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December 15, 2004

Free Fetal DNA in Maternal Circulation—Reply

Author Affiliations

Letters Section Editor: Robert M. Golub, MD, Senior Editor.

JAMA. 2004;292(23):2835-2836. doi:10.1001/jama.292.23.2835-b

In Reply: Dr Lo and colleagues suggest that a serial dilution method will have a wider confidence interval for the measured percentage of free fetal DNA compared to real-time PCR, which will increase the likelihood of inflating the effect of the formaldehyde treatment. However, for each of our samples the same serial dilution method was used to measure total DNA and fetal DNA. Any sampling variation would have affected both total DNA and fetal DNA; thus, there is no basis to presume this would result in a higher percentage of fetal DNA than actually exists. Regarding comparison with real-time PCR, we also note that Dr Lo and colleagues used serial dilutions to generate a standard curve that was used to extrapolate the amount of DNA in each sample in their real-time PCR assays.1

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