A specialist physician may request blood group and Rh factor testing during pregnancy to detect Rh incompatibility. This test, which determines whether an individual is Rh-positive or Rh-negative, is typically performed as part of routine first-trimester blood work. However, it may be conducted earlier if vaginal bleeding occurs. If the pregnant individual's blood is found to be Rh-negative, the physician may request an additional test called an antibody screen. This test checks for the presence of Rh antibodies in the blood. If the antibody test is positive, it indicates a risk of Rh sensitization. If negative, Rh immunoglobulin (RhIg) is administered to prevent antibody formation. RhIg is usually given around the 28th week of pregnancy and within 72 hours after birth, but it can be administered earlier if the pregnant individual experiences bleeding or other complications.