The incidence and outcome of clinically significant antibodies detected in Rhesus-D positive pregnant women of the Northern Territory

Background: Haemolytic disease of the fetus/newborn secondary to clinically significant non-Rhesus-D antibodies has risen in importance since the advent of immunoprophylactic anti-D administration to Rhesus-D negative women. Of interest is the incidence of these antibodies in Rhesus-D positive women, who receive less frequent antenatal alloantibody screening. This is of particular concern if the antibodies arise late in pregnancy and may go undetected. Aims: To assess the proportion of Rhesus-D positive pregnant women with late developing clinically significant antibodies for haemolytic disease of the fetus/newborn, and whether these resulted in adverse fetal outcomes. Materials and Methods: A retrospective analysis over a 12-month period at a tertiary hospital in the Northern Territory. Group and antibody screen results in addition to clinical data regarding pregnancy/newborn were collected. Results: Sixty-four of 2612 women (2.5%) had red blood cell antibodies detected during their pregnancy. Of these, 21 clinically significant antibodies were detected in 19 women (0.7% of initial cohort). The most common antibody detected was anti-c (28.5%). In six of these women (0.23% of initial cohort), the antibodies were late developing. Mild jaundice was noted in three newborns with phototherapy required in one. Conclusions: Although clinically significant antibodies were detected during pregnancy, and in a small proportion of cases as a late developing antibody undetected in the first trimester screening, clinical outcomes for the newborn were mild. As such, the cost of retesting all Rhesus-D positive pregnant women in the third trimester would be considerable and unlikely to result in any meaningful clinical benefit.