Placenta accreta spectrum (PAS) used to be a rare pregnancy condition, but now affects approximately 14,000 pregnancies annually, being a leading cause of maternal death. However, why this happens is still not well understood. Placenta accreta occurs when the placenta grows too deep into the uterine wall and does not detach after birth, often resulting in life-threatening bleeding and the need for a hysterectomy.
The strongest and most common risk factor is a previous C-section, as scars from previous C-sections can change the way the placenta attaches in future pregnancies. New research led by UCLA Health suggests that how this scar tissue heals could be the key to better understanding how PAS develops, who is at risk and why the placenta attaches abnormally.
“Our findings show that the main problem in placenta accreta is not the placenta growing abnormally—it’s how uterine scarring changes the structure and organization of collagen in the uterus to increase the risks of delivery,” said Yalda Afshar, MD, associate professor of obstetrics and gynecology in the DavidLAC School of Maternal Medicine department at the U.S., co-director of the UCLA Health Accreta Care Program and corresponding author of the study.
The study, published in American Journal of Obstetrics and Gynecologyused surgical specimens, a mouse model, and an accreta-in-a-dish laboratory system to investigate how collagen structure, when tangled or irregular, rather than properly aligned, contributes to abnormal placental attachment. Through advanced 3D imaging, researchers found that tangled or irregular collagen in old uterine scars breaks down the normal boundary between uterus and placenta, creating a permissive environment for abnormal placental attachment and creating a high-risk birth.
The researchers collected samples from 13 patients with PAS and 10 with risk factors for accreta but without PAS, taking tissue from where the placenta attached and from where it did not. Their findings showed that persistent inflammation and immune cells called macrophages interfere with normal scar remodeling, leading to abnormal collagen architecture that promotes abnormal placental attachment.
Not all scars heal the same way. This work explains why some patients with a previous caesarean section develop placenta accreta while others do not, and points to new ways in which we can identify risk earlier, before pregnancy or early in pregnancy.”
Yalda Afshar, MD, associate professor of obstetrics and gynecology, division of maternal-fetal medicine, David Geffen School of Medicine, UCLA
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