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© 2005 by the American Institute of Ultrasound in Medicine
J Ultrasound Med 24:331-335 • 0278-4297

A Small-Angled Thin Edge of the Placenta Predicts Abnormal Placentation at Delivery

Ken-ichi Shukunami, MD, Koji Nishijima, MD, Tetsuji Kurokawa, MD, Kimihisa Tajima, MD, Naoyuki Kamitani, MD, Yoshio Yoshida, MD and Fumikazu Kotsuji, MD, PhD

Department of Obstetrics and Gynecology, University of Fukui, Fukui, Japan (K.S., K.N., T.K., K.T., Y.Y., F.K.); and Department of Obstetrics and Gynecology, Fukuiken Saiseikai Hospital, Fukui, Japan (N.K.).

Address correspondence and reprint requests to Ken-ichi Shukunami, MD, Department of Obstetrics and Gynecology, University of Fukui, Matsuoka-Cho, Yoshida-Gun, Fukui 910-1193, Japan. E-mail: forton{at}fmsrsa.fukui-med.ac.jp

Objective. This study was intended to determine the relationship between the angle of the lower placental edge in early pregnancy and the previa/low-lying placenta at delivery. Methods. We used transvaginal sonography to consecutively screen 2543 singleton pregnancies. All subjects were scanned during the period of gestation between 12 weeks 0 days and 15 weeks 6 days. The angle of the lower placental edge was measured when the placenta covered the internal cervical os. These cases were followed sonographically until term. Results. Of 168 cases in which the internal cervical os was covered at screening, 9 showed previa/low-lying placenta at delivery (previa/low-lying group). The remaining 159 showed no abnormal placentation (nonprevia group). There were significantly fewer degrees of angle in the previa/low-lying group than in the nonprevia group (P < .05). For the previa/low-lying group, the arithmetic mean, median, and SD values of the angles were 60.8°, 50.0°, and 9.8°, respectively. For the nonprevia group, those values were 103.4°, 103.0°, and 31.8°, respectively. Data based on the cutoff number of the angle of 74° indicated the following: sensitivity of placenta previa or low-lying placenta at term, 100% (9 of 9); false-positive rate, 23% (36 of 159); positive predictive value, 20% (9 of 45); and negative predictive value, 100% (123 of 123). Conclusions. The angle between the placental-uterine interface and fetal placental surface can be evaluated during early pregnancy. It appears to accurately predict placenta previa or low-lying placenta at term gestation with a sensitivity of 100%, a false-positive rate of 23%, and a high negative predictive value of 100%, which would allow for elimination of some of the multiple scans.

Key Words: angle • low-lying placenta • placenta previa • predict

Abbreviations: ROC, receiver operating characteristic

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Copyright © 2005 by the American Institute of Ultrasound in Medicine.