November 8, 2023 mygyno Blood group typing in pregnancy is important for various reasons. Standard blood groups are A, B, AB or O. Each group is additionally labelled either positive (+) or negative (-), which denotes what is called Rhesus factor. The Rhesus factor is a marker on the red blood cells, and majority of people have this factor and are labelled Rhesus positive. However, about one in every ten people are Rhesus negative.