Detection of Fetal Sex in the Peripheral Blood of Pregnant Women

Abstract

Objective: To choose the best method to examine fetal sex in maternal blood as early as possible and evaluate the quantitative change of fetal-free DNA in maternal plasma. Method: One hundred and fifty pregnant women were studied at 5–9 completed weeks of gestation. Fetal cells were isolated using lymphocyte separation liquid and 3% gelatin. Furthermore, fluorescence in situ hybridization was used to examine the terminal of the Y chromosome. Nested polymerase chain reaction (PCR) and real-time fluorescence quantitative PCR (FQ-PCR) were used to amplify the SRY gene of the plasma DNA extracted from the same 150 samples of maternal blood. Sequential analysis was performed using FQ-PCR during the whole pregnancy on 32 pregnant women carrying male fetuses. Results: Using fluorescence in situ hybridization, we can find male fetal cells in maternal blood as early as the 49th day. We can also find free fetal DNA in maternal plasma as early as the 49th and the 42nd day of pregnancy using nested PCR and FQ-PCR. The amount of fetal DNA was increasing with the gestation week. The standard value of every gestation week was obtained by FQ-PCR. Conclusion: FQ-PCR was the best method to detect fetal sex in early pregnancy. There is a principle of quantitative change of free fetal DNA in maternal plasma.