I've had a quick look through the uni database and there seems to be a small suggested link between maternal ovarian stimulation and lower birth weights. So if IVF is done through a frozen transfer then there is no difference in birth weights, equally if the pregnancy results from egg donation as the donor is the one who went through ovarian stimulation. However the link is not universally accepted yet (from what I can understand) but the main take away point is that most babies, whether through IVF or not, are born healthy.