Rapid clearance of fetal DNA from maternal plasma

Non-invasive fetal sex determination using a conventional nested PCR analysis of fetal DNA in maternal plasma

BACKGROUND

In order to provide a reliable non-invasive method for fetal sex determination in a routine setting, we evaluated the possibility of identifying the fetal Y chromosome-specific sequence in maternal plasma using conventional PCR analysis.

METHODS

Fetal gender was determined in 31 pregnant women including one with a dizygotic twin pregnancy between 7 and 32 weeks of gestation using DNA extracted from 200 microl of each maternal plasma. The 198 bp SRY gene-specific sequence on Y chromosome and the 261 bp ATL1 gene-specific sequence on X chromosome were co-amplified in a multiplex nested PCR manner. The result was confirmed by routine analysis of fetal tissue obtained by invasive procedure or examination of newborns after delivery.

RESULTS

The 198 bp SRY-specific sequence was detected in 15 plasma samples obtained from pregnant women carrying male fetuses. In the remaining cases bearing female fetuses, only the 261 bp ATL1 gene sequence was detected, producing 100% sensitivity and specificity of fetal sex prediction. The result was completely concordant with the conventional fetal tissue analysis and examination of the newborns after delivery.

CONCLUSIONS

A conventional nested PCR analysis of maternal plasma could be used for accurate fetal gender detection and enable a reliable prospective non-invasive fetal sex determination which should enhance prenatal diagnostic options especially for sex-linked disorders.

Probing the fetal genome: progress in non-invasive prenatal diagnosis

Progress in our understanding of the molecular basis of heritable diseases, through identification of specific mutations, has provided a foundation for the development of DNA-based prenatal diagnosis. Genetic analysis of fetal DNA is now routinely performed from chorionic villus samples obtained as early as the tenth week of gestation or by amniocentesis from week 15 onwards. However, both of these approaches involve invasive procedures with increased risk of fetal loss. To avoid such complications, attempts have been made to develop non-invasive tests through the identification, characterization and isolation of fetal cells or free fetal DNA from the maternal circulation. Recently, progress has been made towards the development of novel strategies that are expected to provide non-invasive means for early prenatal diagnosis in pregnancy.

Time course of early and late changes in plasma DNA in trauma patients

BACKGROUND

Cell-free DNA concentrations increase in the circulation of patients after trauma and may have prognostic potential, but little is know concerning the temporal changes or clearance of the DNA or its relationships with posttraumatic complications. We investigated temporal changes in plasma DNA concentrations in patients after trauma with use of real-time quantitative PCR.

METHODS

Serial plasma samples were taken from two trauma populations. In the first study, samples were collected every 20 min from 25 patients within the first 3 h of trauma. In the second study, samples were collected every day from 36 other trauma patients admitted to the intensive care unit (ICU).

RESULTS

In the first study, plasma DNA was increased within 20 min of injury and was significantly higher in patients with severe injury and in patients who went on to develop organ failure. In patients with less severe injuries, plasma DNA concentrations decreased toward reference values within 3 h. In the second study, plasma DNA concentrations were higher in patients who developed multiple organ dysfunction syndrome between the second and fourth days of admission than in patients who did not develop the syndrome. In patients who remained in the ICU with continuing organ dysfunction, plasma DNA remained higher than in healthy controls even at 28 days after injury. Most survivors with multiple organ dysfunction syndrome showed an initial very high peak followed by a prolonged smaller increase.

CONCLUSIONS

Plasma DNA concentrations increase early after injury and are higher in patients with severe injuries and in those who develop organ failure. Increased plasma DNA persists for days after injuries, especially in patients with multiple organ dysfunction syndrome.

Fetal DNA in maternal serum: does it persist after pregnancy?

Fetal DNA and cells present in maternal blood have previously been used for non-invasive prenatal diagnosis. However, some fetal cells can persist in maternal blood after a previous pregnancy. Fetal rhesus status and sex determination have been performed by using amplification by real-time polymerase chain reaction (PCR) of fetal DNA sequences present in maternal circulation; no false-positive results related to persistent fetal DNA from a previous pregnancy have been reported. This idea has recently been challenged. An SRY real-time PCR assay was performed on the serum of 67 pregnant women carrying a female fetus but having previously given birth to at least one boy and on the serum of 30 healthy non-pregnant women with a past male pregnancy. In all cases, serum was negative for the SRY gene. These data suggest that fetal DNA from a previous pregnancy cannot be detected in maternal serum, even by using a highly sensitive technique. Therefore, non-invasive prenatal diagnosis by fetal sex determination for women at risk of producing children with X-linked disorders, and fetal RHD genotyping is reliable and secure as previously demonstrated.

Quantitative analysis of pleural fluid cell-free DNA as a tool for the classification of pleural effusions

BACKGROUND

Recently, much interest has been focused on the quantification of DNA in miscellaneous body fluids. In this study, the application is extended to classifying pleural effusions by measuring cell-free DNA in pleural fluid.

METHODS

We recruited 50 consecutive patients with pleural effusions with informed consent. Pleural fluids were centrifuged at 13000 g, with supernatants aliquoted for extraction and analysis of beta-globin DNA sequence by quantitative real-time PCR. Serum and pleural fluid biochemistries were performed to classify pleural effusions using the modified criteria of Light et al. (Ann Intern Med 1972;77:507-13). The ROC curve was plotted to determine the cutoff DNA concentration for classifying pleural fluids as transudates or exudates. Indicators of diagnostic accuracy were calculated for both pleural fluid DNA and modified criteria of Light et al., using the discharge, microbiologic, and histologic diagnoses as the reference standard.

RESULTS

The area under the ROC curve was 0.95 [95% confidence interval (CI), 0.84-0.99]. At 509 genome-equivalents/mL, pleural fluid DNA alone correctly classified 46 of 50 pleural effusions with 91% sensitivity (95% CI, 76-98%), 88% specificity (95% CI, 64-98%), and positive and negative likelihood ratios of 7.7 (95% CI, 3.1-19.5) and 0.10 (95% CI, 0.04-0.27), respectively. With the modified criteria of Light et al., 43 of 50 pleural effusions were correctly classified with 97% sensitivity (95% CI, 91-100%) and 67% specificity (95% CI, 45-89%). There were significant correlations between cell-free DNA and both lactate dehydrogenase and total protein in pleural fluid, suggesting their common origin.

CONCLUSIONS

Pleural fluid DNA concentrations are markedly increased in exudative effusions, making it a potential new tool to evaluate the etiologic causes of pleural effusions.

No evidence of fetal DNA persistence in maternal plasma after pregnancy

Short- and long-term persistence of fetal DNA in maternal plasma has been investigated. Short-term persistence at very low concentration was detected in 47 out of 105 women within two days after delivery. Twelve out of 13 samples re-tested within three days scored negative. No long-term persistence was detected in 172 women who had previous sons or abortions. Molecular microchimerism due to circulating fetal DNA persisting from previous pregnancies should not hamper non-invasive plasma-based prenatal testing.

The concentration of circulating corticotropin-releasing hormone mRNA in maternal plasma is increased in preeclampsia

BACKGROUND

Increased fetal DNA in maternal plasma/serum has been reported in pregnancies complicated by preeclampsia. We hypothesize that fetal RNA may also be increased in maternal plasma in preeclampsia.

METHODS

We developed a real-time quantitative reverse transcription-PCR assay to measure the concentration of the mRNA of the corticotropin-releasing hormone (CRH) locus. Peripheral blood samples were obtained from healthy pregnant women both before and 2 h after delivery. Peripheral blood samples were also obtained from women suffering from preeclampsia and controls matched for gestational age. Plasma was harvested from these samples, and RNA was extracted. Plasma RNA was subjected to analysis by the reverse transcription-PCR assay.

RESULTS

CRH mRNA was detected in the plasma of 10 healthy pregnant women in the third trimester. CRH mRNA was found to be cleared very rapidly after cesarean section, with no detectable signal by 2 h postpartum. Plasma CRH mRNA concentrations were 1070 and 102 copies/mL, respectively, in 12 preeclamptic women and 10 healthy pregnant women matched for gestational age (Mann-Whitney test, P <0.001).

CONCLUSION

Plasma CRH mRNA represents a new molecular marker for preeclampsia. Maternal plasma RNA is gender- and polymorphism-independent and may allow noninvasive gene-expression profiling of an unborn fetus.

Prognostic use of circulating plasma nucleic acid concentrations in patients with acute stroke

BACKGROUND

At present there is no simple, accurate blood test that may be used to determine the severity of stroke or to predict mortality and morbidity in stroke patients presenting to emergency departments.

METHODS

Patients with stroke-like symptoms who presented to an emergency department of a university hospital in Hong Kong were recruited for the study. DNA extracted from patients' plasma was analyzed for the beta-globin gene with a fluorescent-based PCR test. The primary outcome measures were in-hospital and 6-month mortality and morbidity using the post-stroke modified Rankin Score.

RESULTS

Among the 88 consecutive patients recruited to the study, 70 (80%) had ischemic stroke, 11 (13%) had intracerebral hemorrhage, and 7 (8%) had transient ischemic attacks. Median plasma DNA concentrations taken within 3 h of symptom onset were higher in patients who died compared with those who survived at discharge (6205 vs 1334 kilogenome-equivalents/L; P = 0.03). Among patients with NIH Stroke Scale scores >8, median plasma DNA concentrations were higher in patients who died compared with those who survived to 6 months (2273 vs 968 kilogenome-equivalents/L; P = 0.002). Plasma DNA concentrations correlated with the volume of cerebral hematoma (r = 0.66; P = 0.03). Plasma DNA concentrations >1400 kilogenome-equivalents/L had a sensitivity of 100% and a specificity of 74.4% for predicting hospital mortality after stroke, and the area under the ROC curve was 0.89 (95% confidence interval, 0.80-0.94). The adjusted odds ratio for plasma DNA concentrations predicting 6-month mortality was 1.6 (1.1-2.4; P = 0.03) and for predicting 6-month post-Rankin Score >2 was 1.8 (1.0-3.3; P = 0.05).

CONCLUSION

Plasma DNA concentrations correlate with stroke severity and may be used to predict mortality and morbidity in the emergency room.

Non-invasive prenatal diagnosis: on the horizon?

The launch of the genomics and postgenomics era has greatly expanded our understanding of the genetic basis of many diseases. In conjunction with the sociocultural trend to delay childbirth and to maintain smaller family units, extra demand may be placed on the existing prenatal diagnostic services. The inherent risk of fetal loss associated with current prenatal diagnostic procedures, such as amniocentesis and chorionic villus sampling, has spurred research into non-invasive prenatal diagnosis. Much research has been conducted on the exploitation of fetal genetic material present in the maternal circulation. The initial focus was on the isolation of intact fetal cells and subsequently, the existence of extracellular fetal DNA in maternal plasma was realized. Exciting developments have been achieved in recent years. A large-scale trial to evaluate the clinical utility of fetal cell isolation from maternal blood for fetal aneuploidy diagnosis was launched and data were recently published. Much has taken place in the research of fetal DNA analysis in maternal plasma and in one example, namely prenatal RhD determination, this type of analysis has been used in the clinical setting. This paper reviews the technological developments in non-invasive prenatal diagnosis.

Evaluation of the clinical usefulness of isolation of fetal DNA from the maternal circulation

OBJECTIVE

To assess the reliability of isolating free fetal DNA from maternal usefulness.

DESIGN

Fetal DNA was isolated from plasma or serum that was either collected prospectively or from archived samples collected for the purposes of second trimester screening.

METHODS

Prospective samples were collected from patients undergoing prenatal diagnostic procedures (n = 24). A second group of samples from Rhesus negative women (n = 28) were assayed in which blood had originally been collected for maternal triple serum screening. DNA was extracted from all samples and assayed for the presence of the beta-globin gene, sex-determing region Y (SRY) gene and Rh gene. All DNA sample handling and extraction was carried out by a single operator, and polymerase chain reaction (PCR) was carried out using previously published PCR primers and appropriate controls. The accuracy of results was assessed relative to the karyotype in the case of the SRY gene or cord blood phenotype in the case of the Rh gene.

RESULTS

The SRY PCR results were compared to fetal cell karyotypes obtained from invasive diagnostic testing, 21 out of the 24 samples were correctly 'sexed'. The RhD PCR results were compared to fetal cord blood samples at the time of delivery, and showed both false positive and false negative results. Two RhD negative babies were genotyped as RhD positive, despite repeat analysis.

CONCLUSION

It is possible to isolate fetal DNA from maternal serum. It is a potentially clinically useful technique in our laboratory and can be used to detect male fetuses, and Rh negative fetuses. To be useful in clinical practice, it is necessary to safeguard against contamination at the time of sample handling, and to use the optimal range of primers available to cover the polymorphisms present within the RhD gene. Although not robust enough yet to be used with diagnostic certainty in our hands, immense improvements in technique, probes and real-time PCR equipment make this type of diagnosis a reality in the near future.

Quantitative analysis of male fetal DNA in maternal serum of gravid rhesus monkeys (Macaca mulatta)

The isolation of human fetal DNA from the maternal circulation has provided a source of fetal material for prenatal diagnosis. The objective of this study was to investigate whether a similar pattern could be observed in the maternal circulation of male-bearing gravid rhesus monkeys. A real-time PCR TaqMan system for the rhesus Y-chromosome sex determining region was used to determine fetal sex and to quantify fetal DNA concentrations. Results in 14 healthy pregnancies indicated that fetal male DNA could be routinely detected in maternal serum by 50 d of gestation (late first trimester; term 165 +/- 10 d). Fetal DNA concentrations increased with advancing gestation, reaching a mean of 341 genome equivalents/mL of serum (range 11-1570 copies/mL) in the last trimester of gestation, similar to findings in humans. The fetal DNA concentration corresponded to 2.7% of the total maternal serum DNA in the third trimester. Similar to findings in humans, male fetal DNA sequences were not detected postpartum (through 4 wk postpartum) or in animals with a previous history of delivering male offspring. These data indicate that fetal male DNA is present in the maternal circulation of gravid rhesus monkeys comparable to findings in humans and further support the use of this nonhuman primate species as a model to investigate fetomaternal cell trafficking and microchimerism.

Earliest gestational age for fetal sexing in cell-free maternal plasma

OBJECTIVES

To evaluate at what gestational age fetal DNA can reliably be detected at the earliest in maternal plasma.

METHODS

We performed consecutive blood sampling in the first trimester of pregnancy in 17 women who were pregnant after in vitro fertilization (IVF) or intrauterine insemination (IUI). DNA was isolated and the Y-chromosome specific SRY was amplified by real-time polymerase chain reaction (PCR). We likewise studied 31 women prior to invasive prenatal diagnosis procedures for test validation purposes. All test results were compared to cytogenetic sex or sex at birth.

RESULTS

The earliest SRY detection was at a gestational age of 5 weeks and 2 days. In none of 4 pregnancies ending in a miscarriage was SRY detected. We detected SRY in maternal plasma in 1 of 2 patients (50%) carrying a male fetus at a gestational age of 5 weeks, in 4 of 5 (80%) at a gestational age of 7 weeks, in 4 of 4 (100%) at a gestational age of 9 weeks. In all 7 women pregnant with a male fetus, the correct fetal sex was detected by 10 weeks. In none of the 6 patients who delivered a girl was SRY detected. In the validation group, SRY was detected in 13 of the 13 male, and none of the 18 female fetuses.

CONCLUSIONS

We conclude that real-time PCR of the SRY gene promises to be a reliable technique for early fetal sexing in maternal plasma.

[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.

Limited expression of Fas and Fas ligand in fetal nucleated erythrocytes isolated from first trimester maternal blood

OBJECTIVE

Intact fetal cells isolated from maternal blood can be used for non-invasive gender determination and genetic diagnosis. Recent studies demonstrating a large amount of cell-free fetal DNA in maternal plasma suggest that the circulating fetal DNA may result from fetal cells undergoing apoptosis. In the present study we evaluated the potential role of Fas and Fas ligand (FasL) cell surface expression with respect to apoptosis induction in fetal cells isolated from maternal blood.

METHODS

We flow sorted candidate fetal cells that were gamma chain-positive and Fas- or FasL-positive or -negative, and subsequently analysed them by fluorescence in situ hybridization (FISH) analysis using X and Y chromosome-specific probes.

RESULTS

Among all gamma hemoglobin-positive cells, there was a significant difference in the percent of cells expressing Fas versus FasL (4.4 and 12.3, respectively). We found no significant correlation between the total number of fetal nucleated red blood cells (NRBCs) and gestational age or the presence of Fas- and FasL-positive cells. From approximately 7 ml of maternal peripheral blood, most of the confirmed fetal (XY) cells were found in the Fas- and FasL-negative sorted population; the average numbers were 12.8 and 15.7, respectively.

CONCLUSION

We conclude that fetal NRBCs express FasL more than Fas, although most fetal NRBCs in first trimester maternal blood samples do not express Fas or FasL. This suggests the absence of a functional Fas/FasL apoptotic system in fetal NRBCs, and that programmed cell death in these cells, which may lead to circulating fetal DNA in maternal plasma, probably occurs by another pathway.

Fetal DNA Clearance from Maternal Plasma Is Impaired in Preeclampsia

Background: Increased fetal DNA in maternal plasma/serum has been reported in pregnancies complicated by preeclampsia. We hypothesized that impaired clearance of fetal DNA might contribute, at least in part, to the above-mentioned phenomenon.

Methods: We studied 7 preeclamptic and 10 control pregnant women. All had male fetuses. Serial blood samples were obtained from before delivery to 6 h postpartum. Male fetal DNA in maternal plasma was measured by real-time quantitative PCR for the SRY gene on the Y chromosome.

Results: The median fetal DNA concentrations before delivery were significantly higher in the preeclamptic women than in the controls (521 vs 227 genome-equivalents/mL for preeclamptic and control women, respectively; Mann–Whitney rank-sum test, P = 0.017). The median fetal DNA concentrations at 6 h after delivery were also significantly different between the two groups (208 vs 0 genome-equivalents/mL for preeclamptic and control women, respectively; Mann–Whitney rank-sum test, P = 0.002). A first-order clearance model was found to best describe the kinetics of maternal plasma fetal DNA clearance. Moreover, we observed a significant difference in the median apparent clearance half-lives of fetal DNA between the preeclamptic women (114 min) and controls (28 min; Mann–Whitney rank-sum test, P = 0.007).

Conclusions: This study represents the first documentation of impaired fetal DNA clearance from maternal plasma in preeclampsia. Such an abnormality in circulating DNA clearance may also be present in other medical conditions associated with quantitative aberrations in circulating DNA concentrations.

Down syndrome and cell-free fetal DNA in archived maternal serum

OBJECTIVE

Increased levels of cell-free fetal DNA (f-DNA) in the maternal circulation are a potential noninvasive marker for fetal Down syndrome. Our objectives were to (1) determine whether f-DNA could be quantified by using archived serum and amniotic fluid, (2) examine whether serum f-DNA levels are elevated in Down syndrome pregnancies in a case-control series matched for gestational age and duration of sample storage, and (3) determine whether f-DNA levels are elevated in the amniotic fluid of Down syndrome fetuses.

STUDY DESIGN

Eleven serum and six amniotic fluid samples previously collected and stored at -20 degrees C from gravid women carrying a 47,XY,+21 fetus were each paired with five matched control samples of identical specimen type from gravid women carrying a presumed euploid male fetus. f-DNA concentration was quantified blindly by real-time polymerase chain reaction amplification for a Y-chromosome sequence. Matched rank-sum analysis and analysis of variance were used for analysis.

RESULTS

The mean observed rank of 5.0 in the Down syndrome group was significantly higher than expected (P </=.005). Adjusted mean serum f-DNA concentrations were 41.2 genomic equivalents (GE) per milliliter for the Down syndrome cases and 24.2 GE/mL for the euploid controls (P =.002). Differences among amniotic fluid samples were not statistically significant. There was a suggestion of a sample storage effect on f-DNA concentration on the order of -0.66 GE/mL per month (P =.071).

CONCLUSION

Down syndrome pregnancies exhibit 1.7-fold higher levels of maternal serum cell-free f-DNA compared with matched controls. No such association is observed in amniotic fluid. Archived serum appears to be a useful source of clinical material for retrospective analyses but may require controlling for the duration of sample storage.

Male microchimerism in healthy women and women with scleroderma: cells or circulating DNA? A quantitative answer

Male DNA, of presumed fetal origin, can be detected in the maternal circulation decades after delivery and is referred to as fetal microchimerism (FM). We previously found quantitatively greater FM in the circulation of women with the autoimmune disease scleroderma (SSc) than of healthy women. However, it is unknown whether this difference is due to intact circulating cells or free DNA released from breakdown in disease-affected tissues. To distinguish the origin of FM, we developed a real-time quantitative polymerase chain reaction (PCR) assay for the Y-chromosome-specific sequence DYS14, and tested 114 women in peripheral blood mononuclear cells (PBMCs) and/or plasma. Fifty-seven controls and 57 SSc patients were studied, 48 and 43 of whom, respectively, had given birth to at least one son. Circulating FM was quantitatively greater in PBMCs from SSc patients (n = 39; range, 0.0-12.5 male genome-equivalent cells per million maternal cells), compared with healthy women (n = 39; range, 0.0-4.4; P =.03). In contrast, there was no difference between patients (n = 25) and controls (n = 22) in plasma, and no evidence of free DNA. FM was enriched among T lymphocytes compared with PBMCs (P =.01) in controls (n = 14), but not in SSc patients (n = 14); the latter finding was most likely due to immunosuppressive medications. In conclusion, this real-time quantitative assay showed that quantitative differences in the circulation of women with SSc are due to cells and not to free DNA. As FM was not uncommon in healthy women, including among T cells, and because graft-versus-host disease has similarities to SSc, these results also suggest that FM merits investigation in pheresis products used for stem cell transplantation.

Non-invasive first trimester fetal gender assignment in pregnancies at risk for X-linked recessive diseases

OBJECTIVES

Prenatal diagnosis in families affected by X-linked recessive disorders should ideally be limited to the subjects at increased risk, i.e. male fetuses, in order to avoid the risk of fetal loss due to the invasive procedure in healthy female fetuses. The aim of the study was to assess the fetal sex within the first trimester of gestation by two non-invasive approaches, using ultrasonography and a molecular analysis of fetal DNA extracted from whole maternal blood with specific markers, in order to avoid invasive sampling in female fetuses.

METHODS

A total number of 18 fetuses at risk for an X-linked recessive disease were included in the present investigation. Maternal peripheral blood was analysed between 7 and 12 weeks of gestation by nested PCR for the detection of fetal DNA and the prediction of fetal gender. In addition, when the biparietal diameter (BPD) was between 21 and 23 mm, an ultrasonographic examination was carried out to assess the fetal gender. CVS was then performed in male fetuses only.

RESULTS

Fetal gender was correctly assigned by ultrasonography between 21 and 23 mm of BPD in all the cases studied, whereas DNA extracted from whole maternal blood accurately predicted the gender in all the female cases (10), but failed in 4 out of 8 male fetuses, erroneously assigned as females.

CONCLUSION

The present study shows that sonography is able to accurately predict the fetal gender within the first trimester of pregnancy, whereas the molecular analysis of DNA extracted from whole maternal blood is biased by false-Y-negative results in 50% of the cases.

Prenatal screening of single-gene disorders from maternal blood

Fetal cells and cell-free fetal DNA can be found circulating in maternal blood. Fetal cells recovered from maternal blood provide the only source of pure fetal DNA for noninvasive prenatal DNA diagnosis. Fetal nucleated erythrocytes (NRBCs) are considered the most suitable maternally-circulating fetal cells for this purpose, because they are not commonly found in the peripheral blood of healthy adults and are most abundant in the fetus during early gestation. Because fetal cells in maternal blood are extremely rare, a definitive separation method has not yet been established. Fetal NRBCs can be enriched from maternal blood via fluorescence- or magnetic-activated cell sorting, density gradients, immuno-magnetic beads or micromanipulation. Fetal cells are identified by Giemsa staining, hybridization with Y-chromosome specific probes, PCR-detection of a specific paternal allele, or immunostaining for fetal cell antigens. Amplification of fetal DNA sequences by primer extension preamplification and PCR has allowed prenatal screening for Duchenne muscular dystrophy and the fetal RhD blood type. Sequence-specific hybridization has been used to detect sickle cell anemia and beta-thalassemia prenatally in heterozygous carriers of these disorders. The use of cell-free fetal DNA in maternal plasma for the diagnosis of single-gene disorders is limited to disorders caused by a paternally inherited gene or a mutation that can be distinguished from the maternally inherited counterpart. At present, fetal gender can be determined from maternal plasma. When a pregnant woman is a heterzygous carrier of an X-linked disorder, the determination of fetal gender is clinically very informative for first-step screening to avoid invasive amniocentesis. The non-invasive prenatal diagnosis of genetic disorders should be applied to pregnant women with a definite risk for a specific single-gene disorder.

Epstein-Barr virus DNA in body fluids

Advances in polymerase chain reaction technology have greatly simplified the ability to detect and monitor Epstein-Barr virus DNA copy number in a variety of settings. An initial focus on cell-associated viruses by many investigators has shown some interesting results regarding the dynamics of Epstein-Barr virus infection. Several findings are unexpected. A relation between HIV load or CD4 T-cell counts and Epstein-Barr virus copy number is not seen. Furthermore, highly active antiretroviral treatment therapy in HIV patients that results in a rise of CD4 T cells may sometimes be associated with a rise in cell-associated Epstein-Barr virus load. Detection of Epstein-Barr virus in spinal fluid is useful in the diagnosis of primary central nervous system lymphoma, and monitoring of Epstein-Barr virus DNA copy number in spinal fluid may be useful in assessing response. Cell-free DNA in serum or plasma is emerging as a useful diagnostic tool in several settings. Fetal DNA can be detected in maternal serum or plasma. Tumor DNA can be detected in serum or plasma in association with a variety of cancers. Epstein-Barr virus DNA in serum or plasma has been found in infectious mononucleosis, nasopharyngeal carcinoma, posttransplant lymphoma, and nasal lymphoma. In each of these malignancies, its detection or quantification has been shown to be of prognostic significance. The utility of Epstein-Barr virus DNA detection and quantification in the serum or plasma of patients with HIV malignancies has yet to be determined but holds great promise.

Non-invasive determination of the paternal HLA haplotype of a fetus using kinetic PCR to detect fetal microchimerism in maternal plasma

Knowledge of fetal HLA type can be important if cord blood (CB) is being considered as a stem cell source for transplantation. The feasibility of determining the paternally inherited HLA haplotype of a fetus was explored through analysis of fetal DNA in the maternal circulation. A 5-year-old child with relapsed acute leukemia was a candidate for transplantation. The HLA type of the fetal sibling was needed to assist with evaluation of this potential cord blood donor. DNA was isolated from maternal plasma and whole blood. Kinetic PCR using sequence-specific primers for paternal HLA-A, -B, and -DRB1 alleles was performed. Alleles corresponding to one paternal haplotype were detectable in plasma, but not in whole blood. Alleles from the alternative haplotype were not detectable. This demonstrated that the fetus shared at least one haplotype with the patient and therefore arrangements were made to bank the CB. The maternal haplotype of the fetus could not be determined in the presence of maternal DNA. The prenatal fetal typing was confirmed by typing the newborn's CB. This rapid non-invasive technique may facilitate the selection of CB units for banking based on needed HLA types.

Prenatal diagnosis of genetic abnormalities using fetal CD34+ stem cells in maternal circulation and evidence they do not affect diagnosis in later pregnancies

In the present study, we report a new method for enrichment and analysis of fetal CD34+ stem cells after culture in order to determine whether it is feasible for noninvasive prenatal diagnosis. We also determined whether fetal CD34+ stem cells persist in maternal blood after delivery and assessed whether they have an impact on noninvasive prenatal diagnosis of genetic abnormalities. Peripheral blood samples were obtained from 35 pregnant women, 13 non-pregnant women who had given birth to male offsprings, 12 women who had never been pregnant, and eight pregnant women with male fetuses. CD34+ stem cells were enriched and either cultured for prenatal diagnosis or analyzed with fluorescence in situ hybridization (FISH)/polymerase chain reaction (PCR) to determine peristance in maternal blood. Fetal/maternal cells can be isolated and grown "in vitro" to provide enough cells for a more accurate fetal sex or aneuploid prediction than is provided by unenriched and uncultured CD34+ stem cells. The presence of fetal cells in maternal blood samples from mothers who had given birth to male offspring was found in 3 of 13 blood samples. PCR was positive for Y chromosome in one woman who had never been pregnant. Analysis of cultured CD34+ stem cells from mothers with Y PCR positivity did not detect any male cells in any samples. Even if PCR positivity is due to persistence of fetal stem cells from previous pregnancies, it does not seem to affect this new system of enrichment, culture, and FISH analysis of CD34+ fetal stem cells.

Persistence of tumor DNA in plasma of breast cancer patients after mastectomy

BACKGROUND

We investigated tumor DNA changes before and after mastectomy in the plasma of breast cancer patients with no disseminated disease and eventually investigated these changes' relationship to specific pathological parameters of the tumors.

METHODS

We studied 41 patients. DNA extracted from tumor and normal breast tissues, mononuclear blood cells, and plasma was used for molecular studies. Alterations in the microsatellite markers D17S855, D17S654, D16S421, TH2, D10S197, and D9S161, as well as point mutations in the p53 gene and aberrant methylation of p16(INK4a), were used to identify and characterize tumor and plasma DNA. A number of tumor clinicopathological parameters were analyzed in each patient.

RESULTS

We found that 18 (44%) of the 27 patients with alterations in tumor DNA presented the same plasma DNA alteration before mastectomy, and persistence of the same molecular features was detected in plasma DNA 4 to 6 weeks postmastectomy in 8 (19.5%) patients. Patients with vascular invasion, more than three lymph node metastases, and higher histological grade at diagnosis displayed plasma DNA after mastectomy with a significant difference.

CONCLUSIONS

Persistence of plasma DNA with features of tumor DNA may be present after mastectomy in breast cancer patients, and its relation to bad-prognosis histological parameters may suggest undetectable micrometastatic disease.

Significantly higher number of fetal cells in the maternal circulation of women with pre-eclampsia

Although the pathophysiology of pre-eclampsia is unknown, several studies have indicated that abnormal placentation early in pregnancy might play a key role. It has recently been suggested that this abnormal placentation may result in transfusion of fetal cells (feto-maternal transfusion) in women with pre-eclampsia. In the present study, fetal nucleated red blood cells were isolated from 20 women with pre-eclampsia and 20 controls using a very efficient magnetic activated cell sorting (MACS) protocol. The number of male cells was determined using two-color fluorescence in situ hybridization (FISH) for X and Y chromosomes. Significantly more XY cells could be detected in women with pre-eclampsia (0.61+/-1.2 XY cells/ml blood) compared to women with uncomplicated pregnancies (0.02+/-0.04 XY cells/ml blood) (Mann-Whitney U-test, p<0.001). These results suggest that fetal cell trafficking is enhanced in women with pre-eclampsia, and this finding may contribute to the understanding of the pathophysiology of the disease.

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.

Plasma DNA, prediction and post-traumatic complications

BACKGROUND

Trauma is a global public health problem that claimed 5.1 million lives in 1990. Twenty percent of these deaths occurred days to weeks after injury and were due to sepsis or organ failure. Therapies to improve survival outcome after injury are limited by our inability to accurately stratify trauma patients at risk for these complications. In this review, the challenge of predicting post-traumatic complications is presented. There is potential for plasma DNA in diagnosis, prediction and monitoring non-traumatic disease.

CONCLUSIONS

The mechanisms and clearance of plasma DNA have a potential role as a predictor in trauma.

Circulating fetal DNA in maternal plasma

BACKGROUND

The existence of high concentrations of circulating fetal DNA in maternal plasma may enable non-invasive prenatal diagnosis. There are many applications of fetal DNA in maternal plasma for clinical diagnosis.

CONCLUSIONS

We expect fetal DNA in material plasma will be incorporated into past of the prenatal investigation of pregnant women in the near future.

Quantitative analysis of Epstein-Barr virus DNA in plasma and serum: applications to tumor detection and monitoring

The recent interest in cell-free tumor-derived DNA in the plasma and serum of cancer patients has opened up numerous diagnostic possibilities. One type of tumor-derived DNA that has been detected in plasma/serum is viral DNA. One example of circulating viral nucleic acid is Epstein-Barr virus (EBV) DNA, which has been found in the plasma and serum of patients with nasopharyngeal carcinoma (NPC), certain lymphomas, and gastric carcinoma. Quantitative analysis of circulating EBV DNA in NPC has demonstrated a positive correlation with disease stage and a strong relationship with clinical events, as well as being of prognostic importance. For EBV-associated lymphomas, quantitative EBV DNA analysis has also been found to correlate closely with clinical progress. It is expected that plasma/serum EBV DNA analysis will soon be incorporated into the routine investigative protocol of EBV-associated malignancies.

Circulating nucleic acids and apoptosis

It is well documented that plasma contains DNA from tissues throughout the body, including developing fetuses, and tumors. A portion of this DNA crosses the kidney barrier and appears in urine (i.e., transrenal DNA). However, molecular, cellular, and physiological mechanisms of the circulating DNA phenomenon and renal clearance are in an early phase of investigation. Here, we discuss possible forms of circulating DNA, factors affecting representation of different tissues and genomic sequences in plasma DNA, possible mechanisms of renal DNA clearance, and technical problems encountered in DNA isolation from urine. We suggest that apoptotic cells are an important source of DNA in both plasma and urine. Further analysis of the data has led us to propose that a significant portion of circulating DNA can be represented in apoptotic bodies.

Effects of Blood-Processing Protocols on Fetal and Total DNA Quantification in Maternal Plasma

Background: Recently, apoptotic cells have been found in plasma obtained by centrifugation of blood from pregnant women, raising the question of what constitutes plasma and whether plasma is truly cell free. We compared the effects of different blood-processing protocols on the quantification, DNA composition, and day-to-day fluctuation of fetal and total DNA in maternal plasma.

Methods: Blood samples were collected from healthy pregnant women. The blood sample from each individual was simultaneously processed by different means, including the following: Percoll separation, centrifugation, microcentrifugation, and filtration. The resulting plasma aliquots were subjected to real-time quantitative amplification of the β-globin (for total DNA) and SRY (for fetal DNA) genes. The differences in the β-globin and SRY DNA concentrations and the degree of variation between the various plasma aliquots were assessed statistically.

Results: Different protocols of blood processing significantly affected the quantification and the day-to-day fluctuation of total (P &lt;0.001), but not fetal (quantification, P = 0.336; fluctuation, P = 0.206), DNA in maternal plasma. The quantitative difference could be attributed to the fact that efficacies of different protocols for generating cell-free plasma vary. Processing blood samples by centrifugation followed by filtration or microcentrifugation is effective in producing cell-free plasma.

Conclusions: Standardization in plasma-processing protocols is needed for maternal plasma DNA analysis, especially for quantification of total DNA in maternal plasma. Such preanalytic factors may also affect other applications of plasma DNA analysis.

Fetomaternal cellular and plasma DNA trafficking: the Yin and the Yang

In human pregnancy, multiple lines of evidence have indicated that there is trafficking of nucleated cells and cell-free DNA between the mother and fetus. Diagnostically, fetal cells in maternal blood and fetal DNA in maternal plasma offer a noninvasive source of fetal material for prenatal diagnosis. Through the developments of methods for fetal cell isolation and fetal DNA detection, many fetal genetic characteristics and chromosomal abnormalities have been detected from maternal blood. Large-scale clinical trials have been initiated that will facilitate the eventual application of these technologies. The presence of large quantities of cell-free fetal DNA in maternal plasma challenges the conventional belief that the fetal and maternal circulations are separate entities. In addition, the recent demonstration of the persistence of fetal cells following delivery also opens up a new field of investigation and raises new physiologic and pathogenic implications. Like the Yin and Yang in Chinese mythology, we believe that fetal cells and fetal DNA transfer are closely related and should be studied and applied in a synergistic manner.

Circulating nucleic acids in plasma and serum: an overview

The recent interest in nucleic acids in plasma and serum has opened up numerous new areas of investigation and new possibilities for molecular diagnosis. In oncology, tumor-derived genetic changes, epigenetic alterations, and viral nucleic acids have been found in the plasma/serum of cancer patients. These findings have important implications for the detection, monitoring, and prognostication of many types of malignancies. In prenatal diagnosis, the discovery of fetal DNA in maternal plasma and serum has provided a noninvasive source of fetal genetic material for analysis. This development has important implications for the realization of noninvasive prenatal diagnosis and has provided new methods for the monitoring of pregnancy-associated disorders. Plasma DNA technology has also found recent applications in the fields of organ transplantation, posttrauma monitoring, and infectious agent detection. Future areas of study include circulating RNA in plasma and the elucidation of the biology of release, clearance, and possible functionality of plasma nucleic acids.

Fetal DNA in maternal plasma: application to non-invasive blood group genotyping of the fetus

The non-invasive determination of fetal genetic characteristics, including blood group types, is a long-sought goal of modern genetics. Previous work on the use of fetal cells in maternal blood has been hampered by the rarity of such cells. The recent discovery of cell-tree fetal DNA in maternal blood has opened up new possibilities for non-invasive prenatal diagnosis. It is particularly useful that fetal DNA is present in relatively high concentrations in maternal plasma, making its robust detection possible using modern technology. Large-scale clinical trials and standardization of protocols still need to be carried out. However, there is optimism that the accurate and safe prenatal determination of fetal blood group types may be achieved in routine clinical practice in the near future.

Human natural chimerism: an acquired character or a vestige of evolution?

Analysis on five common classes of human natural chimeras (cytomictical, whole body, fetal-maternal, germ cell, and tumor chimeras) reveals that (1) they initiate only during pregnancy, (2) the most common class are chimeras which contain maternal cells, and (3) the primary mechanisms that are involved in their formation and establishment are still elusive. These classes of natural chimerism, are involved only with maladaptive phenomena such as malignancy and autoimmune diseases and without any documented benefit. A recent review has challenged the accepted dogma that the evolution of immunity is pathogen-directed and asserted that preserving individuality from littering the soma and the germline by conspecific alien cells might have been the original function of the innate immunity. Following this tenet, I propose here that human natural chimerism is a by-product of the new role evolved from primitive components of immunity to "educate" the developing embryo with the armamentarium of effector mechanisms, dedicated to purge the individual from pervasive somatic and germline variants, and is not a vestige of evolution.

Genotyping fetal DNA by non-invasive means: extraction from maternal plasma

BACKGROUND AND OBJECTIVES

Identification of fetal DNA in maternal plasma may allow genetic analysis without the use of invasive techniques. The aim of this study was to extract DNA from maternal plasma, identify fetal material through the presence of SRY or RHD gene sequences and assess the reliability of these results.

MATERIALS AND METHODS

A polymerase chain reaction (PCR) method of a commercial kit was used with primers for SRY or exon 10 of the RHD gene sequence.

RESULTS

Multiple plasma samples were collected from 60 women who were evaluable for either SRY or RHD, or both, fetally derived DNA sequences. Fetal DNA was present in the plasma throughout the pregnancies and for some hours or days after delivery.

CONCLUSION

Fetal DNA can be reliably detected in maternal plasma from early in pregnancy and normally is cleared within days of delivery.

Fetal cells in maternal blood

Fetal lymphocytes, trophoblasts, and nucleated red blood cells have each been separated from maternal blood by methods such as flow cytometry, magnetic cell sorting, and charge flow separation. The frequency of fetal cells among circulating maternal mononuclear cells remains to be ascertained. Current estimates range from about 10-5 to 10-7, but the numbers may be increased in women carrying aneuploid fetuses. Fetal cells separated from maternal blood have been studied by methods such as polymerase chain reaction and fluorescence in situ hybridization. Among fetal conditions so far identified are sex; human leukocyte antigen and Rh blood types; trisomy 13, 18 and 21; triploidy; and sickle cell anemia and thalassemia. Thus, fetal cell separation might one day be used for screening of the common aneuploidies and, ultimately, for prenatal diagnosis. Individual fetal erythroid precursors have been cultured after separation in some laboratories. Culturing and karyotyping of separated fetal cells might enable diagnosis of a spectrum of chromosomal and genetic disorders. Further development will be required, however, before regular clinical application of these methodologies.

Apoptosis in maternal peripheral blood during pregnancy

OBJECTIVE

To investigate the mononuclear cell apoptosis rate during pregnancy.

MATERIALS AND METHODS

Apoptosis was quantitated by EtBr staining in whole peripheral blood samples of 135 women in different gestational weeks and 85 nonpregnant women used as controls. Apoptosis was also qualitated by TUNEL assay.

RESULTS

The apoptosis rate increased during pregnancy according to gestational age. In chromosomally abnormal fetuses apoptosis was 2.5-fold higher than that found in pregnancies with normal embryos matched for gestational age. FISH in TUNEL-positive cells using X, Y and 21 chromosome probes verified the fetal origin of part of the apoptotic population.

CONCLUSION

Apoptosis is stimulated in maternal peripheral blood during pregnancy, possibly accounting partly for the presence of free fetal DNA in maternal serum. The increased apoptosis rate in pregnancies with chromosomally abnormal fetuses may have additional clinical importance.

Fetal DNA in Maternal Plasma: Biology and Diagnostic Applications

Background: Molecular analysis of plasma DNA during human pregnancy has led to the discovery that maternal plasma contains both fetal and maternal DNA. This valuable source of fetal DNA opens up new possibilities for noninvasive prenatal diagnosis.

Approach: Published data from the last 3 years demonstrating the feasibility and utility of analyzing fetal DNA in maternal plasma are reviewed.

Content: The detection of fetal DNA in maternal plasma is much simpler and more robust than detecting fetal nucleated cells in maternal blood, and does not require prior enrichment. This approach has been shown to have application in the prenatal diagnosis of fetal rhesus D status, sex-linked disorders, and other paternally inherited genetic disorders. Abnormal fetal DNA concentrations in maternal plasma and serum have been found in common pregnancy-associated disorders, including preterm labor and preeclampsia, as well as in pregnancies complicated by fetal trisomy 21. After delivery, fetal DNA is cleared rapidly from maternal plasma, with a half-life in the order of minutes. These clearance kinetics exhibit an important difference from fetal cell clearance, where long-term persistence has been demonstrated.

Summary: It has been only 3 years since fetal DNA was first detected in maternal plasma, and much remains to be learned about the biology of this phenomenon. In addition, additional diagnostic applications beyond those discussed here can be expected in the near future.

Prenatal detection of fetal Down's syndrome from maternal plasma

Fetal DNA is present in maternal plasma, and a proportion of such DNA is seen in intact fetal cells. We investigated the use of fluorescence in-situ hybridisation (FISH) techniques on maternal plasma samples. In plasma samples obtained from three women carrying fetuses affected by trisomy 21 (Down's syndrome), we identified fetal cells with three chromosome-21 signals. These results show the feasibility of non-invasive detection of fetal chromosomal aneuploidy by maternal plasma analysis.

Fetal cells in the mother: from genetic diagnosis to diseases associated with fetal cell microchimerism

Fetal cells circulate in the blood of pregnant women. When the gestation is normal, fetal cells are low in number. Complications of pregnancy, such as pre-eclampsia, or fetal cytogenetic abnormalities, such as Down's syndrome, increase fetomaternal transfusion. The isolation of fetal cells from maternal blood is currently under active investigation as a non-invasive method for prenatal diagnosis. The fetal cells that are most commonly used for non-invasive genetic diagnosis, the nucleated erythrocyte and the trophoblast, are highly differentiated and do not persist post-partum. In the context of studying fetal cells in maternal blood it was discovered that fetal progenitor cells originating from a prior pregnancy could also be detected. This led to the appreciation that unlike fetal DNA in plasma, which is cleared almost immediately following delivery, fetal cells persist for decades post-partum. Following pregnancy, labor, and delivery, a woman becomes a chimera. Transfused fetal stem and progenitor cells appear to be capable of further differentiation and migration to maternal organs. A further research agenda is needed to explore the newly appreciated phenomenon of bi-directional fetomaternal cell trafficking. Any consideration of the fetus as a patient must also consider the fetus as a potential source of therapeutic stem cells for the mother.

Cell-free fetal deoxyribonucleic acid in maternal circulation as a marker of fetal-maternal hemorrhage in patients undergoing external cephalic version near term

OBJECTIVE

Our aim was to investigate whether external cephalic version performed near term increases the concentration of cell-free fetal deoxyribonucleic acid in maternal plasma.

STUDY DESIGN

Forty-five patients who had singleton male fetuses and were undergoing external cephalic version at or beyond 36 weeks of gestation were recruited during a 20-month period. Maternal venous blood samples were taken before and within 10 minutes after external cephalic version. Deoxyribonucleic acid was extracted from the plasma samples. The amount of fetal deoxyribonucleic acid was quantified by means of the SRY gene on the Y chromosome as a fetal marker. The change in SRY gene concentration before and after external cephalic version was compared by paired sample t test.

RESULTS

There was a significant increase in the concentration of fetal deoxyribonucleic acid in maternal serum after external cephalic version (before, 296 +/- 209 copies per milliliter; after, 369 +/- 228 copies per milliliter; P =.014). This increase in the concentration of deoxyribonucleic acid was most profound among the nulliparous patients after a successful version and in the presence of a posterior placenta. The location of the placenta was found to be the most significant factor accounting for the change in the deoxyribonucleic acid concentration.

CONCLUSIONS

External cephalic version near term imposed a significant disturbance to the maternalplacental interface. Fetal deoxyribonucleic acid is a sensitive marker that is useful in the assessment of subclinical fetal-maternal hemorrhage.

Quantitative Analysis of the Bidirectional Fetomaternal Transfer of Nucleated Cells and Plasma DNA

Background: Recently, much interest has been generated on the fetomaternal transfer of nucleated cells and plasma DNA. However, there has been no systematic quantitative comparison of these two directions and two modalities of trafficking within the same study population.

Methods: The fetus-to-mother transfer of nucleated cells and plasma DNA in pregnant women carrying male babies was studied using a real-time quantitative PCR assay for the SRY gene. For mother-to-fetus transfer, real-time quantitative PCR assays for the insertion/deletion polymorphisms involving the glutathione S-transferase M1 and angiotensin-converting enzyme genes were used.

Results: Of the 50 informative mother-baby pairs, maternal DNA was detected in the cellular fraction of umbilical cord blood in 24% of cases (12 of 50), at a median fractional concentration of 2.6 × 10−4 (interquartile range, 1.7 × 10−4 to 3.6 × 10−4). In the plasma fraction of cord blood, maternal DNA was detected in 30% (15 of 50) of cases at a median fractional concentration of 3 × 10−3 (interquartile range, 1 × 10−3 to 1.6 × 10−2). For the other direction of trafficking, fetus-to-mother transfer of nucleated cells was detected in 26% of cases (13 of 50) at a median fractional concentration of 3.2 × 10−4 (interquartile range, 0.6 × 10−4 to 7.6 × 10−4). In the plasma fraction, fetal DNA was detected in 100% of maternal plasma (50 of 50) at a median fractional concentration of 3 × 10−2 (interquartile range, 1.4 × 10−2 to 5.3 × 10−2).

Conclusions: This study indicated that significantly more fetal DNA is present in the plasma of pregnant women compared with DNA from the cellular fraction of maternal blood. In addition, maternal DNA was demonstrated in both the cellular and plasma fractions of cord blood after delivery. This study has therefore determined the fundamental quantitative values for the bidirectional fetomaternal cellular and plasma DNA traffic.