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.     

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.     

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.     

荧光定量PCR检测孕妇血浆中胎儿DNA的研究

目的探讨荧光定量PCR（fluorescence quantitative PCR，FQ-PCR）方法检测孕妇血浆中胎儿DNA的可行性，探讨胎儿DNA在孕妇血浆中的含量及其在孕期的变化规律。方法以胎儿SRY基因序列作为胎儿DNA在孕妇血浆中的标志，应用荧光MGB（Minor Groove Binder）探针实时定量PCR方法连续测定30例孕妇在不同孕期和产后共237份血浆标本中胎儿DNA的含量。结果使用该方法最低可检测到20000个女性DNA中的一个男性DNA。孕妇血浆中最早检出SRY序列的时间为孕6^＋6周。孕8周起，所有怀男胎孕妇的标本中均可检出SRY序列，其含量随着妊娠的进展而增高，在晚期妊娠达高峰，产后24～48h血浆中SRY序列检测均为阴性。胎儿DNA在孕妇血浆总DNA含量中的相对浓度分别为孕早期4．88％、孕中期6．10％、孕晚期4．77％。全部实验无假阳性和假阴性出现。结论FQ-PCR方法是一种灵敏度和准确性高，特异性强的定量检测孕妇血浆中胎儿游离DNA的方法，孕妇血浆中存在高浓度的胎儿DNA，可用于无创伤性产前基因诊断。     

Quantitative analysis of DNA levels in maternal plasma in normal and Down syndrome pregnancies

BACKGROUND: We investigated fetal and total DNA levels in maternal plasma in patients bearing fetuses affected with Down syndrome in comparison to controls carrying fetuses with normal karyotype. METHODS: DNA levels in maternal plasma were measured using real-time quantitative PCR using SRY and beta-globin genes as markers. Twenty-one pregnant women with a singleton fetus at a gestational age ranging from 15 to 19 weeks recruited before amniocentesis (carried out for reasons including material serum screening and advanced material age), and 16 pregnant women bearing fetuses affected with Down syndrome between 17 to 22 weeks of gestation were involved in the study. RESULTS: The specificity of the system reaches 100% (no Y signal was detected in 14 women pregnant with female fetuses) and the sensitivity 91.7% (SRY amplification in 22 of 24 examined samples). The median fetal DNA levels in women carrying Down syndrome (n=11) and the controls (n=13) were 23.3 (range 0-58.5) genome-equivalents/ml and 24.5 (range 0-47.5) genome-equivalents/ml of maternal plasma, respectively (P = 0.62). The total median DNA levels in pregnancies with Down syndrome and the controls were 10165 (range 615-65000) genome-equivalents/ml and 7330 (range 1300-36750) genome-equivalents/ml, respectively (P = 0.32). The fetal DNA proportion in maternal plasma was 0%-6 % (mean 0.8%) in women carrying Down syndrome and 0%-2.6 % (mean 0.7 %) in the controls, respectively (P=0.86). CONCLUSIONS: Our study revealed no difference in fetal DNA levels and fetal DNA: maternal DNA ratio between the patients carrying Down syndrome fetuses and the controls.     

Elevated amniotic fluid leptin levels in pregnant women who are destined to develop preeclampsia

OBJECTIVE: To analyze whether leptin levels of the amniotic fluid elevate during early pregnancy in women destined to develop preeclampsia and to evaluate the relationship between amniotic fluid leptin levels and gestational age, maternal body mass index, and fetal sex. STUDY DESIGN: Leptin levels of the amniotic fluid were compared in two groups of women, preeclamptic (n = 20) and normotensive pregnant (n = 40), matched for fetal sex, maternal body mass index at sampling, gravidity and fetal gestational age at sampling. Furthermore, amniotic leptin levels in 400 normotensive pregnant women were analyzed for their correlation with gestational age, maternal body mass index, and fetal sex. RESULTS: Median leptin concentrations were significantly higher (p < 0.001) in the women with preeclampsia (7.3+/-0.7 ng/ml) than in the normotensive pregnant women (4.1 +/- 0.3 ng/ml), independent of fetal sex. The leptin levels in the amniotic fluid decreased with advanced gestational age (r = 0.24, p < 0.001). Amniotic fluid leptin levels in the pregnant women carrying a female fetus (5.6+/-0.3ng/ml) were significantly higher than those carrying a male fetus (4.7+/-0.2 ng/ml) (p = 0.004). CONCLUSION: Higher amniotic fluid leptin levels were observed in the preeclamptic pregnant women, and they decreased as gestational age advanced. Furthermore, the women with a female fetus were noted to have higher amniotic fluid leptin levels.     

Fetal sex determination from maternal plasma in pregnancies at risk for congenital adrenal hyperplasia

OBJECTIVE: To determine first-trimester fetal sex by isolating free fetal DNA from maternal plasma. METHODS: The index case was a pregnant woman who previously delivered a girl with congenital adrenal hyperplasia. The SRY gene as a marker for the fetal Y chromosome was detected in maternal serum and plasma by quantitative polymerase chain reaction analysis. Simultaneously, we performed the same test in 25 and 19 women in the first and second trimester, respectively, and compared plasma results with fetal gender as assessed by prenatal karyotyping or as seen at ultrasound or birth. RESULTS: In 44 of 45 patients at gestational ages ranging from 8 3/7 to 17 3/7 weeks, we correctly predicted fetal sex using quantitative polymerase chain reaction analysis of the SRY gene in maternal plasma. In one case, the test result was inconclusive. Overall, fetal sex was correctly predicted in 97.8% of cases (95% confidence interval 88.2%, 99.9%). CONCLUSION: Amplification of free fetal DNA in maternal plasma is a valid technique for predicting fetal sex in early pregnancy. In case of pregnancies at risk for congenital adrenal hyperplasia, the technique allows restriction of dexamethasone treatment to female fetuses resulting in a substantial decrease of unnecessary treatment and invasive diagnostic tests.     

Feasibility study of using fetal DNA in maternal plasma for non-invasive prenatal diagnosis

BACKGROUND: The discovery of the presence of fetal genetic material in maternal blood has opened up a new approach to prenatal diagnosis. One approach that has been extensively investigated over the past few decades is the isolation of fetal cells from maternal blood (Herzenberg et al. Proc Natl Acad Sci USA. 1979;76:1453-5; Bianchi et al. Proc Natl Acad Sci USA. 1990;87:3279-83; Cha et al. Prenat Diagn. 2005;25:586-91). As the fetal cells are scarce and the enrichment is of low efficiency, the technique could not be implemented in clinics. In 1997, Lo et al. (Lancet 1997;350(9076):485-7) discovered that cell-free fetal DNA is present in the plasma and serum of pregnant women. This discovery suggests that maternal plasma/serum DNA may be a useful source of material for non-invasive prenatal diagnosis. The objective of our study was to investigate the feasibility of using fetal DNA in maternal plasma for prenatal diagnosis. METHODS: Plasma DNA in 277 blood samples of 40 pregnant women at the gestational period from 5 to 40 weeks and 24 h after delivery were extracted by column separation. FQ-PCR was used to amplify the SRY sequence in 237 plasma samples of 30 pregnant women. Fluorescent PCR was used to amplify 9 short tandem repeat loci simultaneously in 40 plasma samples of 10 pregnant women, and genomic DNA samples from their husbands were amplified by the same method. RESULTS: The fetal SRY sequence could be detected from the 7th week of gestation, with a concentration that increased with progressing gestational age, attaining its highest peak before delivery. Twenty-four hours after delivery, fetal SRY sequence could not be detected in the maternal plasma. The concordance rate of the SRY sequence amplification results of plasma-free DNA, with real fetal gender was 100%. Analysis of maternal plasma samples collected during pregnancy revealed the presence of paternally inherited fetal-specific alleles. Among the 30 collected plasma samples, fetal-specific alleles were detected in 23 plasma DNA samples. The rate of positive results was 76% (23/30), and the frequency of positive results was 6/10 in early pregnancy, 8/10 in middle pregnancy, and 9/10 in late pregnancy. Short tandem repeats could not be detected from the maternal plasma 24 h after delivery. CONCLUSION: Fluorescent PCR can be used for amplification of fetal SRY sequence and STRs in maternal plasma to obtain fetal genetic information, which may have implications for non-invasive prenatal diagnosis of certain hereditary diseases.     

孕妇血浆中胎儿DNA的数量变化的研究

目的探讨孕妇血浆中胎儿游离DNA的数量变化的规律。方法提取68例孕妇血浆中的DNA,用实时荧光定量聚合酶链式反应(FQ-PCR)技术检测其胎儿SRY基因,并对其中怀男胎孕妇外周血浆中的胎儿DNA的数量进行动态分析。结果在怀男胎的孕妇外周血中均检测到了SRY基因,而在怀女胎的孕妇中未检测到。胎儿游离DNA最早出现的时间平均为7.7周,SRY基因拷贝数平均为5.53copies/ml。随孕期的增加,母血浆中胎儿DNA的含量在逐渐增加,并得出各孕周的标准参考值。在分娩后母血中胎儿DNA的含量就显著下降,到分娩后第二天就完全不能检测到。结论孕妇外周血浆中游离DNA的含量变化具有一定的规律,可以利用其进行无创伤性产前诊断。     

Detection of Y chromosome-specific DNA in the plasma and urine of pregnant women using nested polymerase chain reaction

The present study was undertaken to evaluate a nested polymerase chain reaction (PCR) for detection of Y chromosome-specific fetal DNA in maternal plasma and urine of pregnant women during different gestational stages. DNA isolated from plasma and urine samples of 80 pregnant women (between 7 and 40 weeks' gestation) underwent amplification for Y chromosome-specific 198 bp DNA by nested PCR. The postpartum analysis of fetal gender showed that 55 women carried male and 25 female fetuses. Among the 55 women bearing male fetuses, Y chromosome-specific signals were detected in 53 (96%) plasma and 21 (38%) urine samples. Moreover, out of 25 women bearing female fetuses, 3 (12%) and 1 (4%) women had Y chromosome-specific signal in plasma and urine, respectively. Analysis of results with respect to gestational age revealed that there was no significant difference in the detection of Y chromosome-specific DNA between different trimesters in maternal plasma of women bearing male fetuses. These results showed that fetus-specific DNA was detected with high sensitivity (96%) and specificity (88%) in the maternal plasma by nested PCR, and therefore the method could be useful as a non-invasive procedure for fetal sex determination and prenatal diagnosis.     

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 beta-globin (as a marker for total plasma DNA) genes. RESULTS: The beta-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 beta-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.     

The impact of fetal gender and ethnicity on the risk of spontaneous preterm delivery in women with symptoms of preterm labor

Objective: The objective of this study is to evaluate the relation among fetal gender, ethnicity, and preterm labor (PTL) and preterm delivery (PTD).

Methods: A secondary analysis was performed of a prospective cohort study including women with symptoms of PTL between 24 and 34 weeks. The proportion of women carrying a male or female fetus at the onset of PTL was calculated. Gestational age at delivery and risk of PTD of both fetal genders was compared and interaction of fetal gender and maternal ethnicity on the risk of PTD was evaluated.

Results: Of the 594 included women, 327 (55%) carried a male fetus. Median gestational age at delivery in women pregnant with a male fetus was 37 5/7 (IQR 34 4/7–39 1/7) weeks compared with 38 1/7 (IQR 36 0/7–39 5/7) weeks in women pregnant with a female fetus (p?=?0.032). The risk of PTD did not differ significantly. In Caucasians, we did find an increased risk of PTD before 37 weeks in women pregnant with a male fetus (OR 1.9 (95% CI 1.2–3.0)).

Conclusions: The majority of women with PTL are pregnant with a male fetus and these women deliver slightly earlier. Race seems to affect this disparity.     

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.     

Prenatal fetal sex diagnosis by detecting amelogenin gene in maternal plasma

OBJECTIVES: To provide a new, reliable noninvasive method for fetal sex determination. METHODS: Fetal sex was detected in 32 early pregnant women by identifying the amelogenin gene in maternal plasma using nested PCR analysis. First, the 122/128 bp of X-Y homologous region containing 6 bp deletions in the intron 3 of amelogenin gene in X chromosome was amplified, and then the nested PCR was carried out, whose 3' end of the upstream primer is just located in the deletion region. The fetus was male or female, depending on whether it had the 89-bp nested PCR product or not. RESULTS: The 89 bp of nested PCR product was detected in 19 plasma samples obtained from pregnant women, deducing they bear the male fetus and the remaining pregnant women bear female. When compared with the birth outcome, two samples were pseudo-positive. The coincidence was 93.8%. This method had high sensitivity that even trace amount of target fetal DNA (10 pg) could be detected. CONCLUSIONS: This conventional nested PCR analysis of amelogenin gene promises to be a reliable method for noninvasive fetal sex determination at early pregnancy using maternal plasma DNA.     

Culture of endothelial cells isolated from maternal blood using anti-CD105 and CD133

OBJECTIVES: We hypothesized that fetal cells in maternal blood that do not respond to hematopoietic culture conditions represent endothelial cells. We investigated whether endothelial progenitor cells of fetal origin may be selected from maternal blood on the basis of their expression of CD133 or CD105 and expanded in culture. METHODS: Peripheral blood mononuclear cells from 16 pregnant women (gestational age: 11 to 24 weeks) were labeled with magnetic beads coupled to anti-CD133 or anti-CD105. Selection of labeled cells was performed using MACS. Resulting CD133+, CD105+, and CD133-/CD105- cell fractions were placed in culture in conditions favoring endothelial cells for 7 days (positive fractions) to 30 days (depleted fractions). Cells from women carrying male fetuses were analyzed by conventional PCR (SRY primers) for detection of male cells. RESULTS: Expansion of cells isolated from all subjects occurred in each of the cell fractions. No PCR products consistent with the presence of male cells were detected in women carrying male fetuses. CONCLUSION: CD133+ and CD105+ cells isolated from maternal blood can be expanded in vitro under endothelial conditions. These cells appear to be of maternal, rather than fetal, origin.     

Fragmentation of cell-free fetal DNA in plasma and urine of pregnant women

OBJECTIVES: We assessed the effect of freezing on fragmentation of fetal DNA in maternal plasma and differences in DNA fragmentation between plasma and urine from pregnant women. METHODS: 1. We prepared seven kinds of real-time PCR assays to amplify different-sized amplicons targeting the SRY gene. Fragmentation of fetal DNA in maternal plasma was compared between new (n=10) and 4-year-old samples (n=10). 2. To investigate differences in fragmentation of fetal DNA between plasma and urine from pregnant women, we amplified three different-sized amplicons and compared DNA fragmentation between plasma and urine (n=7). RESULTS: 1. Relative concentrations of fetal DNA compared to a 63-bp amplicon in new samples were 53.1, 42.0, 9.2 and 2.0% (median) for PCR amplicons of 107, 137, 193 and 313 bp, respectively. Concentrations in 4-year-old samples were 70.4, 40.9, 11.9 and 2.3%, respectively. 2. Although fetal DNA in urine was not detected for 107- and 137-bp amplicons of the SRY sequence, fetal DNA using a 63-bp amplicon was detectable in five of seven cases (71.4%). CONCLUSION: Cell-free fetal DNA in maternal plasma is stable under cryopreservation at -20 degrees C for at least 4 years. Approximately, 60% of fetal DNA in maternal plasma was fragmented to <100-bp long, and fetal DNA in urine was further fragmented. Maternal urine may be usable for detection of fetal DNA, although smaller target size is more important for PCR amplification of fetal DNA in urine than in the analysis of plasma from pregnant women.     

Cell-free fetal DNA in the plasma of pregnant women with severe fetal growth restriction

OBJECTIVE: Although there have been reports of increased fetal nucleated erythrocytes in the blood of pregnant women who are carrying growth-restricted fetuses, there have been no reports of quantification of fetal DNA concentration in the plasma of women with fetal growth restriction. We quantified fetal DNA concentration in the plasma of pregnant women with preeclampsia and/or fetal growth restriction. STUDY DESIGN: We examined maternal plasma from 9 pregnant women with fetal growth restriction and 9 with preeclampsia and from 20 women who were gestational age-matched normal control subjects. All women carried a male fetus. DNA was extracted from 1.5-mL plasma samples, and the DYS14 and beta-globin gene were analyzed by real-time quantitative polymerase chain reaction. RESULTS: The concentration of fetal DNA was significantly higher in subjects with preeclampsia than in fetal growth restriction subjects and normal control subjects. Fetal DNA concentrations in fetal growth restriction subjects were similar to those of normal control subjects. The concentration of total DNA (beta-globin) was significantly higher in subjects with preeclampsia when compared with healthy control subjects. CONCLUSION: We demonstrated that there was no increase in fetal DNA in the plasma of pregnant women with fetal growth restriction and that most fetal DNA in maternal plasma originates from trophoblasts.     

Maternal urine for prenatal diagnosis--an analysis of cell-free fetal DNA in maternal urine and plasma in the third trimester

OBJECTIVES: The aim of the study was the detection, quantification and correlation of cell-free fetal (cff) DNA in maternal urine and plasma in normal and complicated pregnancies during the third trimester. METHODS: One hundred and fifty-one urine and plasma samples obtained from 96 women carrying male fetuses, and 55 carrying female fetuses were collected and analyzed for cff-DNA using fluorescent PCR and quantitative real-time PCR. DNA was extracted from 1 mL maternal urine and analyzed with two different primer sets (SRY and DYS-14). The concentrations of cff and total DNA in maternal plasma were correlated with maternal and obstetric parameters using appropriate correlation analyses. RESULTS: Y-chromosome-specific sequences were detected in 31 of 96 (32.3%) urine samples collected from women pregnant with male fetuses using DYS-14 and in 6 of 96 (6.3%) urine samples using SRY as primers using real-time PCR. All 96 plasma samples obtained from women carrying male fetuses were positive for cff-DNA using real-time PCR. Cff-DNA exhibited a correlation with gestational age (R = 0.244; P = 0.018) and an inverse correlation with the latency between blood collection and birth (R = - 0.218; P = 0.036). Total DNA showed a correlation with placental weight (R = 0.182; P = 0.034) and pregnancy-associated complications (R = 0.280; P < 0.001). CONCLUSION: Our data confirm that cff-DNA is cleared by the kidneys in detectable amounts, but due to its low concentration or problematic detection in maternal urine this source seems inappropriate for noninvasive prenatal diagnosis.     

SRY-specific cell free fetal DNA in maternal plasma in twin pregnancies throughout gestation

Objectives

Levels of SRY-specific cell free fetal DNA (SRY-cffDNA) in maternal plasma were investigated in twin pregnancies with two male fetuses versus one male and one female fetus and singleton male pregnancies during second and third trimester. The aim was to evaluate at which gestational age the amount of SRY-cffDNA reflects the number of fetuses and placentas respectively.

Methods

251 venous blood samples were analyzed from a total of 178 women with male or mixed-gender twin pregnancies and male singleton pregnancies in the second and the third trimester. The concentration of SRY-cffDNA was determined by quantitative real time PCR using the Y-chromosome specific SRY assay. For statistical analysis these three groups were divided into four subgroups according to their gestational age.

Results

During second trimester levels of SRY-cffDNA showed no differences between twin and singleton pregnancies. After 28 weeks SRY-cffDNA of male twin pregnancies was significantly increased compared to singleton male pregnancies and mixed-gender twin pregnancies with no differences between the latter two.

Conclusion

The level of SRY-cffDNA in maternal serum of twin pregnancies reflects the number of fetuses only during the third trimester. Hence its use as a diagnostic tool for complications related to altered SRY-cffDNA levels in twin pregnancies should be evaluated at different weeks of gestation, especially during the second trimester.     

Cell-free fetal DNA concentration in plasma of patients with abnormal uterine artery Doppler waveform and intrauterine growth restriction--a pilot study

OBJECTIVE: To evaluate if an increased amount of fetal DNA concentration can be found in women screened positive for intrauterine growth restriction because of abnormal uterine artery Doppler waveforms. METHODS: We enrolled eight pregnant women (each bearing a male fetus), with the evidence of abnormal uterine artery Doppler waveforms, and 16 control patients for a case-control study matched for gestational age (1 : 2). Uterine artery Doppler was carried out at 20 to 35 weeks' gestation (median 29). The mean uterine artery resistance index (RI) was subsequently calculated, and a value >0.6 was considered positive for the clinical features of pre-eclampsia. The SRY locus was used to determine the amount of male fetal DNA in the maternal plasma at the time of Doppler analysis. RESULTS: Two controls (normal Doppler) were excluded from the final analysis because they had a pre-term delivery. One case (abnormal Doppler) had evidence of intrauterine growth restriction at the time of enrolment. In four out of eight cases (abnormal Doppler), intrauterine growth restriction was subsequently observed. Multiples of median (MoM) conversion of the fetal DNA values showed an increase of 1.81 times in the cases when compared to the controls. An increase of 2.16 times was instead observed for the cases with a growth-restricted fetus (5 cases out of 8) in comparison with the controls (14 cases). CONCLUSIONS: In subjects positive to uterine artery Doppler velocimetry analysis (Doppler analysis for pre-eclampsia screening), the fetal DNA concentration is higher than expected, in the absence of any other clinical feature. Since the increase in fetal DNA seems to be related to the presence or to the future development of intrauterine growth restriction, this paper suggests a possible integration between ultrasound and molecular markers for predicting the disease in some cases.