TUESDAY, Dec. 13, 2011 (HealthDay News) -- Stillbirth has long been a mysterious and devastating pregnancy complication. But two new studies are uncovering more about what causes stillbirth and the factors that may raise a woman's chances of having a stillbirth -- at least some of which are avoidable.
Stillbirth, defined as a fetus that dies during the 20th week of gestation or later, occurs in about one in 160 pregnancies in the United States, according to the American College of Obstetricians and Gynecologists.
In the first study, about 500 women who'd had a stillborn baby agreed to an autopsy and genetic testing of the fetus, an examination of the placenta, as well as interviews and an analysis of their medical record. The women were racially and geographically diverse, hailing from five states: Rhode Island, Massachusetts, Georgia, Texas and Utah.
Researchers were able to determine the cause of death in 61 percent of stillbirths, and a "possible or probable" cause of death in more than three-fourths of cases.
Placental abnormalities, such as blood clots, were blamed in 24 percent of stillbirths, making it the most common identifiable cause. Fetal genetic abnormalities, including trisomy 13 or 18 (involving an extra chromosome), and major birth defects of the brain or heart, were blamed in about 14 percent of stillbirths.
Infections, either bacterial or viral, were blamed in 13 percent of stillbirths. They included E. coli or group B strep, cytomegaloviris and parvovirus, which causes Fifth disease (a rash that can occur in childhood). While many women get those infections during pregnancy and their babies are fine, in a small number the infections can lead to stillbirth, said study author Dr. Robert Silver.
Umbilical cord abnormalities, such as blood clots, caused 10.4 percent of stillbirths, while hypertension in the mother was implicated in just over 9 percent of stillbirths. Other maternal medical conditions, such as diabetes, lupus and thyroid disease, were cited as contributing to about 8 percent of stillbirths.
Diabetes in the mother, especially, poses potential dangers for the fetus. "A poorly controlled diabetic is a very dangerous situation for the fetus, but if you have a well controlled diabetic, outcomes tend to be about the same as if you don't have diabetes," said Silver, a professor of obstetrics and gynecology at the University of Utah School of Medicine.
The study is published in the Dec. 14 issue of the Journal of the American Medical Association.
A second study in the same journal analyzed risk factors for stillbirth that can be identified before a woman becomes pregnant. Having a prior stillborn baby, having prior miscarriages and not having other children were all associated with added risk.
Women with diabetes had 2.5 times the risk of stillbirth and women aged 40 and older had 2.4 times the risk of stillbirth as women aged 20 to 34.
Having an AB blood type, smoking in the three months before pregnancy, overweight/obesity and a history of drug addiction were also associated with higher risks.
"Several lifestyle factors that are modifiable impact the risk of stillbirth," noted Dr. George Saade, a professor and chief of obstetrics and maternal fetal medicine at the University of Texas Medical Branch at Galveston. "Those include smoking, overweight/obesity and drug use. Women who are planning a pregnancy should look at all the modifiable factors they can improve on to be in the best condition possible when they start the pregnancy."
Black women are also at higher rate of stillbirth than white or Hispanic women, and the new research is starting to uncover some explanation for the disparities, noted Dr. Jay Iams, a professor of obstetrics and gynecology at Ohio State University Medical Center.
Black women are more likely to experience an "early stillbirth," or one before about 24 weeks, and are more likely to have a stillborn baby during labor (though not necessarily with a full-term baby).
"Are we simply not providing good care during labor to African-American women? I really don't think that's true," Iams said. "What's happening is that more African-American women are coming into the hospital in labor at 21, 22 or 23 weeks, and the babies don't have much of a chance to survive. The higher stillbirth rate is the result of a much higher rate of premature birth."
Each year in the United States, about 26,000 pregnancies end in stillbirth. Globally, there are 3 to 4 million, Silver said.
Despite major advances over the last 30 years in reducing the number of premature babies that survive, stillbirth rates have remained stubbornly high.
"It's a major public health problem, but people haven't put the same clinical or research energy into reducing stillbirth as they have infant death," Silver said. "When a baby is born prematurely, they do better than they did 20 years ago, but we haven't made the same advances in stillbirth."
Iams, who wrote an accompanying journal editorial, said it's about time that changed. Instead of considering stillbirth as a separate problem from premature birth, researchers and physicians are now better understanding that the causes of pregnancy loss starting at about 16 weeks -- such a problems with the placenta and umbilical cord -- are many of the same causes that also lead to babies being born prematurely and stillbirth.
That may include doing away with drawing the line for stillbirth at 20 weeks, Iams added.
"Stillbirth has been considered by itself, and because it's been considered separately, it hasn't been linked to more well-known conditions, such as premature birth," Iams said. "It's often treated as something that is not going to happen again, or a random event. What these researchers have shown is that if you look hard enough, more often than not, you can find a cause."
The March of Dimes has more about preventing premature births.