metformin not letting my baby grow??

I have GD since week 24, was put on metformin 10 days back post. Until then my baby was growing well even though I was controlling my diet. But after starting metformin, it seems my baby has stopped growing and no increase in weight. 10 days back she measured 29 weeks 1400gms and today she measured 29wks 1200 GMs which is so strange. My OB said metformin can cause smaller babies but I didn't find this info on Internet.