Effect of formaldehyde treatment on the recovery of cell-free fetal DNA from maternal plasma at different processing times

Background: The effect of formaldehyde treatment on the recovery of fetal DNA from maternal plasma is controversial. We evaluated the effect of formaldehyde and investigate the underlying mechanism. Methods: Blood samples from pregnant women were treated or not treated with formaldehyde, and processed at different times. Total and fetal DNA in plasma was quantified by real-time polymerase chain reaction. Death and lysis of blood cells were assayed by trypan blue exclusion test. Plasma DNase activity was determined by the radial enzyme-diffusion method. Results: Formaldehyde addition showed no effect on the percentage of fetal DNA in samples processed 6 h after blood collection. In samples processed at 36 h, formaldehyde addition inhibited blood cell lysis and nuclease-mediated DNA degradation, thus markedly decreasing the concentration of total DNA and increasing the recovery of fetal DNA. The median (interquartile range) percentage of fetal DNA increased from 4.6% (3.8-6.8%) to 13.1% (10.3-17.0%). Conclusion: The effect of formaldehyde on the percentage of fetal DNA in maternal plasma depends on processing time and is associated with prevention of cell lysis and inhibition of plasma DNase activity. (C) 2008 Elsevier B.V. All rights reserved.