High sensitivity of fetal DNA in plasma compared to serum and nucleated cells using unnested PCR in maternal blood

DNA analysis of blood is conventionally performed on cells - plasma and ser um are discarded. Free DNA has been demonstrated in serum in cancer and aut oimmune disorders and in pregnancy. We investigated possible noninvasive pr enatal diagnosis using fetal DNA from maternal plasma and serum in pregnanc y. Fetal gender was determined by PCR on DNA from maternal venous blood, se rum and plasma of 65 women by boiling with or without phenol/chloroform ext raction. When sensitivities were compared for plasma, additional phenol/chl oroform extraction proved more sensitive than boiling alone (89 vs. 50%), t he observed difference was 50% (CI 19 to 81%). Extracted plasma amplified b etter than extracted serum (89 vs, 46%), the observed difference being 44% (CI 22 to 66%). In contrast, fetal gender could not reliably be determined from DNA extracted from maternal nucleated blood cells. The size of plasma and serum DNA at 15-17 weeks of gestation was >1,500 bp. This work confirms the presence of fetal DNA in maternal plasma and serum which may be applic able to noninvasive prenatal diagnosis of paternally derived DNA sequences. We conclude that optimal sensitivity requires two methods of DNA extractio n and that the use of plasma is preferred to that of serum, Copyright (C) 2 000 S. Karger AG, Basel.