My aunty has coeliac disease (which causes problems with digesting gluten) and she had two miscarriages and when her second son was born he was full term but very low birthweight and his placenta was really small. My aunt remembers the doctors calling others in to look at it after it came out they had never seen such a small one.
After she was diagnosed with coeliac disease she was told it was likely the cause of this and her miscarriages. So definitely something worth looking at since gluten intolerance and coeliac disease aren't exactly uncommon.