Hi
My aunt had the same issue. She has coeliac disease and had two miscarriages which her doctors blamed on it.
Her second son's placenta was also very, very small when he was born at full term which they said could also have been a result of it as well.
But the good news is that she has two healthy boys so don't give up hope. I hope next time works out better, I'm sorry you lost your twin babies. Take care.