Continuous ultrasound and fetal movement.

@article{Hertz1979ContinuousUA,
  title={Continuous ultrasound and fetal movement.},
  author={R. H. Hertz and I E Timor-Tritsch and Leroy Dierker and L C Chik and Mortimer G Rosen},
  journal={American journal of obstetrics and gynecology},
  year={1979},
  volume={135 1},
  pages={152-4}
}