many deaths as those of babies who die before their first birthday. About one in every 160 pregnancies in the U.S. ends in a stillbirth, which adds up to about 26,000 each year nationwide.

Two new studies, published online Tuesday in JAMA, The Journal of the American Medical Association, have analyzed data from large populations of still and healthy births in an effort to search for new causes—and to start to bring the mortality rate down.

Due to their emotional difficulty, stillbirths often go unexamined. Even for the health care provider, "it's really a very emotional event," says Jay Iams, a professor of maternal and fetal medicine at The Ohio State University Medical Center and author of an essay published in the same issue of JAMA. Previous studies of stillbirths had limited subject groups and generated smaller datasets. With the larger, population-based studies, the findings "should approximate better what we really expect to see in the U.S. population," remarks George Saade, chief of obstetrics and family medicine at the University of Texas Medical Branch at Galveston and co-author of one of the new studies.

What Saade's group and the authors of the second study found, Iams says, is "very powerful evidence" that the assumed risks behind—and the entire definition of—stillbirth should be reexamined.

Early risks

Compared with other developed countries, the U.S. has a relatively high rate of stillbirths. The new study by Robert Silver, a professor of obstetrics and gynecology at the University of Utah School of Medicine, and his colleagues helps to profile the most prevalent known causes of stillbirth. The researchers found that diabetes, smoking, drug addiction, being overweight, and being 40 or older all increased a woman’s chances of having a stillbirth.

Unmarried women who do not live with their partners were also more likely than married, cohabitating women to have a stillbirth, although that might be an indicator of larger socioeconomic factors, Saade notes.

The good news is that "many of these factors are modifiable," Saade remarks. So "women planning to get pregnant or women who might get pregnant should plan to be in the best possible condition before getting pregnant—and seek care early so that any of these factors [can] be identified," he says.

Troubling patterns

Not all risk factors can be modified, of course. And the stillbirth rate for black women is more than twice as high as it is for white women. This finding is not new, but with the new data, researchers have been able to dispel some of the previous assumptions about its causes. "The usual answer is it's access to health care, poverty and social risk," Iams says. But the data show that even after black women are in the hospital and are affluent and highly educated, they are still more likely to have a stillbirth. Why? Women of African descent living in the U.S. are nearly twice as likely as white women to give birth early, which increases the risk of complications and fetal death.

Previous research has shown that women who immigrate to the U.S. give birth at full gestation about as frequently as their white peers, but after two generations, their risk has increased. "Being raised in America is somehow associated with these adverse outcomes," Iams says. Whatever the causes, the disparity is "embarrassing," he concludes. But it is also "an opportunity because it explains some proportion of the premature births or stillbirths. It's a clue to figuring out what's happening."

Other immutable characteristics that seemed to increase a woman's odds of having a stillbirth included having an AB blood type and having had a miscarriage or stillbirth previously.

With these unmodifiable risks, "it's a balancing act" in knowing about them but keeping fear from taking over, Saade notes. The majority of women who have some of these unalterable risk factors will still have live births.

And one of the best way to develop a better understanding of the causes of stillbirths is to keep collecting data—which means evaluating new cases via placental analysis, autopsy and, when possible, genetic analysis. Despite the emotional challenge of evaluating stillbirths, it is "a very important thing" to do, Silver asserts. And often, the process can bring closure to families in addition to medical information that could help lessen the odds of future stillbirths for that mother—and others—he notes.

In need of new numbers

Even though the new studies shine a brighter light on the elusive causes of stillbirth, the reasons behind the majority of cases are still mysterious. "The biggest component to the risk for stillbirth is something else—some factors that we haven't analyzed yet or some factors we don't know," Saade says. In the stillbirths analyzed in Silver's study, more than a third had no probable cause.

Saade and his colleagues are still analyzing data collected from the two-year study and are going to be looking for genetic and genetic-environment trends. Newfound risk factors might help doctors assess a woman's risk of stillbirth early in pregnancy or even before she becomes pregnant. Ultimately, Saade hopes, "we'll have some kind of classification of risk" to keep a closer eye on women who might be more likely to lose their fetus some time after 20 weeks. "Then we can either modify the risk factor—or develop treatment that would prevent the stillbirth," he says.

One of the lasting challenges to addressing this problem might be that the very definition of stillbirths has been obscuring efforts to better understand it. "It's usually treated as something that's kind of separate," Iams says, rather than as part of a continuum of other pregnancy complications.

The assessment of stillbirths has, in large part, been controlled by how early a baby might be delivered and kept alive. Women between 24 and 32 weeks of gestation are watched closely for complications, Iams notes, because at that point a fetus can often survive as a preemie. But before 24 or 26 weeks, "we don't look at that as a time in pregnancy that you can deliver the baby and prevent stillbirth," he says.

Complications between 16 and 28 weeks of gestation have a lot in common and should be treated as such, rather than separating them into two distinct groups. "Without knowing what we're doing, we've chosen to draw a line in the middle of a group of people who have the same health issue," Iams says. "From the standpoint of the science, a woman who loses a baby at 19 weeks is the same as a woman who loses a baby at 22 weeks," he notes. ”The traditional 20-week boundary between 'miscarriage' and 'birth' is not clinically or scientifically useful and thus should be abandoned," he wrote in his JAMA essay.

But erasing the 20-week line is likely to be a battle. "It's a politically sensitive line that has a lot of history and advocacy around it," Iams says. Even many of his colleagues in the medical community have been skeptical of the suggestion—if only because they are used to it as a benchmark for patient assessment and their own data collection. He and others are starting to recognize the need for a recharacterization of the event itself, "but we're swimming upstream."

The new findings do not provide "the answer to how we're going to prevent it," Saade says of stillbirth. But "we're hoping that this is the start of that."