A newly developed high-speed ultrasound imaging system enabled accurate observations to be made of fetal respiratory movements in utero. Visual monitoring of data acquisition eliminated artifactual recording.
(JAMA 240:35-36, 1978)
Stephens JD, Birnholz JC. Noninvasive Verification of Fetal Respiratory Movements in Normal Pregnancy. JAMA. 1978;240(1):35–36. doi:10.1001/jama.1978.03290010039019