VTE Risk Higher in Patients With Placenta Accreta

MINNEAPOLIS — Risk for venous thromboembolism (VTE) appears substantially greater in patients with placenta accrete than in other pregnant patients, found a small single-center study presented at the American College of Obstetricians and Gynecologists (ACOG) 2025 Annual Meeting.

Despite the institution having created a specific protocol — a VTE bundle — for patients with placenta accreta, only about one in five patients with placenta accreta received the complete bundle, reported Rinat Tal, of the University of Michigan Medical School, Ann Arbor, Michigan, and colleagues. 

“Patients with placenta accreta spectrum are at risk for massive hemorrhage, need for blood transfusion, massive transfusion, long operating times, general anesthesia, and ICU stay, all of which increased patients’ risk for VTE beyond the preexisting elevated risk in pregnancy,” the authors wrote. 

Yet, guidelines do not exist regarding the optimal VTE prophylaxis for patients with placenta accreta, they noted. So, the researchers assessed the effectiveness of a VTE bundle developed at their institution for reducing risk for VTE in patients with placenta accreta.

The Michigan Medicine VTE Bundle included four components: Intraoperative administration of subcutaneous heparin; anticoagulation restarted within 8 hours postoperatively; anticoagulation continued through discharged; and prophylactic anticoagulation prescribed at discharge.

The authors analyzed retrospective data on all scheduled cesarean hysterectomies performed for suspected placenta accreta, excluding patients with cancer and those with incomplete 6-week postpartum data. They identified 90 patients who met their criteria and found that only 22.2% had received the complete VTE bundle.

Incidence of VTE was 2.2% in the cohort: One patient who received the complete bundle and one who did not (P = .34). The groups therefore showed no difference in risk-based receipt of the complete bundle, but the population was likely too small, especially for such a rare outcome, to achieve statistical power in the study. The researchers noted, however, that the incidence of VTE was 18 times higher in this cohort than in pregnant patients generally.

Among the 77.8% of patients with placenta accreta who did not receive the full VTE bundle, 28.5% had a delayed restart of postoperative anticoagulation but otherwise received the other three components of the bundle. However, the other 71.4% were missing anywhere from one to three components, including 5.7% who received no prophylactic anticoagulation. 

The women who did and did not receive the VTE bundle had a similar age, a median 34 years old, and gestational age at delivery was a median 34 weeks. However, the median body mass index of women who received the bundle was 34.7 compared with 31.8 among those receiving incomplete bundles. Also, more of the women receiving an incomplete bundle had a previous C section (92.9%) than those who received the full bundle (80%). 

Median blood loss was greater in those who received an incomplete bundle (2500 mL) than those who received the full bundle (1600 mL), and more women receiving an incomplete bundle (21.4%) had a packed red blood cell transfusion than those who received the full bundle (5%).

The researchers suggested additional research to evaluate the barriers to providing all appropriate patients with the VTE bundle and targeted quality improvement efforts to improve compliance. 

Alison G. Cahill, MD, associate dean of translational research and professor of women’s health at The University of Texas at Austin Dell Medical School, told Medscape Medical News that the findings here need to be interpreted cautiously given that it’s such a small study and results are only currently available in the poster. Regardless, the question the researchers ask is an important one that should merit investigation, Cahill suggested. 

“We’re constantly searching for opportunities to further reduce the chance of VTE in the setting of pregnancy for all kinds of all pregnant people,” Cahill said. This study “raises the question as to whether or not this group [those with placenta accreta] should be considered separately” in seeking more ways to prevent VTE, she said.

“Just the idea of thinking about VTE risk — that there are differences, and what they look like, and how we might approach them differently — is an important investigative lane, especially because a lot of the data that we have for VTE primary prevention is from outside of the obstetric literature,” Cahill said. 

No external funding or disclosures from the authors were reported. Cahill had no disclosures. 

Tara Haelle is a science/health journalist based in Dallas.