I have thoughts on this but have not found anything scientific to back up my personal findings:

My one child was born very healthy (7 1/2 lbs, 22 inches long, immediate 9/10 on apgar) but began to 'fail to thrive' (gained only 1/2 expected weight) within 2 weeks of being born even though I had what would probably be considered an 'oversupply' of milk.

For three years, he only gained 1/2 the weight he should've. For the last three years, off gluten and other foods, his bone growth has shot up but his weight, though steady, has not increased as expected (which is what happens with children who have 'simple' celiac).

Therefore, I think that the sensitivity may be inherited but there may be a lot of 'filters' in place within the mother's system... then once outside in the real world, the molecules, dust, etc. that will invariable enter the baby's system, unfiltered, and have a more profound effect on the infant's system.

That's what I think happened to my son, anyway. He did have many other 'allergies' right off the bat too though and I think 'unfiltered' exposure to all of them took it's toll.