Placenta accreta is a serious pregnancy complication where the placenta attaches too deeply into the wall of the uterus. Normally, the placenta detaches easily from the uterine wall after childbirth, but with accreta, part or all of the placenta remains firmly attached. This can lead to severe, life-threatening bleeding after delivery, often requiring blood transfusions or, in some cases, surgical removal of the uterus (hysterectomy). Understanding its risk factors is important for early detection and management. This article explores these factors.
Uterine Scarring and Damage
Previous uterine surgeries are the primary risk factor for placenta accreta, with Cesarean sections (C-sections) a primary concern. An incision in the uterine wall can lead to scarring during healing. This scar tissue can alter the normal uterine lining, known as the decidua, which typically acts as a barrier to prevent the placenta from invading too deeply.
If a subsequent pregnancy implants over this scarred area, the placenta’s villi can grow directly into the muscular layer of the uterus (myometrium) or even beyond, as the protective decidual layer is compromised or absent. The risk of placenta accreta increases with each additional C-section, with the risk exceeding 50% for women with two or more prior C-sections and placenta previa. Over 60% of cases involve multiple prior C-sections.
Other uterine procedures can also contribute to scarring and increase the risk. These include myomectomy (surgical removal of uterine fibroids), and dilation and curettage (D&C), a procedure to remove uterine tissue, often after miscarriage or for heavy bleeding. Endometrial ablation, a procedure to treat heavy menstrual bleeding by removing the uterine lining, can similarly cause scarring that predisposes a woman to placenta accreta.
Placental Positioning Issues
The position of the placenta within the uterus plays a significant role in the risk of placenta accreta. Placenta previa, a condition where the placenta partially or completely covers the cervix, is a major risk factor. In a typical pregnancy, the placenta attaches to the top or side of the inner uterine wall. However, with placenta previa, the placenta implants in the lower uterus, near or over the cervical opening.
When placenta previa is present, particularly in combination with prior uterine scarring from a C-section, the risk of accreta increases substantially. The placenta may implant over the scar, allowing villi to invade the uterine wall more readily due to altered tissue. This abnormal positioning creates a pathway for the placenta to grow too deeply, leading to conditions like placenta accreta, increta (deeper invasion into the uterine muscle), or percreta (invasion through the uterine wall and potentially into nearby organs like the bladder).
Maternal and Fertility Factors
Several other factors related to the mother’s characteristics and conception method can also increase the risk of placenta accreta. Advanced maternal age, over 35, is a recognized risk factor. As women age, changes in uterine blood vessels and overall uterine health may contribute to abnormal placental implantation.
Multiparity (multiple previous pregnancies) is another factor associated with a higher risk. The more pregnancies a woman has had, the greater the potential for subtle changes or cumulative effects on the uterine lining that could increase the risk of abnormal placental attachment. Additionally, Assisted Reproductive Technologies (ART), such as in vitro fertilization (IVF), has been linked to an increased risk of placenta accreta. While the exact reasons are still being studied, it is thought that the procedures involved in ART, including embryo transfer, might slightly alter the uterine environment, making it more susceptible to deep placental implantation.
Why Understanding Risks Matters
Recognizing placenta accreta risk factors early in pregnancy is beneficial for both maternal and fetal well-being. An early diagnosis, often made through routine ultrasound, allows healthcare providers to implement closer monitoring throughout the pregnancy. This proactive approach helps prepare for a safer delivery, as a multidisciplinary team (including obstetricians, maternal-fetal medicine specialists, and anesthesiologists) can be assembled.
Knowing the risks enables careful planning for the timing and method of delivery, often involving a scheduled Cesarean section at a specialized medical center equipped for complications. This preparation helps mitigate severe outcomes, such as excessive bleeding and the need for a hysterectomy. Early identification and comprehensive planning improve safety for both mother and baby.