Here is one very good article from the VDC which supplies a lot of good information http://www.vitamindcouncil.org/further-topics/vitamin-d-during-pregnancy-and-breastfeeding/.
Also http://www.ncbi.nlm.nih.gov/pubmed/17661565 is a very good study. Basically this study proves that Vitamin D does not show up in a mother’s breast milk until the mother reaches a blood level of about 40 – 50ng/ml. In order to maintain this blood level you have to take around 6000iu a day of D3. (Not D2.) To get to this level “faster” you would need to take a higher amount of Vitamin D for awhile then cut back to the 6000iu.If you are overweight you may need to take even more.
For $50.00 you can become a VDC member and read the 178 results for Vitamin D and pregnancy. It is astonishing!