Abstract
To assess and compare the sensitivity and specificity of ultrasonography and magnetic resonance imaging in the diagnosis of placenta accreta in patients with placenta previa. This retrospective cohort study included 37 women, and was conducted between January 2013 and October 2015; 16 out of the 37 women suffered from placenta accreta. Histopathology was considered the gold standard for the diagnosis of placenta accreta; in its absence, a description of the intraoperative findings was used. The associations among the variables were investigated using the Pearson chi-squared test and the Mann-Whitney U-test. The mean age of the patients was 31.8 ± 7.3 years, the mean number of pregnancies was 2.8 ± 1.1, the mean number of births was 1.4 ± 0.7, and the mean number of previous cesarean sections was 1.2 ± 0.8. Patients with placenta accreta had a higher frequency of history of cesarean section than those without it (63.6% versus 36.4% respectively; p < 0.001). The mean gestational age at birth among women diagnosed with placenta previa accreta was 35.4 ± 1.1 weeks. The mean birth weight was 2,635.9 ± 374.1 g. The sensitivity of the ultrasound was 87.5%, with a positive predictive value (PPV) of 65.1%, and a negative predictive value (NPV) of 75.0%. The sensitivity of the magnetic resonance imaging was 92.9%, with a PPV of 76.5%, and a NPV of 75.0%. The kappa coefficient of agreement between the 2 tests was 0.69 (95% confidence interval [95%CI]: (0.26-1.00). The ultrasound and the magnetic resonance imaging showed similar sensitivity and specificity for the diagnosis of placenta accreta.
Highlights
Placenta accreta is characterized by an anomalous adherence of the placenta to the uterine wall
The global incidence of placenta accreta has been increasing over the years; this seems parallel to the increased rate of cesarean sections (C-sections)
Wu et al[2] reported the global incidence of placenta accreta as 1:533 pregnancies between 1982 and 2002, which is much higher than the incidences of 1:4,027 and 1:2,510 reported in the 1970s and 1980s
Summary
Placenta accreta is characterized by an anomalous adherence of the placenta to the uterine wall. Ultrasound (US) criteria are used to diagnose placental invasion, namely loss of the hypoechoic retroplacental myometrial zone, thinning or disruption of the uterine serosa– bladder interface, presence of exophytic zones and large sonolucent areas in the placenta, myometrial thickness < 1 mm, and, in Doppler US, turbulent flow of placental lacunae and bladder–uterine serosa interface hypervascularity.[3,4,5]. The MRI does not seem to increase the possibility of diagnosing anterior placenta accreta; it is indicated for cases of posterior placenta, for which visualization by US is difficult owing to fetal parts.[6]
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