Before noninvasive prenatal diagnosis on the fetal Rhesus D status (NIPD RhD) can be implemented on a mass-scale, it is crucial to define requirements regarding sample transport. The aim of this study was to determine the relation between the transport time of samples for NIPD and the concentration of fetal DNA in maternal plasma.
We analyzed qualitative and quantitative data obtained in a previous study performed with real-time PCR to determine the accuracy of NIPD RhD following two different DNA extraction protocols. The number of days from phlebotomy until freezing of plasma at the study site was recorded and defined as transport time.
NIPD RhD results of 972 specimens were analyzed according to transport time, which varied from a few hours to a maximum of 8 days (median 2 days). No decrease of cell-free fetal DNA was observed in samples with less than 6 days transport time. There was a pivotal trend to higher cycle threshold values in samples with ≥ 6 days transport time compared with those with ≤ 5 days.
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. Copyright © 2011 John Wiley & Sons, Ltd.