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About 26,000 women in the United States give birth to a stillborn child each year. It's a harrowing experience for parents, and many eventually want to know what went wrong, in part to avoid going through a similar experience in the future. But in the days after delivery, when tests to search for a cause must be conducted, doctors are often hesitant to suggest them, and grief-stricken parents often reluctant to permit them.

A rigorous new study found that two tests are particularly effective in determining the cause of a stillbirth, a death of a fetus at or after 20 weeks of gestation. An examination of the placenta helped find a cause in about two-thirds of stillbirths, and a fetal autopsy helped in roughly 40 percent of cases, researchers reported. Genetic testing was the third most useful test, helping to pinpoint a cause 12 percent of the time.

"These tests have an impact, and now there's more of a scientific rationale for their use," said Dr. Emily Miller, an assistant professor of obstetrics and gynecology at Northwestern University who was not involved with the study.

She predicted that this critical new data would not only persuade more obstetrician-gynecologists that placental testing "is something we really need to recommend," but also help convince bereaved parents that follow-up testing is "worthwhile." In some cases, knowing the cause of a stillbirth can help to guide management of subsequent pregnancies.

The American College of Obstetricians and Gynecologists has long recommended a slew of possible tests after stillbirths, but this study, published in the journal Obstetrics and Gynecology, is the first nationwide attempt to calculate the relative utility of each. Researchers analyzed 512 stillbirths from 2006-08 from 59 hospitals in five states: Utah, Rhode Island, Massachusetts, Georgia and Texas. The cases are part of second analysis of a study by the Stillbirth Collaborative Research Network, a group funded by the National Institutes of Health that aims to improve stillbirth reporting and to pinpoint its causes.

That network of researchers had previously determined that complications during the birth process, including preterm labor and premature rupture of the amniotic sac, accounted for 30 percent of stillbirths. Before labor, placental problems were the most common cause of stillbirth, accounting for roughly one-quarter of cases. Genetic conditions or birth defects were responsible for about 14 percent of stillbirths, infection for 13 percent and umbilical cord issues another 10 percent.

Researchers defined whether a test was useful if it helped establish a probable or possible cause, or if it ruled out a possible cause.

A detailed evaluation of the placenta is not always done after stillbirth because a perinatal pathologist is not available or a physician may not send it for analysis, experts said. And prior studies have estimated that fewer than half of stillbirths are evaluated by autopsy.

Some of that reflects parents' reluctance. "People are angry, upset, and they feel like it won't make a difference," said Dr. Robert Silver, interim chairman of obstetrics and gynecology at the University of Utah Health Sciences Center and the study's senior author. Some parents have cultural objections to autopsy, or think it's God's will that they suffer a loss, or they worry unnecessarily that the body won't be back for burial in a timely fashion, he said.

Physicians, meanwhile, also often struggle to have that difficult bedside conversation with grieving parents. "It's uncomfortable," said Silver. "Doctors just want to run away," he said, but "it's worth working through any reservation they may have."