By Steven Reinberg
WEDNESDAY, June 24, 2015 (HealthDay News) -- Women who've had one stillbirth have a four times higher risk of having another stillbirth compared to women who've had a live birth, British researchers report.
The researchers noted that the overall risk of stillbirth is low. The review included millions of pregnant women, and fewer than 1 percent had a stillbirth. In a subsequent pregnancy, only 2.5 percent of women who'd experienced a previous stillbirth had another stillbirth, the study found.
"Despite the higher risk of recurrence, most pregnancies following a stillbirth will progress normally and end in the birth of a healthy baby," said lead researcher Dr. Sohinee Bhattacharya, a lecturer at the Institute of Applied Health Sciences at the University of Aberdeen in Scotland.
The researchers defined stillbirth as a fetal death at more than 20 weeks' gestation or a weight at time of death of at least 14 ounces (400 grams), according to the study. A death before 20 weeks is considered a miscarriage.
For the study, Bhattacharya and colleagues analyzed 16 studies that included almost 3.5 million pregnant women. All the women were from high-income countries, including Australia, Scotland, the United States, Denmark, Israel, the Netherlands, Norway and Sweden.
Among the women, 99.3 percent had a previous live birth and 0.7 percent had a stillbirth in an initial pregnancy. Stillbirths occurred in the subsequent pregnancy for 2.5 percent of women who had a previous stillbirth and in 0.4 percent of women with no history of stillbirth, the researchers found.
Twelve of the studies included in the review looked specifically at the risk of a stillbirth after a first one. Those studies revealed a four times increase in the risk of a second stillbirth, the researchers said.
What experts don't always know is why stillbirths occur -- whether it's a first or later pregnancy, Bhattacharya said.
"We know very little about these unexplained stillbirths even today," she said. "There are many systems that try to assign a cause of stillbirth, but with all of them, 10 percent to 40 percent remain unexplained."
The report was published June 24 in the BMJ.
Dr. Victor Rosenberg, director of the Center for Thrombophilia and Adverse Outcomes in Pregnancy at North Shore University Hospital in Manhasset, N.Y., said, "The first question a patient always asks me after experiencing a pregnancy loss is -- 'What are the chances of this happening again?' "
"The overall risk is still small, given that the baseline risk of stillbirth in the U.S. is only 6.2 per 1,000 pregnancies," said Rosenberg, who was not involved with the study.
Dr. Alexander Heazell, a senior clinical lecturer in obstetrics at the University of Manchester in England and author of an accompanying journal editorial, said that pregnancies after a stillbirth need to be carefully monitored.
"We would do scans to make sure the baby is growing normally and identify problems before they happen," he said. "The most common cause of stillbirth, the thing that doesn't work normally, is something that doesn't give the baby enough food and it wastes away," Heazell said.
Dr. Jennifer Wu, an obstetrician/gynecologist at Lenox Hill Hospital in New York City, said, "A stillbirth is a catastrophic event for a family."
More information is still needed on how best to improve outcomes, she said. "When a family experiences a stillbirth, recovering is a difficult and long process that is often greatly helped by a new healthy baby," Wu said.
Once a woman becomes pregnant again after a stillbirth, she should consult her midwife or doctor early, be aware of any signs that the baby is not growing or moving adequately and see her doctor or midwife if she's worried, Bhattacharya said.