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ABSTRACT: Cell damage is a natural part of fetal development, and the embryo and fetus have some self-repair ability. Studies indicate that ultrasound imaging and Doppler applications do not harm by heating where circulation exists to dissipate heat. The shortness of the ultrasound pulses mitigates against cell damage by cavitation. Ultrasound scans are often recommended at 16 to 18 weeks LMP, when the most vulnerable fetal organ is the forebrain, or at 32 to 34 weeks LMP, when the fetal cerebellum is vulnerable and defects in vision or hearing are possible. Negative animal experiments cannot show damage of rates less than I in 1000. When considering possible links between ultrasound and childhood cancers or development defects, risk levels cannot be assessed until a large, adequately designed, randomized controlled trial with sufficient follow-up is conducted.