Hemolytic Disease of the Newborn: Lowest Achievable Incidence Rates-Reply

In Reply.  —Dr Hensleigh expresses legitimate concerns about the validity or the failure rates of RhIG, rates from which we derived our estimate for the minimum achievable incidence rates of Rh hemolytic disease. The failure rates that we used are based on the results of several studies from around the world that were conducted on populations demographically different from the population of the United States and by different methodologies. Nevertheless, the data summarized in Davey's¹ review of the McMaster Rh Conference of 1979, a more recent review by Keith et al,² and the Nova Scotia trials by Baskett et al³ suggest that for antenatal and postnatal prophylaxis combined, an overall failure estimate of 0.20% of preventing women with at-risk pregnancies from becoming Rh sensitized is a reasonable estimate.The additional contribution to overall failure rates made by women already so sensitized when they were being considered for