Most of the time, when you get an anti-D on an OB patient, it's passively acquired due to antepartum RhIG,
BUT, if you get reactions in any other phase other than IAT, or get reactions stronger than 2+, you may be dealing with an active immune response, and a titer would be recommended. Passively acquired anti-D rarely has a titer > 1:4, or reacts in other phases other than IAT
We have had two mothers recently, who received antepartum RhIG, but the anti-D was reacting at IS and 37. Both babies had a positive DAT with anti-D eluted. One mother had a titer of 64, the other had a titer of 256. Her baby's cells typed Rh neg, due to large amounts of anti-D coating the cells. Neither baby required transfusion. Bilirubin went from 3.2 at birth, 6.5 day 1, 14.9 day 2, then started dropping.