By the twelfth week of pregnancy, fetal heartbeats can be detected using a Doppler ultrasound device
by a physician
by a physician
This sentence has a misplaced modifier
The phrase 'by the twelfth week of pregnancy' is not modifying fetal heartbeats instead it should modify the noun 'Physician'
So it should read as follows
By the twelfth week of pregnancy, a physician can detect fetal heartbeats using a Doppler ultrasound device
