As a hardware and software professional, this headline sounds like 100% bullshit.
allows your phone to measure prenatal heartbeat
That is not the same thing as an ultrasound scanner.
It’s a microphone app which trims to, and amplifies, specific frequencies which allows you to monitor the baby’s pulse.
You absolutely can use your phone with an ultrasound scanner, but this requires external hardware which, while not restricted, is not super cheap.