PIRI and S/D of fetal artery were found to become low when the pregnant days increased in normal pregnancy.

• 发现正常妊娠时胎儿脐动脉的搏动指数、阻力指数、收缩期最高峰值血流速度/舒张末期最低血流速度比值随孕龄的增加而下降；