Isolating fetal cells in maternal circulation for prenatal diagnosis

The Role of Fetal Membranes during Gestation, at Term, and Preterm Labor

During pregnancy, the fetal membranes (i.e., amniochorionic membranes) surround the intrauterine cavity and provide mechanical, immune, and endocrine support to protect the fetus. Though they are a vital component of the intrauterine cavity, the fetal membranes are largely overlooked as an extension of the placenta, leading to a poor understanding of their role during gestation, parturition, or preterm birth. The fetal membranes are comprised of fetal cellular and stromal layers and line up with maternal decidua forming the feto-maternal interface during pregnancy. This interface plays a large role during pregnancy and the induction of term or preterm parturition (e.g., labor). Here we summarize the function of the fetal membranes focusing on their role during gestation at term, and during preterm births.

Cytogenetics and Molecular Investigations detect a Mosaic Variant of Turner Syndrome only Suspected by Non-Invasive Prenatal Testing: Two Case Reports with Negative Ultrasound Examinations

Prenatal testing has been moving towards non-invasive methods to determine fetal risk for genetic disorders. Numerous studies have focused the attention on common trisomies; although the detection rate (DR) for trisomy 21 is high (over 95%), the accuracy regarding the DR for trisomies 13 and 18 has come under scrutiny. The testing has been applied to sex chromosome aneuploidies, but many studies have shown that it is not as effective as it is for common trisomies. Although non-invasive prenatal test (NIPT) has become a standard screening procedure for all pregnant women, invasive sampling procedures remain important in confirming NIPT-positive findings. In the present study, we report discordant results of Turner syndrome (TS) mosaicism between NIPT and karyotyping. A 35-year-old pregnant woman underwent NIPT, and a probable risk for Xp deletion was indicated. Subsequently, amniocentesis was performed. The karyotype was identified as mos 45,X [28]/46,X,i(X)(q1.0)[5]. In the second case, a 33-year-old woman underwent amniocentesis after a positive NIPT that indicated a probable risk for monosomy X. The result was mos 45,X [8]/46,XY[8]. Since NIPT is a screening test, the possibility of false-positive or false-negative results should always be considered. We underline the importance of pre/post detailed counseling. Furthermore, women with abnormal NIPT results should undergo immediate amniocentesis that remains the only tool for a correct diagnosis of sex chromosome aneuploidies.

High-purity isolation of rare single cells from blood using a tiered microchip system

We present a two-tiered microchip system to capture and retrieve rare cells from blood samples with high purity. The first module of the system is a high throughput microfluidic interface that is used to immunomagnetically isolate targeted rare cells from whole blood, and discard > 99.999% of the unwanted leukocytes. The second module is a microwell array that furthers the purification by magnetically guiding each cell into a separate well concurrently, and allows individual retrieval of each cell. We demonstrate the design of the system as well as its characterization by experiments using model cell lines that represent circulating fetal trophoblasts. Our results show that single cells can be retrieved with efficiencies and purities as high as 100% within 145 mins.

Low fetal fraction of cell-free DNA predicts placental dysfunction and hypertensive disease in pregnancy

OBJECTIVE

To examine the association of low fetal fraction of cell-free DNA (cfDNA) with placental compromise and adverse perinatal outcomes.

MATERIALS AND METHODS

This was a retrospective cohort utilizing a sample of convenience including 639 women undergoing cfDNA screening at our institution from January 2013 to January 2017. Low fetal fraction was defined as less than the 25th percentile. Indicators of placental compromise were examined individually and as a composite outcome, including hypertensive disease of pregnancy, intrauterine growth restriction, abruption, and oligohydramnios. Neonatal outcomes, including preterm delivery, low Apgar scores, and small for gestational age, also were examined. We calculated risk ratios (RR) and 95% confidence intervals (CI).

RESULTS

Low fetal fraction was associated with placental compromise (RR 1.6 [CI 1.1-2.2]), hypertensive disease of pregnancy (RR 1.6 [CI 1.003-2.6]), and preeclampsia with severe features (RR 3.3 [CI 1.2-8.9]). Low fetal faction was not associated with preterm delivery, low Apgar scores, or small for gestational age.

CONCLUSIONS

Low fetal fraction of cfDNA among asymptomatic women may serve as a predictor of subsequent placental dysfunction and hypertensive disease.

Cell-free fetal nucleic acid testing: a review of the technology and its applications

Cell-free fetal nucleic acids circulating in the blood of pregnant women afford the opportunity for early, noninvasive prenatal genetic testing. The predominance of admixed maternal genetic material in circulation demands innovative means for identification and analysis of cell-free fetal DNA and RNA. Techniques using polymerase chain reaction, mass spectrometry, and sequencing have been developed for the purposes of detecting fetal-specific sequences, such as paternally inherited or de novo mutations, or determining allelic balance or chromosome dosage. Clinical applications of these methods include fetal sex determination and blood group typing, which are currently available commercially although not offered routinely in the United States. Other uses of cell-free fetal DNA and RNA being explored are the detection of single-gene disorders, chromosomal abnormalities, and inheritance of parental polymorphisms across the whole fetal genome. The concentration of cell-free fetal DNA may also provide predictive capabilities for pregnancy-associated complications. The roles that cell-free fetal nucleic acid testing assume in the existing framework of prenatal screening and invasive diagnostic testing will depend on factors such as costs, clinical validity and utility, and perceived benefit-risk ratios for different applications. As cell-free fetal DNA and RNA testing continues to be developed and translated, significant ethical, legal, and social questions will arise that will need to be addressed by those with a stake in the use of this technology.

TARGET AUDIENCE

Obstetricians & Gynecologists and Family Physicians Learning Objectives: After participating in this activity, physicians should be better able to evaluate techniques and tools for analyzing cell-free fetal nucleic acids, assess clinical applications of prenatal testing, using cell-free fetal nucleic acids and barriers to implementation, and distinguish between relevant clinical features of cell-free fetal nucleic acid testing and existing prenatal genetic screening and diagnostic procedures.

Transfer of the amyloid β and/or of β-amyloid precursor protein of the fetus with trisomy 21 to the maternal blood stream and its possible contribution to the pathogenesis of the maternal Alzheimer's Disease

Down Syndrome (DS) is the most frequent genetic pathology. It affects 1 out of every 800 newborn babies. Approximately between a 90% and a 95% of all the cases of DS are attributed to a trisomy in chromosome 21. One of the genes contained in this chromosome is the gene of β-amyloid precursor protein (βAPP). The metabolism of this protein yields, among others, the amyloid beta peptides made up of 40 amino acids (Aβ40) and 42 amino acids (Aβ42). The evidence that is derived from several sources--genetic, among them--suggests that the Aβ participates in the pathogenesis of Alzheimer's Disease (AD). It is worth pointing at the fact that the transfer of cells, extracellular chromosomal material and some proteins from the fetus to the mother and vice versa has been widely described. The transfer rate from the fetus to the mother is higher when the mother is carrying a baby with trisomy 21. This has led to the hypothesis that sets forth that during the gestation of a baby with DS there is a greater fetomaternal transfer of cells and of products of the genes of chromosome 21--among them, βAPP and its metabolites Aβ40 and Aβ42. It is possible to speculate on the possible contribution of the fetal components--among them, Aβ--to the higher risk of suffering AD, which has been reported in a subpopulation of women who have given birth to children with DS. On the other hand, the detection of the βAPP--mainly intracellular--and of the β amyloid peptides in maternal blood and urine during the early stages of gestation could be taken as a potential non invasive biochemical prenatal marker of DS.

Prediction, prevention and personalisation of medication for the prenatal period: genetic prenatal tests for both rare and common diseases

Genetic testing usually helps physicians to determine possible genetic diseases in unborn babies, genetic disorders of patients and the carriers who might pass the mutant gene on to their children. They are performed on blood, tissues or other body fluids. In recent years, the screening tests and diagnostic tests have improved quickly and, as a result, the risks of pregnancy can be determined more commonly and physicians can diagnose several genetic disorders in the prenatal period. Detecting the abnormalities in utero enables correct management of the pregnancy, prenatal and postnatal medical care, and it is also important for making well informed decisions about continuing or terminating a pregnancy. Besides the improvements of conventional invasive diagnostic tests, the discovery of circulating cell-free foetal nucleic acids in maternal plasma has developed a new point of view for non-invasive prenatal diagnosis recently.

Prenatal diagnosis: update on invasive versus noninvasive fetal diagnostic testing from maternal blood

The modern obstetrics care includes noninvasive prenatal diagnosis testing such as first trimester screening performed between 11 and 14 weeks' gestation and second trimester screening performed between 15 and 20 weeks. In these screening tests, biochemical markers are measured in the maternal blood with or without ultrasound for fetal nuchal translucency with reported accuracy of up to 90%. Invasive procedures, including amniocentesis or chorionic villi sampling, are used to achieve over 99% accuracy. During these procedures direct fetal material is examined and, therefore, these tests are highly accurate with the caveat of a small risk for pregnancy loss. Much research now focuses on other noninvasive highly accurate and risk-free tests that will identify fetal material in the maternal blood. Fetal cells and fetal DNA/RNA provide fetal information but are hard to find in an overwhelming background of maternal cells and in the absence of specific fetal cell markers. The most experience has been accumulated with fetal rhesus and fetal sex determination from maternal blood, with an accuracy of up to 100% by using gene sequences that are absent from maternal blood. Although not clinically applicable yet, fetal cells, fetal DNA/RNA and fetal proteomics in combination with cutting edge technology are described to prenatally diagnose aneuploidies and single-gene disorders.

Identification of nucleated red blood cells in maternal circulation: a second step in screening for fetal aneuploidies and pregnancy complications

BACKGROUND

Identification of fetal nucleated red blood cells (NRBCs) in maternal circulation can facilitate non-invasive prenatal diagnosis, but technical difficulties still exist. An increase in the number of circulating NRBCs, however, could indicate fetal aneuploidies or pregnancy complications.

MATERIALS AND METHODS

The number of NRBCs was determined from 20 mL peripheral blood in 351 women in the second trimester of pregnancy after isolation by magnetic cell sorting (MACS) with anti-CD71 antibody and identification with May-Grunwald/Giemsa staining.

RESULTS

An average of eight NRBCs (range 1-12) were identified among 282 women with chromosomally normal fetuses. In cases known to carry aneuploid fetuses the mean number was 35 (range 7-113), but when the fetus had trisomy 21 (n = 17) an average of 71 NRBCs were identified. Among 26 carriers of beta-thalassemia, 42 NRBCs (range 22-158) were isolated. In pregnancies with abnormal Doppler findings in both uterine arteries (n = 20), 15 NRBCs (range 2-75) were isolated.

CONCLUSION

Determining the number of NRBCs in maternal circulation could represent an additional screening step for fetal aneuploidies, as long as the anemic status of the mother is taken into consideration. However, more cases with abnormal Doppler results must be investigated before this test is used for in the prediction of pregnancy complications.

Prenatal Diagnosis of Trisomy 21 with Fetal Cells in Maternal Blood Using Comparative Genomic Hybridization

OBJECTIVE

This study was undertaken to determine the clinical use of comparative genomic hybridization (CGH) for detection of fetal trisomy 21 from fetal ceIls (nucleated red blood cells; nRBCs) isolated from maternal peripheral venous blood.

METHODS

Maternal peripheral venous blood samples were collected in sterile tubes containing heparin. After triple density gradient centrifugation, magnetic activated cell sorting using CD45 and CD71 was used to isolate the fetal nRBCs. Fetal nRBCs were successfully isolated from maternal peripheral blood in all cases. After laser-microdissecting fetal nRBCs, degenerate oligonucleotide-primed polymerase chain reaction, and nick translation, DNA size was suitable for hybridization.

RESULTS

By CGH analysis, we diagnosed one normal male, one normal female, and one trisomy 21 male fetus. These results were confirmed by amniocentesis.

CONCLUSIONS

Prenatal diagnosis from fetal cells in maternal peripheral blood by CGH shows clinical promise as an alternative or as a supplement to fluorescence in situ hybridization with chromosome-specific probes but further studies are warranted.

Analysis of cell-free fetal DNA in plasma and serum of pregnant women

Sixty blood samples from pregnant women during gestational weeks 9-28 were investigated. Cell-free fetal DNA was extracted from maternal plasma or serum to be detected by nested PCR for determination of fetal gender. The SRY gene as a marker for fetal Y chromosome was detected in 34/36 women carrying a male fetus. In 3/24 women carrying female fetuses, the SRY sequence was also detected. Overall, fetal sex was correctly predicted in 91.7% of the cases. Therefore, the new, non-invasive method of prenatal diagnosis of fetal gender for women at risk of producing children with X-linked disorders is reliable, secure, and can substantially reduce invasive prenatal tests.

Culture of Cells from Maternal Circulation, in Conditions Favoring Fetal Endothelial Cell Expansion, Does Not Facilitate the Preferential Expansion of Circulating Fetal Cells

OBJECTIVES

To establish optimal culture conditions for fetal endothelial cells, and determine whether these can be used for preferential expansion of fetal cells from maternal blood.

METHODS

Human adult microvascular and umbilical vein endothelial cells were cultured in the presence of colony-stimulating factor-1 (CSF-1), placental growth factor (PlGF), and transforming growth factor-beta1 (TGF-beta1). The effect of each cytokine was assessed. We expanded peripheral blood mononuclear cells (PBMCs) from 18 pregnant women using the conditions most favorable to fetal cells; in specimens from women carrying male fetuses (n = 9), cell origin was determined by PCR (SRY locus).

RESULTS

The optimal concentrations of CSF-1, PlGF and TGF-beta1 were 10, 100, and 5 ng/ml, respectively. PBMCs from maternal blood expanded in the presence or absence of the cytokines; PCR analysis showed no Y sequences in cultured maternal samples.

CONCLUSION

Optimal concentrations of CSF-1, PlGF and TGF-beta1 for preferential expansion of fetal endothelial cells were determined in model cultures. However, when these conditions were applied to maternal blood samples, no fetal cells could be detected based on PCR for SRY in women carrying male fetuses.

Application of fetal DNA in maternal plasma in noninvasive prenatal diagnosis

To explore the application of fetal DNA in maternal plasma for noninvasive prenatal diagnosis, the DNA template was extracted by hydroxybenzene-chloroform from 44 maternal (7-41 weeks) plasma. The Fetus-derived Y sequence DYZ-1 gene (149bp) was chosen to be amplified by PCR. The fragment was identified in all the plasma of male bearing pregnant women with the diagnostic accordance rate being 100.00%. Two of the 22 female bearing pregnant women had false positive results. Among the 44 pregnant women, the diagnostic accordance rate was 88.89% at early pregnant stage, 100.00% at medium pregnant stage, and 96.55% at late stage respectively. The final accuracy of 95.45% was obtained in all cases. It was concluded that by means of hydroxybenzene-chloroform extraction the authors of this article promoted the concentration and purity of the DNA template, and diagnosed more accurately. The results showed that free fetal DNA in the maternal plasma could be regarded as the gene resource for noninvasive prenatal diagnosis.

Advances in prenatal screening for Down syndrome: I. general principles and second trimester testing

BACKGROUND

Down syndrome is one of the most important causes of mental retardation in the population. In the absence of prenatal screening and diagnosis, prevalence at birth in the United States would currently exceed 1:600. The purpose of prenatal screening is to identify those women at the increased risk for an affected pregnancy and to maximize the options available to these women.

TESTS AVAILABLE

Second trimester serum screening involves combining the maternal age-specific risk for an affected pregnancy with the risks associated with the concentrations of maternal serum alpha-fetoprotein (MSAFP), unconjugated estriol (uE3), and human chorionic gonadotropin (hCG) (triple testing). A forth analyte, inhibin-A (INH-A), is increasingly being utilized (quadruple testing). Optimal second trimester screening requires the integration of a number of clinical variables, the most important of which is an accurate assessment of gestational age. In addition to Down syndrome, the triple and quadruple tests preferentially identify fetal trisomy 18, Turner syndrome, triploidy, trisomy 16 mosaicism, fetal death, Smith-Lemli-Opitz syndrome, and steroid sulfatase deficiency. Some programs modify the Down syndrome risks generated through maternal serum screening tests with fetal biometric data obtained by ultrasound. Other second trimester tests have shown promise, including the analysis of maternal urine and fetal cells in the maternal circulation, but none are in routine clinical use.

CONCLUSION

The second trimester triple and quadruple tests provide benchmarks for evaluating new screening protocols. The combination of fetal biometry, new test development as well as clarification of the role of co-factors that affect the concentrations of analytes in existing tests should lead to greater efficacy in second trimester screening for Down syndrome.

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.

Prenatal diagnosis on fetal cells obtained from maternal peripheral blood: report of 66 cases

The potential use of fetal cells circulating in maternal blood for a non-invasive prenatal diagnosis has been widely described. Several authors have developed different methods for the enrichment of fetal cells from maternal peripheral blood. The aim of this study was to make a practical valuation of this new prenatal diagnosis technique, using those methods described as efficient and easy to carry out in a prenatal diagnosis unit. These methods consist of the double-density gradient and the positive selection by magnetic activated cell sorting (MACS) of the fetal erythroblasts, and the posterior study of the cells applying the FISH interphasic technique. Once the technique was ready, we obtained results from the study of 66 venous blood samples from women coming for prenatal diagnosis. Using a specific staining for fetal haemoglobin, fetal cells were identified in 63 cases. Fetal sex was well determined in 56 cases, 23 females and 33 males; in 7 cases the sex determination failed. All the aneuploidies found in a previous prenatal diagnosis were confirmed.

Investigation of maternal blood enriched for fetal cells: role in screening and diagnosis of fetal trisomies

Prenatal diagnosis of chromosomal abnormalities relies on assessment of risk followed by invasive testing in the group with highest risk. Assessment of risk by a combination of maternal age and fetal nuchal translucency and invasive testing in the 5% of the population with the highest risk would identify about 80% of trisomy 21 pregnancies. Preliminary reports suggest that chromosomal abnormalities can also be diagnosed by fluorescent in situ hybridization (FISH) in maternal blood enriched for fetal cells. This study examines the potential role of this method on the prenatal diagnosis of fetal trisomies. Maternal blood was obtained before invasive testing in 230 pregnancies at 10-14 weeks of gestation. After enrichment for fetal cells, by triple density centrifugation and anti-CD71 magnetic cell sorting, FISH was performed and the proportion of cells with positive signals in the chromosomally normal and abnormal groups was determined. Fetal karyotype was normal in 150 cases and abnormal in 80 cases, including 36 with trisomy 21. Using a 21 chromosome-specific probe, three-signal nuclei were present in at least 5% of the enriched cells from 61% of the trisomy 21 pregnancies and in none of the normal pregnancies. For a cut-off of 3% of three-signal nuclei the sensitivity for trisomy 21 was 97% for a false positive rate of 13%. Similar values were obtained in trisomies 18 and 13 using the appropriate chromosome-specific probe. Examination of fetal cells from maternal blood may provide a noninvasive prenatal diagnostic test for trisomy 21 with the potential of identifying about 60% of affected pregnancies. Alternatively, this technique can be combined with maternal age and fetal nuchal translucency as a method of selecting the high-risk group for invasive testing. Potentially, 80% of trisomy 21 pregnancies could be identified after invasive testing in less than 1% of the pregnant population.

Detection of foetal cells in maternal blood and prenatal sex determination by in situ hybridization. Procedure verification

We describe an enrichment of foetal cells from maternal blood with a combination of double density gradient and Magnetic Activated Cell Sorting (MACS) of CD71, glycophorin A (GPA), CD34 and CD36 antibodies labeled cells followed by fluorescence in situ hybridization (FISH) with chromosome-specific DNA probes for determination of foetal sex.

The micro-robotic laboratory: optical trapping and scissing for the biologist

With the addition of tightly focused laser beams, microscopes have been turned into elaborate preparative tools that permit not only allow detailed observation of a specimen but also the capture, displacement, and microdissection of biological samples in vitro with astonishing ease and accuracy. Laser-Tweezers are used to capture and manipulate cells and organelles. LaserScissors are used to perform microdissections at the submicrometer level. After a short technical description of the instrumentation and its principles of operation, several examples of applications are given relevant to the field of clinical research that could only be achieved using such modern technology. For instance, LaserTweezers and LaserScissors offer a unprecedented means to study the immune response to cancer, to control the growth of nerve cells, or expand the significance of assisted reproductive technologies. It is suggested that newly developing procedures and assays using laser-assisted technologies will prove beneficial for future clinical laboratory testing.

Bioethics of the refusal of blood by Jehovah's Witnesses: Part 1. Should bioethical deliberation consider dissidents' views?

Jehovah's Witnesses' (JWs) refusal of blood transfusions has recently gained support in the medical community because of the growing popularity of "no-blood" treatment. Many physicians, particularly so-called "sympathetic doctors", are establishing a close relationship with this religious organization. On the other hand, it is little known that this blood doctrine is being strongly criticized by reform-minded current and former JWs who have expressed conscientious dissent from the organization. Their arguments reveal religious practices that conflict with many physicians' moral standards. They also suggest that a certain segment of "regular" or orthodox JWs may have different attitudes towards the blood doctrine. The author considers these viewpoints and argues that there are ethical flaws in the blood doctrine, and that the medical community should reconsider its supportive position. The usual physician assumption that JWs are acting autonomously and uniformly in refusing blood is seriously questioned.

Prenatal diagnosis with use of fetal cells isolated from maternal blood: five-color fluorescent in situ hybridization analysis on flow-sorted cells for chromosomes X, Y, 13, 18, and 21

OBJECTIVE

Currently, prenatal diagnosis of chromosome abnormalities requires invasive techniques such as amniocentesis and chorionic villus sampling that carry small but finite risks of fetal loss. A noninvasive approach is to isolate fetal cells from maternal blood by flow sorting followed by genetic interphase analysis with fluorescence in situ hybridization. Because the ratio of fetal to maternal cells is relatively low after flow sorting and to detect 90% to 95% of fetal aneuploidies associated with serious birth defects, a 5-color fluorescent in situ hybridization strategy is necessary for simultaneous detection of chromosomes X, Y, 13, 18, and 21 in all flow-sorted nuclei recovered from a specimen.

STUDY DESIGN

Fetal nucleated red blood cells were isolated from maternal blood in 40 cases (10.4 to 27.0 weeks' gestation) by flow cytometry on the basis of positive selection of CD71+ (transferrin receptor), CD45-, and LDS751 staining. Each case was evaluated for 5-color fluorescent in situ hybridization efficiency by determining the percentage of flow-sorted nuclei containing 8 hybridization signals for chromosomes X, Y, 13, 18, and 21.

RESULTS

A total of 42,312 flow-sorted nuclei from maternal blood samples were analyzed. In 5 of 16 (31%) cases with a male fetus, 0.16% of nuclei scored were identified as fetal by the presence of 1 signal each for chromosomes X and Y. Fetal trisomy 21 nuclei were accurately detected in 2 cases with a female fetus, each of which was subsequently confirmed.

CONCLUSIONS

Five-color interphase fluorescent in situ hybridization analysis can be used to effectively analyze rare fetal aneuploid nuclei in enriched flow-sorted cells isolated from maternal blood.

Integrated cell isolation and polymerase chain reaction analysis using silicon microfilter chambers

White blood cells are isolated from whole blood in silicon-glass 4.5-microliter microchips containing a series of 3.5-micron feature-sized 'weir-type' filters, formed by an etched silicon dam spanning the flow chamber. Genomic DNA targets, e.g., dystrophin gene, can be directly amplified using the polymerase chain reaction (PCR) from the white cells isolated on the filters. This dual function microchip provides a means to simplify nucleic acid analyses by integrating in a single device two key steps in the analytical procedure, namely, cell isolation and PCR.

Antenatal screening for Down's syndrome

BACKGROUND

In 1968 the first antenatal diagnosis of Down's syndrome was made and screening on the basis of selecting women of advanced maternal age for amniocentesis was gradually introduced into medical practice. In 1983 it was shown that low maternal serum alpha fetoprotein (AFP) was associated with Down's syndrome. Later, raised maternal serum human chorionic gonadotrophin (hCG), and low unconjugated oestriol (uE3) were found to be markers of Down's syndrome. In 1988 the three biochemical markers were used together with maternal age as a method of screening, and this has been widely adopted. PRINCIPLES OF ANTENATAL SCREENING FOR DOWN'S SYNDROME: Methods of screening need to be fully evaluated before being introduced into routine clinical practice. This included choosing markers for which there is sufficient scientific evidence of efficacy, quantifying performance in terms of detection and false positive rates, and establishing methods of monitoring performance. Screening needs to be provided as an integrated service, coordinating and managing the separate aspects of the screening process. SERUM MARKERS AT 15-22 WEEKS OF PREGNANCY: A large number of serum markers have been found to be associated with Down's syndrome between 15 and 22 weeks of pregnancy. The principal markers are AFP, hCG or its individual subunits (free alpha- and free beta-hCG), uE3, and inhibin A. Screening performance varies according to the choice of markers used and whether ultrasound is used to estimate gestational age (table 1). When an ultrasound scan is used to estimate gestational age the detection rate for a 5% false positive rate is estimated to be 59% using the double test (AFP and hCG), 69% using the triple test (AFP, hCG, uE3), and 76% using the quadruple test (AFP, hCG, uE3, inhibin A), all in combination with maternal age. Other factors that can usefully be taken into account in screening are maternal weight, the presence of insulin dependent diabetes mellitus, multiple pregnancy, ethnic origin, previous Down's syndrome pregnancy, and whether the test is the first one in a pregnancy or a repeat. Factors such as parity and smoking are associated with one or more of the serum markers, but the effect is too small to justify adjusting for these factors in interpreting a screening test.

URINARY MARKERS AND FETAL CELLS IN MATERNAL BLOOD

Urinary beta-core hCG has been investigated in a number of studies and shown to be raised in pregnancies with Down's syndrome. This area is currently the subject of active research and the use of urine in future screening programmes may be a practical possibility. Other urinary markers, such as total oestriol and free beta-hCG may also be of value. Fetal cells can be identified in the maternal circulation and techniques such as fluorescent in situ hybridisation can be used to identify aneuploidies, including Down's syndrome and trisomy 18. This approach may, in the future, be of value in screening or diagnosis. Currently, the techniques available do not have the performance, simplicity, or economy needed to replace existing methods.

DEMONSTRATION PROJECTS

Demonstration projects are valuable in determining the feasibility of screening and in refining the practical application of screening. They are of less value in determining the performance of different screening methods. Several demonstration projects have been conducted using the triple and double tests. In general, the uptake of screening was about 80%. The screen positive rates were about 5-6%. About 80% of women with positive screening results had an invasive diagnostic test, and of those found to have a pregnancy with Down's syndrome, about 90% chose to have a termination of pregnancy. ULTRASOUND MARKERS AT 15-22 WEEKS OF PREGNANCY: There are a number of ultrasound markers of Down's syndrome at 15-22 weeks, including nuchal fold thickness, cardiac abnormalities, duodenal atresia, femur length, humerus length, pyelectasis, and hyperechogenic bowel. (ABSTRA

Characterization of fetal haematopoietic progenitors circulating in maternal blood of seven aneuploid pregnancies

A retrospective study was carried out in order to investigate the phenotype of fetal haematopoietic progenitors circulating in the maternal blood of seven aneuploid pregnancies. Five of the blood samples were taken during pregnancies affected by various fetal aneuploidies, while the other two were collected after therapeutic abortion due to prenatal cytogenetic diagnosis of trisomies 21 and 18. Haematopoietic progenitor cells, isolated by labelling the erythropoietin receptors with the biotinylated ligand before magnetic sorting and/or fibronectin cell adhesion assay, were cultured in a suitable semisolid medium. Single- or dual-colour fluorescence in situ hybridization (FISH) was utilized to identify and enumerate fetal cells amplified in culture. Fetal trisomies were confirmed in the FISH analysis with chromosome-specific probes in all the cases analysed. The fetal purity rate ranged from 16 to 26 per cent. Haematopoietic progenitors of fetal origin were found to include CFU-E, CFU-GEMM, and possibly also M-BFU-E. Interestingly, a more immature progenitor with high self-renewal capacity (CFU-blast cell) isolated by fibronectin sorting was shown to have a relatively high frequency in one case of Down syndrome. In general, the results of this study demonstrate the feasibility of diagnosing the major fetal chromosomopathies by culturing fetal cells taken from maternal blood. Furthermore, our initial data on the sequential sorting for fibronectin and erythropoietin receptors lead us to believe that this approach may broaden the range of fetal haematopoietic progenitors retrievable from the maternal circulation.

Noninvasive first-trimester screening for fetal aneuploidy

We reviewed all studies concerning noninvasive first trimester screening for fetal aneuploidy obtained from a MEDLINE search through June 1996 with additional sources identified through cross-referencing. Three screening and diagnostic modalities are of potential application in noninvasive first trimester testing for fetal aneuploidy: ultrasound, maternal biochemical markers, and analysis of fetal cells retrieved from maternal sources. Sensitivities of the sonographic finding of nuchal translucency thickness in combination with maternal age for trisomy 21, performed between 10 and 14 weeks of gestation in experienced hands, and maternal biochemical markers independently may be as high as 86 percent and 60 percent, respectively. Sensitivity, specificity, and predictive values of these diagnostic modalities alone, in combination with each other, or in conjunction with other predisposing factors such as maternal age, in large low risk populations have not currently been established. Analysis of fetal cells retrieved from maternal sources, although more complex, may offer definitive noninvasive prenatal diagnosis yet is not currently available in clinical practice. We conclude that noninvasive first trimester screening for fetal aneuploidy modalities including sonographic examination for nuchal translucency thickness and maternal biochemical markers, is feasible. Clinical feasibility; and all-encompassing clinical management paradigms of these and other early noninvasive first trimester screening methods for fetal aneuploidy, are not yet available.

Prenatal diagnosis of Duchenne and Becker muscular dystrophy

Prenatal diagnosis of Duchenne and Becker muscular dystrophy is performed as a routine procedure in many laboratories around the world, using numerous molecular genetic techniques. Rather than discussing methods that are commonly in use, this review concentrates on some of the methods that are less widely available. This includes techniques than can be applied to routine diagnosis, to difficult cases where DNA analysis is unhelpful, and alternatives to standard methods of prenatal diagnosis.

Culture of fetal erythroid progenitor cells from maternal blood for non-invasive prenatal genetic diagnosis

Fetal committed erythroid progenitors CFU-E and M-BFU-E released into the maternal circulation during pregnancy are ideal candidates for in vitro proliferation since their lifespan is short and they can form colonies of 100-1000 cells in a semi-solid medium. In order to propagate these cells with a high rate of purity, a strategy was devised based on their prior enrichment with biotin-labelled human erythropoietin ligand and magnetic sorting before culturing in a suitable medium. Eight euploid pregnancies investigated in order to address this issue produced fetal clones in cultures with 18 per cent purity as assessed by polymerase chain reaction (PCR) analysis for Y-specific sequences, immunocytochemical staining for fetal gamma-globin, and fluorescence in situ hybridization (FISH) study. The CFU-E-type colony was the most represented progenitor, followed by M-BFU-E, and only occasionally was the detection of CFU-GEMM recorded. The retrospective diagnosis of two cases of fetal Down's syndrome by culturing fetal cells from maternal blood was accomplished for the first time. FISH analysis disclosed a strong presence of fetal trisomic cells (70 per cent and 40 per cent in the two cases). This strong presence would suggest a preferential leakage into maternal blood. The overall results of this study demonstrate that fetal cells can be cultured in vitro with reliable reproducibility, thus making the prospect of a non-invasive prenatal genetic diagnosis realistic.

Enrichment of fetal trophoblast cells from the maternal peripheral blood followed by detection of fetal deoxyribonucleic acid with a nested X/Y polymerase chain reaction

OBJECTIVE

Fetal cells circulate in the maternal blood during early pregnancy. Because these cells are rare, noninvasive prenatal diagnosis from fetal cells can be achieved only after efficient enrichment procedures. Our aim was to develop a two-step enrichment procedure to isolate trophoblast cells from 20 ml of peripheral blood.

STUDY DESIGN

Blood was obtained from pregnant women between 6 and 15 weeks of gestation, before invasive procedures were performed. After enrichment, the success of isolating fetal cells was determined by amplification of Y chromosome sequences.

RESULTS

A highly specific X/Y polymerase chain reaction was established, sensitive enough to detect X and Y chromosome-specific sequences in one single cell and in one male among 100,000 female cells. Sex determination by polymerase chain reaction was compared with results from conventional karyotyping. The success rate was 91.7%.

CONCLUSION

Enrichment of trophoblast cells from maternal blood as described here might be useful for early noninvasive prenatal diagnosis.

Prenatal diagnosis by analysis of fetal cells in maternal blood

The data accumulated thus far indicate that fetal NRBCs are the target cell type of choice in maternal blood for most investigators, although some groups continue to work with the trophoblast. Reports of persistent circulation of hematopoietic stem cells, lymphoid/myeloid progenitors, and lymphocytes mandate that removal of these cell types must occur before clinical diagnosis of the current pregnancy can be made. In selected cases, accurate detection of fetal aneuploidy has been made from fetal cells in maternal blood; the clinical evaluation sponsored by the National Institute of Child Health and Human Development will determine the sensitivity and specificity of cytogenetic diagnosis in a larger group of pregnant women, but this information will not be available for several years. At present, detection of uniquely fetal, paternally inherited gene polymorphisms or mutations such as the Rh(D) antigen is possible only because the mother lacks these genes; hence, maternal cell contamination does not hinder diagnosis. Currently the presence of large numbers of maternal cells in enriched samples precludes single-gene diagnosis for conditions in which the mother carries a mutant gene, because her cells are preferentially amplified and difficult to distinguish from those of the fetus. It is likely, however, that as techniques of individual fetal cell isolation are perfected, maternal cell contamination will no longer be an issue, and the entire fetal genome will become available for diagnosis and therapy. Pediatricians need to be aware of the progress of research in this field, because fetal cell isolation from maternal blood not only could change prenatal diagnosis but would change the amount of genetic information that arrives with a newborn infant at birth. The ultimate goal of this work is to diagnose noninvasively, in the first trimester, the common fetal aneuploidies and single-gene disorders, to permit in utero treatment, or to allow low-risk pregnant women carrying an abnormal fetus an opportunity for reproductive choice.

Detection of low-grade mosaicism in fetal cells isolated from maternal blood

Recovering and analysing fetal erythrocytes from maternal blood is being pursued for non-invasive prenatal genetic diagnosis. We report the observation of 46,XY/47,XXY mosaicism in fetal cells from a woman whose first-trimester chorionic villus sampling (CVS) initially showed only 46,XY. Only after exhaustive (500 cells) analysis were four XXY cells found in cultured villi.

Isolation of fetal cells from transcervical samples by micromanipulation: molecular confirmation of their fetal origin and diagnosis of fetal aneuploidy

Transcervical cell (TCC) samples have been shown to contain fetal cells amenable to molecular analysis. However, the presence of 'contaminating' maternal cells limits their use for prenatal diagnoses. In this report we show that clumps of fetal cells can be isolated from transcervical samples by micromanipulation and tested by fluorescence in situ hybridization (FISH) and polymerase chain reaction (PCR). Out of 129 clumps, isolated from mucus aspirates and transcervical lavages from 29 patients, 29 clumps from 11 patients were found to be exclusively of fetal origin as judged by the detection of chromosome 21-specific polymorphic DNA markers and Y-derived DNA sequences by PCR and FISH. One case of a male triploid fetus, diagnosed by the analysis of TCC samples obtained by mucus aspiration and lavage, was confirmed by testing clumps of cells isolated by micromanipulation.

FISH in genome research and molecular diagnostics

Fluorescence in situ hybridization (FISH) has profoundly altered the aspect of genome research and molecular diagnostics. Deletions of only a few kilobases can be detected by hybridizing probes to naked DNA fibers. Loss or gain of chromosomal material in tumor cells can be visualized using comparative genome hybridization. Further diversification of FISH application will result from new ultrasensitive detection techniques.