Antibodies in my blood during pregnancy?

I am now 13 weeks pregnant, when I was about 8 weeks pregnant the doctor had to take alot of blood to see if antibodies in my blood matched up. Him and my own personal doctor asked if I had ever had any blood transfusions before and I haven't. They did send it back to a lab and the antibody was unknown. Before I was pregnant, they didn't find any of these antibodies. Has anybody had this? Is it a serious problem? The doctor had also said he'd have to make sure the hospital knew about them for when I gave birth..