I quizzed FS about this (yep, I was one of "those" patients!)

Her take was that IVF bubs aren't from "normal" parents usually. So there are factors like maternal age, and also all the other reasons that getting pg in the first place was harder etc. She also said that she had once had some numbers crunched on the clinics outcomes where it was male factor infertility and when they did that there was no statistically significant difference in birth weight to a natural conception so my clinic decided that it wasn't the IVF as such that was the factor in lower birth weights, rather the other factors.

Does that make sense? Help?