“You think of pregnancy as joy, laughter, preparation for a new life. Never did I think it was possible that I could risk losing my uterus or my life because of pregnancy.”
If I had a nickel for every time I heard this from a patient diagnosed with the placenta accreta spectrum (PAS)…
Many have never heard of PAS, where the placenta grows past the endometrial lining of the uterus and into or beyond the uterine wall. Blood vessels tend to be engorged due to the increased uterine blood supply to support pregnancy. New, abnormal vessels are recruited. This makes surgical management tricky at best and the risk for massive hemorrhage a reality at worst.
The good news is that antenatal identification of PAS has been proven in multiple observational studies to lead to improved outcomes. Why? Antenatal detection allows patients to be referred to centers with experienced, multi-disciplinary PAS teams.
In the U.S., a majority of patients with PAS undergo a cesarean hysterectomy, the definitive surgical approach. Other centers may offer alternative approaches, including delayed hysterectomy, partial myometrial resection, or truly conservative management, where the placenta is left in place after delivery until the placenta resorbs, gets expelled, or complications arise. No matter the approach, the risk for major morbidity and mortality is proven to be lower when patients are cared for by experienced, multidisciplinary teams.
PAS encompasses placenta accreta, increta, and percreta, and truly represents a broad spectrum of abnormal placentation.
Why the sudden interest in PAS?
Many experts believe that the incidence of PAS is rising worldwide. Most large population-based studies show that the incidence ranges more consistently between 1 in 1000 to 5 per 10,000 pregnancies. While these rates are lower than traditionally cited (1 in 200 to 500 deliveries, as cited from referral centers), the increased risk for morbidity and mortality drive the need for vigilance when evaluating patients. PAS can be detected with ultrasound with 80–95% sensitivity and specificity in expert centers, but the overall antenatal detection rate runs closer to 40–50% according to population-based studies.
How is PAS detected before delivery?
Ultrasound is the cornerstone, as it is noninvasive, relatively inexpensive, and readily available. Some experts consider referral to MRI if the placenta is not adequately seen. MRI is not a superior, however, but rather it permits visualization of the placenta in a different way. The sensitivities and specificities of ultrasound and MRI are similar. As with imaging modality, diagnostic accuracy depends upon the expertise of the people acquiring and interpreting the images. Referral to experienced imaging centers is recommended for patients with significant risk factors or if PAS is suspected.
What are the risk factors for PAS?
Most commonly, previous cesarean deliveries and placenta previa. Other risk factors include myomectomy, endometrial ablation, smoking, and in vitro fertilization.
How can we improve antenatal ultrasound detection?
Using standardized protocols and checklists to “prime the mind” are important. One cannot find what one does not seek, therefore, it is important to evaluate the placenta thoroughly.
A few quick tips:
- Fill the bladder. The full bladder creates an acoustic window that improves visualization of the lower segment. Irregular placental bulging and hypervascularity can also be seen with better accuracy.
- Angle matters. The lower uterine segment curves away from (perpendicular to) the transabdominal probe. This causes shadowing. Position the patient bed head down and angle the probe such that the handle parallels the patient’s thighs and the lowermost segment appears clearly.
- Image transvaginally. Using a transvaginal approach identifies deep, cervical invasion and can provide a clear view of the lower uterine segment.
- Interrogate the ENTIRE placental surface. Sweep sagitally left to right, transversely both the midline and along each (to look for parametrial involvement).
- 3D and color Doppler. These imaging tools can help identify hypervascularity and bladder contour irregularities.
If there were ever a silver lining, the spotlight on PAS as is fueling us all to work to identify best practices and to improve training at all levels.
Karin A. Fox, MD, MEd, FACOG, is an Associate Professor, Associate Fellowship Director, and Clinical Director of the Placenta Accreta Spectrum Care Team in the Division of Maternal-Fetal Medicine, Department of OB-GYN, at Baylor College of Medicine, as well as is Medical Director of Maternal Transport for the Kangaroo Crew at Texas Children’s Hospital Pavilion for Women.
Interested in learning more about placenta accreta spectrum? Check out the following resources:
- American Institute of Ultrasound in Medicine (AIUM) webinar: Saving Lives With Ultrasound: How to Improve Antenatal Detection, Risk Stratification, and Placenta Accreta Spectrum Management
- Journal of Ultrasound in Medicine (JUM) article: Prospective First‐Trimester Ultrasound Imaging of Low Implantation and Placenta Accreta Spectrum
- Pan-American Society for the Placenta Accreta Spectrum
- Journal of Ultrasound in Medicine (JUM) article: Placenta Accreta Spectrum 2021: Roundtable Discussion
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