Most Common Causes, Risk Factors for Stillbirth

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The Stillbirth Collaborative Research Network (SCRN) has reported that performing a systematic medical evaluation leads to a probable or possible cause of death in the majority of stillbirths. According to a study published in the Dec. 14, 2011 issue of the Journal of the American Medical Association (JAMA), the most common causes of stillbirth differ across racial and ethnic groups, with resulting implications for monitoring and prevention of this devastating pregnancy outcome.

The researchers found that the most common causes of stillbirth were obstetric conditions, such as cervical insufficiency, placental abruption, or preterm labor, and abnormalities of the placenta. Other common causes included genetic or structural abnormalities of the fetus, umbilical cord abnormalities, infection, blood pressure disorders, and other maternal medical conditions. Previous research shows that black women are more than twice as likely to be affected by stillbirth as white women, but the reasons for this disparity are as yet unknown. In this study, the researchers discovered that stillbirths in black women were more likely to occur earlier in the pregnancy or during childbirth and were more likely to be caused by obstetrical complications or infection.

"Stillbirth is more common than people realize, affecting one out of every 160 pregnancies in the United States," says Robert M. Silver, M.D., professor of obstetrics and gynecology, chief of the Division of Maternal-Fetal Medicine at the University of Utah School of Medicine, and senior author on the study. "Our research focuses on determining underlying causes of stillbirth, as well as factors that may contribute to the significant racial disparity in stillbirth rates."

There are approximately 26,000 stillbirths a year in the United States, equivalent to the number of infant deaths that occur each year. Although the stillbirth rate declined steadily from 1990 to 2003, it has remained stagnant since 2003 and is higher than that of many other developed countries. SCRN was created by the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) to address this major public health issue. The main objectives of the SCRN include ascertaining the causes and risk factors for stillbirth and finding reasons for racial disparities. For this study, the SCRN recruited a racially and geographically diverse population from 59 hospitals in five states. SCRN researchers performed complete postmortem examinations on 512 of the 972 stillbirths that occurred in the study areas from March 2006 to September 2008. These postmortem examinations included autopsy, evaluation of the placenta by a perinatal pathologist, and chromosome testing, in addition to laboratory studies and an interview with the mother. By performing systematic evaluations, the researchers were able to identify a probable or possible cause of death in 390, or 76 percent, of the stillbirths.

"Evaluations for causes of stillbirth are often incomplete or absent due to limited availability of services, concerns about cost, or difficulty in discussing death or postmortem examination," says Silver. "However, performing a thorough investigation to determine a cause may actually help to facilitate closure or alleviate guilt for patients and physicians affected by stillbirth. It can also help in counseling patients about recurrence risk and, in some cases, guide medical interventions to improve outcomes in subsequent pregnancies.

"The consistent and persistent racial disparity in stillbirth remains largely unexplained," says Silver. "It is well-documented that black women are also more likely to have spontaneous preterm birth, so perhaps there are genetic or other factors that contribute to both stillbirth and spontaneous preterm birth in black women."

A second study conducted by SCRN, also published in the same issue of JAMA, examined the relationship between stillbirths and risk factors that could be determined at the start of pregnancy. This study revealed that multiple factors, including black ethnicity, previous stillbirth, never having given birth, prior pregnancy loss, diabetes, maternal age, marital status, and excess weight, were associated with an increased risk of stillbirth. However, these risk factors accounted for only a small proportion of overall stillbirth risk.

Several reproductive factors were most strongly associated with stillbirth, including previous stillbirth, nulliparity (i.e., never having borne a child) with and without history of miscarriages at fewer than 20 weeks' gestation, and multiple births in the current pregnancy.

Other factors found to be associated with stillbirth included:
  • Non-Hispanic black race/ethnicity;
  • Obesity;
  • Diabetes;
  • Pregnancy after age 40;
  • Maternal AB blood type;
  • Not living with a partner;
  • Smoking during three months prior to pregnancy; and
  • History of illicit drug use.

"Moms-to-be and clinicians have a window of opportunity to save babies' lives by maintaining a healthy weight, managing conditions such as diabetes and stopping all unhealthy behaviors, such as smoking, prior to pregnancy. In fact, obesity may be among the greatest risk factors that we have control over," said corresponding author Dr. George Saade, Chief of Maternal-Fetal Medicine at UTMB. He added that women with any of these known risk factors should start prenatal care early and that doctors should monitor them closely.

"We were surprised to learn that while these risk factors were significant on their own, they didn't account for the largest risk of stillbirth. Even if effective, reducing modifiable risks across the board would be unlikely to prevent all stillbirths," he said. "Other factors -- perhaps occurring later in pregnancy -- may have more predictive value, either independently or combined with these early risk factors."

Ultimately, the SCRN's body of research will be used to develop a model to calculate patients' individual risks so that doctors can take appropriate steps to prevent stillbirth. These include providing those at highest risk with additional monitoring and care and improving our ability to determine the risks and benefits of delivering early versus continuing the pregnancy.

"It is extremely difficult to predict stillbirth risk based on risk factors that can be identified at the start of a pregnancy," says Silver. "The more we learn about causes and risk factors for stillbirth, the better we will become at designing strategies to reduce or prevent stillbirth."


Sources: University of Utah Health Sciences, University of Texas Medical Branch at Galveston and ScienceDaily



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