Unusual features of the human placenta may be the underlying cause of postpartum hemorrhage, the leading cause of maternal deaths during childbirth, according to evolutionary research at the University of Illinois at Chicago.
Defined as the loss of more than a pint of blood during or just after vaginal delivery, postpartum hemorrhage accounts for nearly 35 percent, or 125,000, of the 358,000 worldwide annual maternal deaths during childbirth.
Despite its prevalence, the causes of postpartum hemorrhage are unknown, says Julienne Rutherford, assistant professor of oral biology at UIC, who along with Elizabeth Abrams, assistant professor of anthropology, co-authored a theoretical synthesis published in the journal American Anthropologist. While common in humans, postpartum hemorrhage is rare in other mammals, including nonhuman primates.
"Understanding the underlying cause of the increased risk of postpartum hemorrhage in humans is a critical step toward discovering new treatments and eventually preventing it on a global scale," Rutherford said.
Previous studies on postpartum hemorrhage have focused on how it can be treated and on recognizing its associated risk factors, Abrams said. Less has been done to discover its cause.
In humans, the invasiveness of the placenta into the uterine wall and the subsequent takeover of maternal blood vessels appear to be greater than in nonhumans, Rutherford said. This suggests a link between placental invasiveness early in pregnancy and blood loss at delivery, when the placenta separates from the uterine wall.
Research by Abrams and Rutherford suggests that hormones produced by trophoblasts -- cells formed during the first stage of pregnancy that provide nutrients to the embryo and develop into a large part of the placenta, and that guide the interaction with the uterus -- may provide an early predictor of risk.
"Biomarkers of postpartum hemorrhage that could
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University of Illinois at Chicago