Methods Samples of peripheral blood in 64 women of 8-40 gestational weeks were collected to enrich the fetal nucleated red blood cells by density gradient centrifugation.

• 方法对64例孕8-40周孕妇外周血进行密度梯度离心法，富集胎儿细胞，并经显微镜下观察计数各种细胞所占百分比。