This prospective clinical trial revealed that routine determination of the fetal D status from maternal plasma is feasible. Noninvasive fetal RHD genotyping can be considered as sensitive as the traditional postnatal serologic assay.

As twin-to-twin delivery time interval seems to be an independent risk factor for adverse short-term outcome of the second twin, it should be kept short.

Because only a few laboratories offer an NIPD RhD service, we suggest a maximal transport time of 5 days from phlebotomy until freezing at the testing laboratory.