Fetal DNA testing may eliminate need for anti-RhD immunoglobulin

Using high throughput RHD genotyping of fetuses may obviate the need for anti-RhD immunoglobulin in RhD-negative pregnant women, according to research published April 3 in BMJ Online First.

Kirstin Finning, and colleagues at NHS Blood and Transplant in Bristol, U.K., took blood samples from 1,997 RhD-negative pregnant women on or before 28 weeks' gestation. They established the accuracy of detecting fetal RHD genotyping using fetal DNA in maternal plasma by comparing it with the RhD phenotype determined serologically using cord blood.

Out of the 1,869 cord blood samples, in 1,788 cases (95.7 %), genotyping was accurately predicted using fetal DNA in maternal plasma. In 64 cases (3.4%), results were either inconclusive or unobtainable, 14 samples (0.8%) yielded a false-positive result and three (0.2%) yielded a false-negative result.

"If these results had been applied as a guide to treatment, only 2% of the women would have received anti-RhD unnecessarily, compared to 38% without the genotyping," the authors write. "Clearly there could be benefits from taking maternal blood samples for fetal RHD genotyping at earlier stages of the pregnancy than 28 weeks' gestation to coincide with existing planned antenatal visits," they add.

Finning K, Martin P, Summers J, et al. Effect of high throughput RHD typing of fetal DNA in maternal plasma on use of anti-RhD immunoglobulin in RhD negative pregnant women: prospective feasibility study. BMJ. 2008;336:816-818. doi:10.1136/bmj.39518.463206.25..