Rh sensitization after genetic amniocentesis

A retrospective evaluation was undertaken of 78 Rh-negative women who underwent genetic amniocentesis without Rh-immune globulin prophylaxis. Of the 56 patients at risk for sensitization, 3 (5.4%) became sensitized during the pregnancy in which amniocentesis was performed. This number is not statistically different from the 2.1% incidence of spontaneous Rh immunization during pregnancy. However, a trend toward increasing sensitization after second-trimester amniocentesis was noted. As the fetoplacental blood volume at 16 weeks' gestation is approximately 12 to 13 ml, a 150-micrograms dose of Rh-immune globulin is recommended for the Rh-negative patient who is undergoing genetic amniocentesis.