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.
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.
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."