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."