[First trimester fetal sex determination in maternal serum using real-time PCR]

Detection of cell-free fetal DNA in maternal urine

OBJECTIVE

To evaluate the presence of cell-free fetal DNA signals in maternal urine as a potential source of material for non-invasive prenatal diagnosis.

STUDY DESIGN

Patients referred to the regional fetal medicine unit who underwent prenatal diagnosis by chorionic villus sampling (CVS) were asked to give blood and urine immediately before the procedure. Maternal blood and urine were centrifuged at 10,000 g for 10 min. Plasma (1 mL) and urine (1 mL) supernatant were transferred to a clean tube and centrifuged again. The plasma (0.8 mL) and urine (0.8 mL) supernatant were removed without disturbing the cell pellet and stored at - 80 degrees C. Following DNA extraction, each sample was tested for the presence of Y chromosome associated DYS14 gene using real-time polymerase chain reaction (PCR). The total amount (maternal and fetal) of DNA in each sample was estimated using a quantitative real-time PCR assay.

RESULTS

Twenty patients were enrolled in the study. CVS was performed at a median gestational age of 13 weeks (range 11 + 5 - 14 + 1). There were 12 male and 8 female fetuses, as confirmed by karyotype. Y chromosome DNA was not detected in any of the 20 samples of maternal urine, including 12 of the 20 samples in which Y chromosome DNA was detected in maternal plasma (all of whom were subsequently confirmed to be carrying a male fetus). There was considerable variation in the amount of total free DNA detected in maternal urine.

CONCLUSIONS

Cell-free fetal DNA either was not present or did not amplify in maternal urine.

[Contribution of genotyping for fetal sex determination in maternal serum for preimplantation genetic diagnosis of X-linked diseases]

OBJECTIVE

Couples with a risk of transmitting X-linked diseases included in a preimplantation genetic diagnosis (PGD) center need early and rapid fetal sex determination during pregnancy in two situations. The first situation corresponds to control of embryo sexing after PGD, the second one being that of couples in PGD program having a spontaneous pregnancy. Determination of fetal sex can be achieved by karyotyping using invasive procedures such as chorionic villus sampling (CVS), amniocentesis or cordocentesis and by non-invasive procedures such as ultrasound (US) examination. CVS is the earliest invasive procedure for fetal sex determination and molecular analysis of X-linked genetic disorders during the first trimester but it is associated with a risk of fetal loss. US allows reliable fetal sex determination only during the second trimester. Recently, reliable non-invasive fetal sex determination was realized by using SRY gene amplification in maternal serum.

PATIENTS AND METHODS

We report the prospective use of fetal sex determination in maternal serum in our PGD center. Management of pregnancies was performed using this non-invasive procedure in four cases of embryo sexing control and nine cases of spontaneous pregnancies in couples included in PGD program for X-linked diseases.

RESULTS

Fetal sex results using SRY gene amplification on maternal serum were in complete concordance with fetal sex observed by cytogenetic analysis or US examination, as well as at birth.

DISCUSSION AND CONCLUSION

This new strategy allowed rapid sex determination during the first trimester and permitted to avoid performing invasive procedures in nine pregnancies.