The AABB TM, 18th edition, states in Chapter 22, Perinatal Issues in Transfusion Practice, Serology and Mechanism, "Administration of RhIG during pregnancy may produce a positive antibody screening result in the mother, but the titer is rarely greater than 4 and thus poses no risk to the fetus."
If we ID anti-D in prenatal sample, we perform a 1:4 dilution and if the results are non-reactive we have two statements in our report, "The antibody demonstrated a titer of less than 4 in saline at AGT indicating that it may be due to recent administration of RhIG." and "Due to the recent administration of RhIG, the antibody may have been passively acquired. To establish this as the sole cause of the antibody's presence, repeat testing six months post-delivery should demonstrate a negative antibody screen."