Wexler P, Gottesfeld K R
Obstet Gynecol. 1979 Aug;54(2):231-4.
Ultrasound was used as a diagnostic tool in 859 patients for the localization of the placenta in the second trimester prior to genetic amniocentesis. A greater incidence of total placenta previa was found in the study group (5.6%) than is reported for the general population (0.25-0.5%). Maternal age greater than 35 years was the indication or co-factor in 59% of the patients studied, which might explain this difference. It was possible to predict total placenta previa at term early in the second trimester. It was demonstrated that if a placenta was located centrally over the cervical os and did not change position with variations in the degree of bladder-filling or changes in uterine position, the risk of having a total placenta previa at term increased from 1/143 to 1/8 pregnancies.
在859例患者中，超声被用作妊娠中期基因羊膜穿刺术前胎盘定位的诊断工具。研究组完全性前置胎盘的发生率（5.6%）高于一般人群报道的发生率（0.25 - 0.5%）。在59%的研究患者中，母亲年龄大于35岁是指征或辅助因素，这可能解释了这种差异。在妊娠中期早期就有可能预测足月时的完全性前置胎盘。结果表明，如果胎盘位于宫颈口中央，且不随膀胱充盈程度或子宫位置的变化而改变位置，足月时发生完全性前置胎盘的风险从1/143增加到1/8妊娠。
