We have been having a discussion about when a Kleihauer-Betke stain (or even flow cytometry for fetal cells) becomes a worthwhile test to perform. We already do not perform a fetal screen (rosette test) at less than 20 weeks gestation, and only give one vial of RhIG (300mcg), assuming that the fetal blood volume is less than 30 mls prior to 20 weeks. However, in the case of trauma to the mother, the doctors often want a KB stain. I have not been able to find any reference that states it is of no value to do before XX weeks gestation. I assume there is one, where even if the fetus was exsanguinated, you would be unlikely to detect it in the mother's blood. Any thoughts? Thanks, Linda