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Representative immunostaining images of the proliferation marker Ki-67 in HDF cells, 24 h after exposure to (A) 0 min (control) (B) 10 min (C) 20 min, and (D) 30 min 4D mode of second-trimester fetal sonography condition. (E) Quantification of Ki-67-positive cells after exposure to different times of 4D mode of diagnostic ultrasonography. Data represent the mean ± SD of three independent experiments.* P < 0.05; ** P < 0.01.
