Doppler ultrasonics provides the first positive sign of pregnancy. Fetal cardiovascular activity can usually be detected shortly after the second missed menses. At 11 weeks of pregnancy, fetal life can be proven in 90% of patients, and after 17 weeks, in 100%. The ultrasonic Doppler diagnostic instrument is of great value in threatened abortion, missed abortion, and in amenorrhea in patients with marked obesity or fibroid uteri. It is also valuable in determining fetal position in diagnosing twins, and in finding the placental site.
Lloyd TS. Obstetrical Use of the Ultrasonic Doppler Instrument. JAMA. 1968;204(13):1195–1196. doi:10.1001/jama.1968.03140260035016
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