Lower uterine segment placental thickness in women with abnormally invasive placenta

Ultrasound signs of abnormal placental invasion are subjective in nature. We tested the hypothesis that placental thickness in the lower uterine segment is increased when there is abnormally invasive placenta (AIP) in women with a low-lying placenta.

Retrospective analysis of data of placental thickness in women with ultrasound evidence of major placenta previa or a low-lying anterior placenta was done. The diagnosis of AIP was confirmed both intraoperatively and on histopathology for those managed by partial myometrial excision with uterine conservation or by hysterectomy.

In all, 131 records were available for analysis after exclusion of 33 cases due to unsuitable images and eight cases without pregnancy outcomes. The diagnosis of AIP was confirmed in 28 (21.4%) of the 131 cases. The lower segment placental thickness was significantly higher in women with AIP (median = 50.3 mm, IQR: 42.7-64.3) than in those with normal placentation (median = 30.9 mm, IQR: 22.9-42.2, P < 0.001). Logistic regression analysis showed that previous cesarean section and placental thickness on ultrasound were independent predictors for AIP.

Lower uterine segment placental thickness is increased in women with AIP compared with those with noninvasive placentation. This association constitutes a pragmatic objective sign and may be of clinical value in improving prenatal detection of AIP in women with placental implantation in the lower uterine segment. Prospective studies are necessary to ascertain lower segment placental thickness as a predictor for AIP.