Non-invasive fetal sex determination using real-time PCR

Objective.?The aim of this study was to evaluate the specificity and sensitivity of the real-time quantitative PCR method for fetal gender determination in early pregnancy.

Methods.?Blood samples were collected from 46 pregnant women prior to amniocentesis. DNA was extracted from maternal plasma using a QIAmp DNA Blood Mini Kit. DNA samples were subjected to real-time quantitative PCR amplification of SRY (as a fetus-specific marker) and β-globin (as a marker for total plasma DNA) genes.

Results.?The β-globin gene sequence was detected in all samples. The SRY gene was detected in 25 of 28 plasma samples from women with male fetuses and in none of the 18 samples from women with female fetuses (sensitivity 89.2% and specificity 100%). The fetal gender was correctly determined in 43 (93.5%) of 46 maternal plasma samples. The concentration of the β-globin gene ranged from 161 to 25 568 genome-equivalents (GE)/mL (median 1051.1), while the concentration of the SRY gene ranged from 5 to 166 GE/mL (median 27.4). The percentage of free fetal DNA ranged from 0.1% to 46.1% (median 2.0%).

Conclusion.?Amplification of fetal DNA from maternal plasma by real-time quantitative PCR is a promising method for fetal sex determination in early pregnancy. However, further studies are necessary before this procedure can be included into a clinical routine.     

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

Fetal sex prediction can be achieved using PCR targeted at the SRY gene by analysing cell-free fetal DNA in maternal serum. Unfortunately, the results reported to date show a lack of sensitivity, especially during the first trimester of pregnancy. Therefore, determination of fetal sex by maternal serum analysis could not replace karyotype analysis following chorionic villus sampling. A new highly sensitive real-time PCR was developed to detect an SRY gene sequence in maternal serum. Analysis was performed on 121 pregnant women during the first trimester of pregnancy (mean gestational age: 11.8 weeks). Among them, 51 had at least one previous male-bearing pregnancy. Results were compared with fetal sex. SRY PCR analysis of maternal serum was in complete concordance with fetal sex. Among the 121 pregnant women, 61 were bearing a male fetus and 60 a female fetus. No false-negative results were observed. Furthermore, no false-positive results occurred, even though 27 women carrying a female fetus during the current pregnancy had at least one previous male-bearing pregnancy. This study demonstrates that a reliable, non-invasive sex determination can be achieved by PCR analysis of maternal serum during the first trimester of pregnancy. This non-invasive approach for fetal sex prediction should have great implications in the management of pregnant women who are carriers of an X-linked genetic disorder. Prenatal diagnosis might thus be performed for male fetuses only, avoiding invasive procedures and the risk of the loss of female fetuses.     

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

OBJECTIVE: Fetal sex prediction can be achieved using PCR targeted at the SRY gene by analyzing cell-free fetal DNA in maternal serum. Unfortunately, the results reported to date, show lack of sensitivity, especially in the first trimester of pregnancy. Therefore, determination of fetal sex by maternal serum analysis can not replace caryotype analysis following chorionic villus sampling. PATIENTS AND METHODS: A new highly sensitive real-time PCR was developed to detect a SRY gene sequence in maternal serum. Analysis was performed on 121 pregnant women during their first trimester of pregnancy (mean gestational age: 11.8 weeks). Among them, 61 had at least one previous male-bearing pregnancy. Results were compared to fetal sex. RESULTS: SRY PCR analysis of maternal serum was in complete concordance with fetal sex. Among the 121 pregnant women, 61 were bearing a male fetus and 60 a female fetus No false negative results were observed. Furthermore, no false positive results results occurred although 27 women carried female fetus during the current pregnancy, had at least one previous male-bearing pregnancy. DISCUSSION AND CONCLUSION: This study demonstrates that a reliable, non-invasive sex determination can be achieved by PCR analysis of maternal serum during the first trimester of pregnancy. This non-invasive approach for fetal sex prediction should have great implications in the management of pregnant women carriers of an X-linked genetic disorder. Prenatal diagnosis is thus performed for male fetuses only, avoiding invasive procedures and the risk of fetal loss for female fetuses.     

Non-invasive fetal sex determination on fetal erythroblasts from the maternal circulation using fluorescence in situ hybridisation

OBJECTIVE: The main purpose of this study was to evaluate the potential of a non-invasive method for fetal sex determination in clinical practice using dual-colour fluorescence in situ hybridisation (FISH) analysis. We evaluated the differences in nucleated red blood cell (NRBC) recovery from the maternal circulation using various slide preparation procedures following high-gradient magnetic cell separation (double MACS). METHODS: NRBCs were enriched from peripheral blood mononuclear cells of 63 pregnant women between 12 and 37 weeks of gestation by double MACS involving simultaneous CD14+ and CD45+ maternal cell depletion and CD71+ fetal cell enrichment. Isolated cells were analysed by dual-colour FISH with X- and Y-specific probes. Before applying the FISH technique, cells were treated using three different protocols. Cells were either fixed in methanol:acetic acid (3:1) and dropped immediately onto glass slides (protocol 1) or treated with 75 mM KCl before resuspension in fixative (protocol 2). Alternatively, isolated cells were transferred onto glass slides and then treated using a method described in the literature (protocol 3). RESULTS: Using various slide preparation procedures, fixed cell numbers as well as the quality of slides differed significantly. Using protocol 1, fetal sex was well determined in 30 cases, in 15 out of 17 male fetuses (1-13, mean 3 fetal cells were found among 5-164, mean 50 maternal cells) and in 15 female fetuses (7-178, mean 56 fixed cells). On the other hand, interpretation difficulties occurred in 7 out of 8 studied cases using protocol 2 due to a lack of cells or damage to the isolated cells. The highest recovery of fixed cells was achieved using protocol 3 (27-411, mean 186); fetal cells positive for the Y signal (2-12, mean 6) were detectable in all studied cases (n = 16). In 7 of the samples from women carrying female fetuses, we could only detect cells with two X signals (51-182, mean 103). All of the experiments were interpretable due to the presence of compact cells with well-visible red and green signals. CONCLUSION: Our study revealed that using protocol 3 as the post-MACS treatment results in improved NRBC recovery and enables a reliable prospective non-invasive fetal sex determination.     

Non-invasive fetal RHD exon 7 and exon 10 genotyping using real-time PCR testing of fetal DNA in maternal plasma

OBJECTIVE: In this prospective study, we assessed the feasibility of foetal RHD genotyping by analysis of DNA extracted from plasma samples of Rhesus (Rh) D-negative pregnant women using real-time PCR and primers and probes targeted toward exon 7 and 10 of RHD gene. METHODS: We analysed 24 RhD-negative pregnant woman and 4 patients with weak D phenotypes at a gestational age ranging from 11th to 38th week of gestation and correlated the results with serological analysis of cord blood after the delivery. RESULTS: Non-invasive prenatal foetal RHD exon 7 genotyping analyses of maternal plasma samples was in complete concordance with the serological analysis of cord blood in all 24 RhD-negative pregnant women delivering 12 RhD-positive and 12 RhD-negative newborns. RHD exon-10-specific PCR amplicons were not detected in 2 out of 12 studied plasma samples from women bearing RhD-positive foetus, despite the positive amplification in RHD exon 7 region observed in all cases. In 1 case red cell serology of cord blood revealed that the mother had D-C-E-c+e+ C(w)- and the infant D+C-E-c+e+ C(w)+ phenotypes. RhD exon 10 real-time PCR analysis of cord blood was also negative. These findings may reflect that DC(w)- paternally inherited haplotype probably possesses no RHD exon 10. In another case no cord blood sample has been available for additional studies. The specificity of both RHD exon 7 and 10 systems approached 100% since no RhD-positive signals were detected in women currently pregnant with RhD-negative foetus (n = 8). Using real-time PCR and DNA isolated from maternal plasma, we easily differentiated pregnant woman whose RBCs had a weak D phenotype (n = 4) from truly RhD-negative patients since the threshold cycle (C(T)) for RHD exon 10 or 7 amplicons reached nearly the same value like C(T) for control beta-globin gene amplicons detecting the total DNA present in maternal plasma. However in these cases foetal RhD status cannot be determined. CONCLUSION: Prediction offoetal RhD status from maternal plasma is highly accurate and enables implementation into clinical routine. We suggest that safe non-invasive prenatal foetal RHD genotyping using maternal plasma should involve the amplification of at least two RHD-specific products.     

Replicate real-time PCR testing of DNA in maternal plasma increases the sensitivity of non-invasive fetal sex determination

BACKGROUND: We determined fetal sex in pregnancies referred for invasive prenatal diagnosis procedures by analysis of DNA in maternal plasma. METHODS: Twelve pregnancies at risk of X-linked haemophilia and 32 pregnancies at risk of chromosomal aneuploidies at a gestational age ranging from 10 to 18 weeks recruited before chorionic villus sampling or amniocentesis were involved in the study. Male fetal DNA in maternal plasma was detected by using real-time polymerase chain reaction with the SRY gene as a marker. RESULTS: The specificity of the system reached 100% (no Y signal was detected in 17 women pregnant with a female fetus) and the sensitivity reached 100% (SRY amplification in 27 examined samples). CONCLUSIONS: Amplification of free fetal DNA in maternal plasma is a valid and rapid technique for predicting fetal sex in first- and second-trimester pregnancies and could allow the restriction of invasive sampling procedures to male fetuses at risk of X-linked disorders.     

Non-invasive fetal sex determination by maternal plasma sequencing and application in X-linked disorder counseling

Abstract

Objective: To develop a fetal sex determination method based on maternal plasma sequencing (MPS), assess its performance and potential use in X-linked disorder counseling.

Methods: 900 cases of MPS data from a previous study were reviewed, in which 100 and 800 cases were used as training and validation set, respectively. The percentage of uniquely mapped sequencing reads on Y chromosome was calculated and used to classify male and female cases. Eight pregnant women who are carriers of Duchenne muscular dystrophy (DMD) mutations were recruited, whose plasma were subjected to multiplex sequencing and fetal sex determination analysis.

Results: In the training set, a sensitivity of 96% and false positive rate of 0% for male cases detection were reached in our method. The blinded validation results showed 421 in 423 male cases and 374 in 377 female cases were successfully identified, revealing sensitivity and specificity of 99.53% and 99.20% for fetal sex determination, at as early as 12 gestational weeks. Fetal sex for all eight DMD genetic counseling cases were correctly identified, which were confirmed by amniocentesis.

Conclusions: Based on MPS, high accuracy of non-invasive fetal sex determination can be achieved. This method can potentially be used for prenatal genetic counseling.     

Noninvasive determination of fetal RhD status using fetal DNA in maternal serum and PCR

OBJECTIVE: Because prenatal testing of fetal RhD status by amniocentesis carries small yet finite risks to the fetus and mother, this study sought to determine whether fetal DNA in maternal serum could be used to detect fetal RhD status by polymerase chain reaction (PCR). METHODS: A retrospective analysis was made of frozen serum specimens from 20 sensitized RhD-negative pregnant women (ranging from 15.0 to 36.0 weeks' gestation) who were confirmed by serology at birth to have been carrying RhD-positive fetuses. Eleven serum specimens from RhD-negative individuals served as controls. DNA was isolated from serum and used in two PCR-based methods to detect a 99 base pair (bp) DNA fragment specific for the RhD gene and a 113 bp fragment specific for the RhCE gene as control. RESULTS: Overall, in 14 (70%) of 20 RhD-positive fetuses the 99 base pair RhD-specific PCR product was detected. There was no false positive detection among the 11 control serum specimens. CONCLUSION: The results illustrate the ability to detect fetal RhD sequences in maternal serum of sensitized women. Moreover, the findings demonstrate that fetal single-gene disorders can be detected prenatally by using DNA isolated only from maternal serum.     

Early-second-trimester fetal sex determination with ultrasound

A prospective investigation was performed to determine the accuracy of fetal gender determination with ultrasound at 13-19 weeks' gestation. A determination could be made in 91 of 100 women. Factors associated with nonvisualization were maternal obesity and breech presentation. The findings on ultrasound were compared with phenotypic sex after birth. The overall accuracy of sex prediction was 92.3%; for males it was 89.5% and for females, 97.1%. Significantly fewer errors were noted as experience with gender identification increased.     

利用PRINS技术进行无创性产前诊断胎儿非整倍体

目的利用引物原位合成术(primedin situ labelling,PRINS)进行产前诊断胎儿非整倍体,探索无创性产前诊断的可靠便捷的新方法。方法采用流式细胞术从120例孕妇外周血中分离出胎儿有核红细胞,应用PRINS技术分别检测胎儿有核红细胞内的X、Y及21号染色体。结果120例标本中每例都可以检测出X染色体,敏感性和特异性均为100%;检测出Y染色体69例,敏感性92%(69/75),特异性为100%(69/69),检测出Klinefelter(XXY)综合征1例,唐氏综合征2例。结论应用PRINS技术对孕妇外周血中的胎儿细胞进行无创性产前诊断胎儿非整倍体是一种快速、敏感性高、特异性强的新方法,具有应用于临床的前景与价值。     

Non-invasive diagnosis of fetal sex; utilisation of free fetal DNA in maternal plasma and ultrasound

Non-invasive prenatal diagnosis is now a clinical reality, using both early ultrasound and molecular DNA methods. Technical advances in the sensitivity of the polymerase chain reaction (PCR), coupled with the finding that significant levels of fetal DNA (ffDNA) are found in maternal plasma and serum, has enabled the ready detection of paternally inherited genes or polymorphisms. Routine maternal plasma-based genotyping is now available for the determination of fetal sex and RHD blood group status (Van der Schoot et al., 2003). This review touches briefly on the ultrasound diagnoses and then focuses on the application of free ffDNA for fetal sex determination, indicating the Y-chromosome targets exploited in this strategy and the merits of their utilisation.     

Non-invasive prenatal screening of fetal sex chromosomal abnormalities: perspective of pregnant women

Objective: To study whether pregnant women would like to be informed if sex chromosomal abnormalities (SCA) were suspected with the non-invasive prenatal diagnosis of fetal Down syndrome (the NIFTY) test. Methods: Two hundred and one patients carried a singleton pregnancy requesting the NIFTY test were invited to give their preferences if there was suspicion of SCA by the NIFTY test. Results: Over 93.5% were ethnic Chinese, with a mean age of 36. Prior Down screening was positive in 66 (32.8%). Over 50% of subjects considered SCA to be better in terms of disability compared to Down syndrome, and only 5.2% considered SCA to be worse. Yet, the majority (198, 98.5%) indicated that they wanted to be informed if there was suspicion of SCA. Of whom 34.8% would have an amniocentesis for confirmation, while 57.1% were not certain, indicating the possibility of accepting these conditions. Conclusion: Besides screening Down syndrome by NIFTY, most pregnant women would also like to be informed if there was suspicion of SCA. Those screened positive should be counseled by those with experience in genetics to avoid unnecessary pregnancy termination.     

Rapid determination of fetal sex using amniotic fluid cells and the polymerase chain reaction

Summary We determined the sex of 50 fetuses by an amplification of the Y-chromosome specific fragment using the polymerase chain reaction (PCR). Amniotic fluid cells were collected by amniocentesis from pregnant women at 14 to 17 weeks of gestation. Total DNA was purified from cells in 1 ml of amniotic fluid. When only the expected 130 base pair X-chromosome specific fragment was detected, we identified the fetus as female, while when both the expected 170 base pair Y-chromosome specific and X-chromosome specific fragments were detected, we identified it as male. In all cases, identification was confirmed either by chromosome analysis or post partum.     

Prenatal sex determination using ultrasound

The fetal urogenital region could be visualized by single routine sonography after the 20th gestational week in 66.4 per cent, after the 24th one in 74.4 per cent (n = 1002). Compared with the true sex of 875 children after birth 90.2 per cent of the girls and 75.9 per cent of the boys were determined correctly during pregnancy. The prenatal prognosis of a boy was confirmed in 90.3 per cent, of a girl only in 75.7 per cent. Multiple examinations make raise perceptibility and certainty. These differences and possible consequences in practice are discussed. In twin pregnancies final statements could not be afforded because of the more difficult conditions.     

Direct quantification of fetal cells in maternal blood by real-time PCR

BACKGROUND: Fetal cells in maternal blood still present an enticing alternative for the development of a safe and efficacious non-invasive method for prenatal diagnosis. However, most enrichment methods are very tedious and have failed to realise this long sought after goal. We developed a simple, robust TaqMan real-time PCR assay to directly quantify male fetal cells in maternal blood using the multi-copy DYS14, without the need for any additional enrichment procedure. METHODS: The sensitivity of the DYS14 assay was evaluated by using female genomic DNA spiked with male DNA or male cells. The specificity of the DYS14 assay was evaluated by examining 40 adult blood samples and 44 maternal blood samples from pregnant women with known fetal gender. Direct quantification of fetal cells in maternal blood was performed in 14 of the maternal blood samples by the DYS14 assay. The results were compared to those by SRY assay. RESULTS: The sensitivity of DYS14 PCR assay was found to be higher than that of SRY assay for the detection of fetal cells. The number of fetal cells in maternal blood did not exceed 2/mL blood. The presence of cell-free fetal DNA in maternal blood could lead to erroneous quantification of fetal cell DNA. The number of fetal cells detected in blood cell pellets, which had been unwashed to remove the cell-free fetal DNA, was indeed significantly higher than those in extensively washed samples. CONCLUSIONS: We quantified the fetal cells in maternal blood without fetal cell enrichment procedures by TaqMan real-time PCR for a multi-copy DYS14 locus. Our assay is sensitive and also suitable for automation, and may be a useful tool for the determination of fetal-maternal cell trafficking, such as microchimerism.     

Implications of incorrect determination of fetal sex by ultrasound

Objective: To assess the experiences of women following incorrect determination of fetal sex by ultrasound. Method: A 3-year prospective cohort study of 102 women with discordance between fetal sex determined by ultrasound scan and birth sex. Participants were interviewed using 2 structured pretested questionnaires. The first questionnaire was undertaken within 24 h of delivery. The women were followed up with a second questionnaire 6–9 months later. In-depth interviews were also carried out at this time. Results: Women who had received an incorrect determination of fetal sex by ultrasound experienced marital conflicts, domestic violence, negative perceptions of ultrasound, and a desire for reversal of tubal ligation. Conclusion: Incorrect determination of fetal sex by ultrasound has implications that can affect the mental and psychological health of the mother and the upbringing of the newborn.     

Quantitative analysis of intact fetal cells in maternal plasma by real-time PCR

OBJECTIVE: Fetal genetic materials in maternal circulation might be potentially used for non-invasive prenatal diagnosis (NIPD). In this study, we quantitatively analysed the intact fetal cells existing in maternal plasma, which would be a special method of NIPD. STUDY DESIGN: Eleven samples from preeclamptic patients, two samples from patients with RhD incompatibilities, and 30 samples from normal pregnancies as controls were collected. The intact cells in the plasma fraction were separated by centrifugation at high speed. The intact cell pellets were washed with PBS to remove any cell-free DNA. RESULTS: We were able to detect intact fetal cells in 3 out of 11 preeclamptic plasma samples from women carrying male fetuses, and from both plasma samples of RhD incompatibility affected pregnancies. However, intact fetal cells were not detected in all the 16 normal pregnancies with a male fetus, although cell-free fetal DNA was detected in all these cases. CONCLUSIONS: Intact fetal cells might be present in maternal plasma. However, the rarity of these cells limits their use for reliable, non-invasive prenatal diagnosis. The detection of such cells was successful in some preeclamptic and RhD incompatibility samples, not in the normal controls. Therefore, as opposed to free fetal DNA in maternal blood the use of intact fetal cells does not provide a reliable mode for NIPD.