Worked after 30 weeks

I got this app around 16 weeks and tested it fairly regularly but its true what the app says, works best after 30 weeks.
My phone is a 5s and works fine.
Ive been able to find babys heartbeat easily in the last two months. They are frequently in the anterior position which I assume helps to hear it more than if its back was turned away from where you place the phone.

Alex&Colin about MyBabysBeat - Fetal heartbeat, v2.5