I have heard the same thing regarding metformin... it does help reduce the chance of miscarriage and it quite safe to be continued up to 12 weeks.

I'm 5 weeks today after my first IVF transfer... and I'm sticking with the metformin!

One of my oldest and closest friends is an ob/gyn registrar - she checks all my meds for me against current literature and I'm assured that it's all ok... and my FS agrees.

BW