Final answer:
Auscultation of the fetus for heart rate is most effectively performed on the fetus's chest, where the heartbeat is most readily detected, although during prenatal checkups, the stethoscope or Doppler is placed on the mother's abdomen.
Step-by-step explanation:
Auscultation of the fetus is best performed on the part of the fetus where the heartbeat can be most readily detected. Considering the position of the fetal heart, auscultation is most effective when done on the chest of the fetus. This is because the fetal heart, like in adults, is located in the thoracic cavity.
Additionally, during prenatal checkups, healthcare providers commonly utilize a stethoscope or Doppler ultrasound device to listen to the fetal heart rate by placing it on the mother's abdomen, over the area where the fetal back, and consequently the chest, is closest to the abdominal wall.
For clinical reference, the stethoscope's placement on the newborn infant's chest, as seen in the Apgar test immediately after birth, denotes the standard practice of auscultation to assess heart rate—one of several important health indicators in neonates.