I can understand your concerns,as far as the darker facial complexion you are referring to is due to the hormonal
changes in the body during pregnancy
and one can't do much about it until the pregnancy is over.
Secondly you cannot change or modify the complexion of the baby,it's something genetic although you should take multivitamins and Folic Acid
advised by ur doctor to keep yourself and the foetus
I hope you would understand my point here.
Thanks very much and all the best.