To the Editor.
—Chavez et al1 found the estimated incidence rate of Rh hemolytic disease of the newborn to be 10.6 per 10 000 total births. They also calculate the minimum achievable incidence rates of Rh disease in the United States to be 3.1 per 10 000 total births. Based on these estimates we appear to be far from the achievable minimum, presumably due to failures to use antenatal and postpartum Rh(D) immune globulin (RhIg).An alternate explanation is that the failure rate of combined antenatal and postpartum use of RhIg that the authors took from the data and method of Bowman and Pollock may be incorrect. The studies from which these data were derived used "controls" that were neither contemporary nor matched. Other studies have found failure rates of antenatal and postpartum RhIg to be as high as 0.4% for primiparous patients and 0.85% for multiparous patients.2