A 30-Year-Old Woman With an Abnormal Fetal Ultrasound

Craig Johnson, DO; Zachary Redus; Michael Mader, MD; Frederick Eruo, MD, MPH


April 25, 2017


The ultrasound demonstrated complete placenta previa (Figure 1). In addition, at the site of previous cesarean delivery, significant thinning of the uterus and loss of the uterine/placental interface was noted (Figure 2). It was also difficult to visualize a plane between the bladder and the uterus; because of this, placenta accreta or placenta percreta was suspected.

Figure 1.

Figure 2.

Figure 3.

Figure 4.

Additional Doppler imaging did not demonstrate serosal extension of the placental vascularity. The subsequent MRI scan (Figure 3) also demonstrated focal loss of the uterine/placental interface (best visualized on the T2-weighted sequences) within the lower uterine segment at the site of previous cesarean section (Figure 4), which is consistent with at least placenta accreta. No placental invasion was visualized, but the fat plane between the bladder and the uterus was not clearly identified to rule out bladder invasion.

Placenta accreta was once a rare condition but is becoming increasingly more common. This is believed to be due to a rising cesarean delivery rate.[1]Other risk factors for placenta accreta include multiparity; increasing maternal age; endometrial defects; scarring of the uterus (Asherman syndrome); and, most significantly, placenta previa.

Placenta previa is implantation of the placenta in the immediate vicinity of the cervical canal. In complete placenta previa, the placenta covers the entire opening of the internal cervical os. In partial placenta previa, the placenta partially covers the internal cervical os. Marginal placenta previa and low-lying placenta are also described; these occur when the placenta extends to the edge of the internal cervical os or within 2 cm of the internal cervical os, respectively. An important point is that most cases of complete placenta previa early in the second trimester resolve during pregnancy.[1]

Placenta accreta is one of three different types of abnormal placentation. Placenta accreta, which accounts for 75% of cases, is the most common presenting type. Placenta accreta occurs when the placental villi adheres directly to the myometrium but does not penetrate the muscular layer, with complete or partial absence of the decidua basalis. Placenta increta accounts for 15% of all cases and is characterized by the adherence of placental villi directly to the myometrium and demonstrates penetration within the myometrium. Placenta percreta, the least common of the three, involves the penetration of the placental villi into the serosal layer of the uterus. Direct attachment to adjacent organs may also occur.

Although these three types of abnormal placentation are characteristically different, the literature often refers to them collectively as "placenta accreta."

The clinical history in this particular case is extremely important, because the risk for placenta accreta is approximately 40% in a patient with placenta previa and a history of two previous cesarean deliveries. Imaging can help raise or lower the concern for placenta accreta in high-risk patients, but it is not usually definitive, which limits its ability to change management in these patients.


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