Zelop C C, Bromley B, Frigoletto F D, Benacerraf B R
Department of Obstetrics and Gynecology, Brigham & Women's Hospital, Harvard Medical School, Boston, MA.
Int J Gynaecol Obstet. 1994 Mar;44(3):207-10. doi: 10.1016/0020-7292(94)90167-8.
We sought to determine the natural history of second trimester sonographically diagnosed placenta previa, and to ascertain whether the position of the placenta with respect to the cervical os at second trimester sonography can accurately predict persistence of the placenta previa at term.
The study population included all women consecutively diagnosed by ultrasound with placenta previa between 14 and 20 weeks' gestation. Medical records of the patients requiring cesarean section were reviewed to determine the presence of placenta previa. We reviewed the second trimester sonogram of patients who underwent abdominal delivery for placental and nonplacental indications to determine whether the central (symmetrical) versus the partial (asymmetrial) position of the placenta with respect to the internal os predicted the presence of placenta previa at delivery.
A total of 925 second trimester- patients were sonographically identified as having placenta previa. Two hundred and sixty seven patients underwent cesarean delivery, 43 of which had placenta previa (43/925 or 4.6%). Twenty-two of the 43 were asymptomatic without antepartum bleeding. Analysis of the second trimester position of the placenta revealed that symmetry of the placenta with respect to the internal os at second trimester scan had a sensitivity of 49% for prediction of placenta previa at birth.
The degree of placental symmetry with respect to the internal os during the second trimester successfully predicted the previas most likely to persist at delivery with a sensitivity of 49% (95% CI 34-64) and specificity of 93%.
我们试图确定孕中期超声诊断前置胎盘的自然病史，并确定孕中期超声检查时胎盘相对于宫颈内口的位置能否准确预测足月时前置胎盘的持续存在情况。
研究人群包括所有在妊娠14至20周期间经超声连续诊断为前置胎盘的女性。对需要剖宫产的患者的病历进行回顾，以确定前置胎盘的存在情况。我们回顾了因胎盘和非胎盘指征行剖宫产的患者的孕中期超声图像，以确定胎盘相对于宫颈内口的中央（对称）与部分（不对称）位置是否能预测分娩时前置胎盘的存在。
共有925例孕中期患者经超声检查诊断为前置胎盘。267例患者接受了剖宫产，其中43例有前置胎盘（43/925，即4.6%）。43例中有22例无症状，无产前出血。对孕中期胎盘位置的分析显示，孕中期扫描时胎盘相对于宫颈内口的对称性对预测出生时前置胎盘的敏感性为49%。
孕中期胎盘相对于宫颈内口的对称程度成功预测了最有可能在分娩时持续存在的前置胎盘，敏感性为49%（95%可信区间34 - 64），特异性为93%。
