Lack of Dramatic Enrichment of Fetal DNA in Maternal Plasma by Formaldehyde Treatment

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Abstract
The discovery of fetal DNA in maternal plasma has opened up new possibilities for noninvasive prenatal diagnosis (1)(2)(3)(4)(5)(6). A recent report(7) indicated that the proportion of fetal DNA in maternal plasma can be dramatically enriched through the adoption of a blood-processing protocol involving the addition of formaldehyde to maternal blood samples. Dhallan et al. (7) suggested that these observations might be the result of several factors, including a reduction in background maternal DNA by minimization of maternal cell lysis through formaldehyde-mediated cell membrane stabilization and the use of a gentle centrifugation protocol, as well as the preservation of fetal DNA through nuclease inhibition by formaldehyde. In view of the profound implications of the study (7), we aimed to validate and investigate the underlying mechanisms of the reported phenomenon. To assess the effects of several contributory factors, our study was conducted in three successive stages. In the first part of the study, we aimed to verify the effects of the previously published protocol (7) on total DNA concentrations in plasma from nonpregnant individuals. In the second part of the study, we evaluated the effects of formaldehyde addition on total and fetal DNA concentrations in maternal plasma in relation to the time of blood processing (0, 6, and 24 h after blood collection). In the last part of the study, we investigated whether the reported enrichment in circulating fetal DNA concentrations (7) might be a consequence of the imprecision of the analytical method chosen by the authors. All participants were recruited with informed consent from the Prince of Wales Hospital, Hong Kong, with institutional ethics approval. In the first part of the study, blood (24 mL) was collected into 3-mL EDTA tubes from each of eight nonpregnant volunteers and divided into …