Why would my doctor have acess to my prenatal care ysis??

Today I went to my primary care doctor and while waiting to be seen by him, I couldn't help but notice my chart laying around. Curiousity consumed me, and I took a lil sneak peak. I was extremely surprised to find my prenatal lab results in his chart. I was very shocked due to the fact that my prenatal care providres and my private doctor are two seperate facilities I visit routinely. Why is it that he had my results in his chart from test that were performed on me by my prenatal care??