Non- or minimally invasive prenatal diagnostic tests on maternal blood samples or transcervical cells

The prevention of thalassemia

The thalassemias are among the most common inherited diseases worldwide, affecting individuals originating from the Mediterranean area, Middle East, Transcaucasia, Central Asia, Indian subcontinent, and Southeast Asia. As the diseases require long-term care, prevention of the homozygous state constitutes a major armament in the management. This article discusses the major prevention programs that are set up in many countries in Europe, Asia, and Australia, often drawing from the experience in Sardinia. These comprehensive programs involve carrier detections, molecular diagnostics, genetic counseling, and prenatal diagnosis. Variability of clinical severity can be attributable to interactions with α-thalassemia and mutations that increase fetal productions. Special methods that are currently quite expensive and not widely applicable are preimplantation and preconception diagnosis. The recent successful studies of fetal DNA in maternal plasma may allow future prenatal diagnosis that is noninvasive for the fetus.

Use of the Quantitative Fluorescent-PCR Assay in the Study of Fetal DNA from Micromanipulated Transcervical Samples

AIM

The purpose of this study was to evaluate the validity of the combined use of micromanipulation and quantitative fluorescent (QF)-PCR assay for the identification of fetal elements in transcervical cell (TCC) samples collected in early pregnancy.

METHODS

TCC samples were obtained by intrauterine lavage (IUL) in 113 pregnant women who were between 7 and 12 weeks pregnant before termination of pregnancy. All IUL samples were screened under an inverted microscope, at which time the isolation of fetal cells by micromanipulation was attempted. QF-PCR assay, using 9 small tandem repeat (STR) markers for chromosomes 13, 18, 21, X, and Y, was performed in all specimens to identify fetal cells in TCC samples and the corresponding placental tissue and blood specimens. TCC samples from male fetuses in which either the micromanipulation or QF-PCR analysis were unsuccessful, were studied with fluorescent in situ hybridization (FISH), using probes for X and Y chromosomes.

RESULTS

Isolation of supposed fetal material from IUL samples was carried out by means of micromanipulation in 93 cases (82.3%), where discernible chorionic villous filaments or cell clumps of probable trophoblastic origin were present. The QF-PCR analysis was performed in all 93 IUL samples and paternal peaks could be documented in 88 cases (94.6%) thus confirming the presence of fetal cells. Thirteen cases negative to micromanipulation and derived from male fetuses and four male cases not informative with QF-PCR analysis, after micromanipulation, were then tested with FISH assay using probes for sexual chromosomes. In six samples, rare (2-3%) male fetal cells were detected. Considering the combined results obtained from QF-PCR and FISH assays, the overall fetal sexing was correct in 83.2% of cases (94 of 113).

CONCLUSION

This study provides evidence that fetal cells are present in a high proportion of IUL samples. Micromanipulation appears to be an extremely efficient method for the isolation of trophoblastic elements. This study also confirms the potential of IUL as a possible alternative to the traditional prenatal diagnostic procedures for the recovery of fetal cells in precocious stage of gestation, and validates the combination of the isolation of such fetal elements by means of micromanipulation and analysis with the QF-PCR assay for the identification of the most frequent prenatal chromosomal aneuploidies.

Detection of fetal cells present in transcervical samples

In 1971 Shettles postulated that, during pregnancy, chorionic cellular elements from degenerating villi were shed into the endocervical canal and could be analysed to assess fetal sex. Accordingly, he retrieved transcervical cells (TCC's) with cotton swabs and tested them for the presence of the Y chromosome using a fluorescent dye (quinacrine mustard). At the time of publishing his note, he had correctly diagnosed the sex of 10 fetuses in 18 pregnancies investigated.

The presence of trophoblastic cells in intrauterine lavage samples: lack of correlation with maternal and obstetric characteristics

OBJECTIVES

To investigate the correlation between maternal, obstetric and sample characteristics and the quality (i.e. yield of trophoblastic cells) of intrauterine lavage (IUL) samples.

METHODS

We collected 202 IUL samples from women scheduled for first trimester termination of pregnancy (TOP). Trophoblastic cells were isolated from IUL samples and used for DNA analysis by a multiplex quantitative fluorescent polymerase chain reaction (QF-PCR) assay. A multivariate logistic regression analysis was performed, and a p<0.05 was considered statistically significant.

RESULTS

The presence of trophoblastic cells in IUL samples was documented in 151/202 cases (74.7%). Blood contamination of IULs was the only characteristic to positively correlate with the presence of trophoblasts (p=0.039; OR: 1.99; 95% CI: 1.03-3.82).

CONCLUSIONS

The correlation between the presence of contaminating blood and trophoblastic cells would indirectly confirm the hypothesis that IUL might act as a mini-CVS. The high yield rate of trophoblasts irrespective of maternal characteristics and past obstetric history would support the clinical use of this sampling technique, provided that its safety is clearly defined.

Comparison of two techniques for transcervical cell sampling performed in the same study population

OBJECTIVES

The aim of this study was to evaluate and compare the presence of fetal cells in transcervical cell (TCC) samples collected in the first trimester of pregnancy by two different procedures [mucus collection and intrauterine lavage (IUL)], performed consecutively in the same subjects scheduled for elective termination of pregnancy (TOP).

METHODS

A total of 126 mucus/IUL sample pairs were retrieved from pregnant women immediately before TOP at a gestational age ranging from 7 to 12 weeks; at termination, samples of placental tissue were collected in all cases. All mucus samples were analysed by a polymerase chain reaction (PCR) assay and, in a subset of experiments involving 56 specimens, also by fluorescence in situ hybridization (FISH) procedure. IULs were divided in two aliquots, one for PCR analysis and one for the preparation of FISH slides. All placental tissue samples obtained at termination were analysed by FISH for fetal sexing. The PCR assay for fetal sex determination was performed by using, in a multiplex reaction, primers for SRY (Y chromosome sex-determining region, 738 bp) and HUMARA (human androgen receptor on the X chromosome, 280 bp) genes. The FISH analysis was carried out using direct-labelled commercial probes for X chromosome alpha-satellite (DXZ1, Xp11.1-q11.1, spectrum green) and Y chromosome alpha-satellite (DYZ3, Yp11.1-q11.1, spectrum orange) regions.

RESULTS

In samples from known male pregnancies (n = 67), full concordance between IUL and mucus results could be found in 11 cases (16.4%); in 41 cases, Y chromosome material was detected by FISH (n = 2), by PCR (n = 5) or both (n = 34) in IUL samples, but not in the corresponding mucus samples. Y chromosome material was not documented in 10 mucus/IUL sample pairs. In 5 cases, the FISH (n = 2), the PCR (n = 1) or both (n = 2) failed to detect Y chromosome material in IULs, which was detected, however, by PCR in the corresponding mucus samples. Overall, correct sex prediction was achieved in 55/67 IULs (82%) and in 16/67 (23.9%) mucus samples from male pregnancies. In samples from known female pregnancies (n = 56), full concordance between results of IUL/mucus pairs and those on placental samples could be found in 53 cases (94.6%); in 3 cases, Y chromosome material was documented by PCR in mucus samples, but not in the corresponding IULs. Correct sex prediction was therefore achieved in 56/56 IULs (100%) and in 53/56 (94.6%) mucus samples from female pregnancies.

CONCLUSION

This study provides evidence that, among TCC sampling techniques, IUL, but not mucus collection, can yield fetal cells in a constant and reliable fashion, which is a basic prerequisite for possible clinical usage. This suggestion had already emerged from some previous investigations but, owing to the study design, differences in study populations can no longer be used to explain the very different and sometimes-conflicting results reported in earlier studies.

Detection of fetal DNA in the peritoneal cavity during pregnancy

There is increasing evidence that fetal cells are commonly shed toward the cervix and in maternal circulation during pregnancy. In this study, a sample of peritoneal fluid was retrieved from a primigravida at 12 weeks' gestation undergoing urgent intervention for the torsion of an adnexal mass; the sample was then analysed by a polymerase chain reaction (PCR) assay using primers for X- and Y-chromosome specific sequences, and Y-derived sequences were identified. The course of pregnancy was then uneventful until term, when the patient delivered a male fetus, thus, supporting the hypothesis of a fetal origin for the Y-derived sequences detected in the peritoneal fluid. Further studies are required in order to confirm these findings and precisely define the origin of these sequences; however, this report seems to provide further evidence of the spreading of fetal cells during gestation and addresses relevant issues as to the possibility of collecting these cells by culdocentesis and intraperitoneal lavage for prenatal diagnosis.

Fetal cells in cervical mucus in the first trimester of pregnancy

OBJECTIVES

The aim of this study was to first evaluate the presence of fetal cells in cervical mucus samples collected in the first trimester of pregnancy and then to compare different laboratory methods for the detection of these cells.

METHODS

Mucus samples were collected by using a cytobrush before termination of pregnancy (TOP) from 143 pregnant women between 7 and 12 weeks of gestation. None of the women had undergone an invasive diagnostic procedure prior to cervical mucus sampling. Samples of placental tissue were collected from each patient at TOP. Slides from each sample were first observed under an inverted microscope to detect possible sperm contamination. In the first part of our experiments, 40 mucus samples were treated with a mucolytic solution containing N-acetylcysteine (AC) and were analysed by a polymerase chain reaction (PCR) assay. The second series, consisting of 71 mucus samples, was treated with a mucolytic solution containing dithiothreitol (DTT): all 71 samples were analysed by a PCR-based assay, and an aliquot for fluorescent in situ hybridisation (FISH) analysis was also obtained from 48 out of 71 samples. In the third part of our experiments, performed on 32 mucus samples, mucus trapped on the cytobrush was directly spread on two slides for FISH analysis without any mucolytic treatment. All placental tissue samples obtained at termination were analysed by FISH for fetal sexing.

RESULTS

Overall, the use of PCR-based or FISH analyses on 143 mucus samples resulted in correct sex prediction in 92/143 (64.3%) samples [20/66 (30.3%) cases from known male pregnancies and 72/77 (93.5%) cases from known female pregnancies]. In the AC group, Y-derived sequences were found in 7/23 samples (30.4%) from known male pregnancies and in 1/17 cases from known female pregnancies, with an overall correct sex prediction in 23/40 cases (57.5%). In the DTT group, Y-derived sequences could be amplified in 10/30 samples (33.3%) from known male pregnancies and in 4/41 cases from known female pregnancies, with an overall correct sex prediction in 47/71 cases (66.2%). In the DTT samples analysed by FISH, nuclei bearing XY signals were detected in 5/26 (19.2%) cases from known male pregnancies and in none from female pregnancies, the rate of correct sex prediction being 56.2% (27/48). On untreated mucus samples analysed by FISH, nuclei with XY signals were documented in 3/13 (23%) samples from male conceptuses and in none from known female pregnancies, with an overall correct sex prediction in 22/32 cases (68.7%).

CONCLUSION

Fetal cells were not detected in a constant and reliable fashion in cervical mucus samples collected in the first trimester of pregnancy. The detection rate was poorly influenced by the use of different laboratory methods. This sampling technique cannot be regarded as a promising tool towards minimally invasive prenatal diagnosis.

Strategies for the isolation and detection of fetal cells in transcervical samples

OBJECTIVE

The aim of the study was to evaluate the detection of fetal cells from transcervical samples, collected in early pregnancy, by means of different molecular techniques. The value of the isolation of trophoblasts using an inverted microscope, also referred to as micromanipulation, is discussed.

METHODS

All the 89 specimens were obtained by intrauterine lavages before termination of pregnancy (TOP), between 7 and 12 weeks of gestation. Micromanipulation was carried out in a subgroup of 57 for the isolation of fetal material. Fetal sexing was achieved by FISH (fluorescent in situ hybridisation) using fluorescently labelled probes for X and Y chromosomes and by polymerase chain reaction (PCR). Male samples were also investigated for aneuploidy of the chromosome 21. Quantitative fluorescent (QF)-PCR using two short tandem repeat (STR) markers for chromosome 21 was carried out in 26 micromanipulated samples.

RESULTS

FISH analysis revealed that 45/89 placental samples derived from pregnancies with male fetuses. Correct sexing of the lavage samples from male pregnancies was achieved in 41/45 (91%) using dual-FISH technique, and in 43/45 (95.5%) with PCR. All the samples derived from male pregnancies tested for chromosome 21 were normal. From 57 samples subjected to micromanipulation, 51 (89.5%) showed discernible chorionic villous filaments or cell clumps of possible trophoblastic origin. One case of tetraploidy and two cases of monosomy were recorded. The rate of fetal cells, in the non-micromanipulated samples, was between 4% and 97% (mean 54.3%). In micromanipulated specimens, maternal contaminant cells were absent or extremely rare (1-2%). The efficiency of the QF-PCR analysis in detecting paternal peaks in all lavage samples was only 61.5%.

CONCLUSION

The present study confirms the presence of fetal cells in a very high proportion of both whole and micromanipulated intrauterine lavage samples. The isolation of trophoblastic elements can be achieved in most cases by micromanipulation. FISH and PCR techniques allowed the analysis of the most common fetal aneuploidies, confirming the power of this minimally invasive method.

Detection of fetal cells in intrauterine lavage samples collected in the first trimester of pregnancy

OBJECTIVES

The aim of the present study was first to evaluate the presence of fetal cells in transcervical cell (TCC) samples collected by intrauterine lavage in the first trimester of pregnancy, and then to compare different methods for the detection of these cells.

METHODS

TCC samples were collected by intrauterine lavage before termination of pregnancy (TOP) from 81 pregnant women between 7 and 12 weeks of gestation. Samples of placental tissue were collected from each patient at TOP, whereas maternal peripheral blood samples were obtained in 57 cases. DNA extracted from 81 lavage and the corresponding placental samples was amplified by a polymerase chain reaction (PCR) assay using primers for SRY and HUMARA genes. All 81 lavage samples were also analysed by fluorescent in situ hybridisation (FISH) using direct-labelled probes for X chromosome alpha-satellite (DXZ1, Xp11.1-q11.1) and Y chromosome alpha-satellite (DYZ3, Yp11.1-q11.1) regions. In 57 cases, a quantitative fluorescent (QF) PCR assay, involving the use of two small tandem repeat (STR) markers (D21S11, D21S14.11) specific to chromosome 21 was employed to analyse DNA extracted from placental tissue, lavage and maternal blood samples.

RESULTS

PCR analysis revealed that 40/81 placental samples were from male pregnancies. Correct sexing was achieved with the PCR technique in 30/40 (75%) lavage samples retrieved from pregnant women with male conceptuses and in all 41 (100%) samples collected from pregnancies with female fetuses. With the FISH analysis, nuclei bearing X and Y signals were observed in 32/40 cases (80%) from known male pregnancies, the rate of fetal cells ranging between 2% and 95%, whereas nuclei showing X and Y signals were not detected in any of the 41 lavage samples from known female pregnancies. Paternal peaks were present in 30/57 (52.6%) lavage samples tested by QF-PCR.

CONCLUSION

The results suggest that fetal cells can be found, at a significant rate, in a very high proportion of intrauterine lavage samples. Therefore, this sampling technique can be regarded as a promising tool towards minimally invasive prenatal diagnosis. The FISH and PCR methods showed a similar efficiency in detecting fetal cells.

Fetal cells in the uterine cervix: a source for early non-invasive prenatal diagnosis

Various non-invasive techniques for prenatal diagnosis have been under investigation. We evaluated the success of fetal sexing using a non-invasive technique for obtaining fetal cells, uterine cervix brushing, in combination with FISH. Thirty pregnant women who completed between 6 and 10 weeks of gestation and who were scheduled to undergo pregnancy termination were included in the study. A Pap smear cytobrush was inserted through the external os to a maximum depth of 2 cm and removed while rotating it a full turn. The material that was caught on the brush was spread on four microscope slides. Two-color FISH was used for fetal sexing. Following pregnancy termination, a placental sample was used for full karyotyping. In 29/30 cases FISH diagnosis was confirmed by chromosomal analysis. The only male case in which a Y chromosome was not seen was from a pregnancy of 6 weeks 6 days gestational age. One case was mosaic of 46,XY/47,XXY (25%). In most cases (7/13) the Y chromosome was already identified in the first analyzed slide. With the use of a cytobrush fetal cells can be easily obtained for the purpose of prenatal diagnosis of chromosomal disorders.

Isolation of fetal cells from the maternal circulation: prospects for the non-invasive prenatal diagnosis

The research into non-invasive and invasive prenatal diagnostic techniques developed almost in parallel. On the one hand the need was arising to ensure the birth of normal progeny in all cases, while on the other, it was not possible to eliminate the abortion risks connected with the invasiveness of amniocentesis (risk of abortion 1/200), chorion villi sampling, (risk of abortion 2%) and funicolocentesis (risk of abortion 3-4%). One of the first researchers in the non-invasive field was Adinolfi who published the earliest data in 1974 on the possibility of detecting three types of fetal cells in the maternal circulation using flow cytometry. Adinolfi suggested the possibility of using fetal cells present in the maternal circulation for prenatal diagnosis of chromosome or biochemical anomalies. Our review takes into consideration the latest methodological and technical progress in relation to the study of fetal cells in maternal circulation, without considering cells present in the endocervical canal where from the 8th week of pregnancy it is only possible to obtain trophoblast cells. This technique has since been abandoned due to the scarcity of cellular material available, the greater risk of contamination by cells of maternal origin, and also because the recovery of the cells is unpredictable, despite their potential use for the early non-invasive diagnosis of sex. The following issues are addressed in this review: the characterization of the fetal cell types present in the maternal circulation, the methods of their separation and enrichment, and the methods of genetic diagnostics applied.

[Detection of fetal cells in maternal blood: myth or reality?]

Fetal cells exist in maternal blood and can be utilized for prenatal diagnosis. These cells are present from the sixth week of gestation, with frequency increasing as gestation advances, to many years after the birth. Enrichment of trophoblast cells, erythroblasts and lymphocytes was performed with various density gradient techniques and either magnetic activated or fluorescent activated sorting techniques. The abnormalities were detected by fluorescent in-situ hybridation (FISH) with chromosome-specific DNA probes for the detection of trisomy 21, trisomy 18, Klinefelter syndrome 47 XXY, or by polymerase chain reaction (PCR) for the detection of fetal sex, certain Mendelian disorders (as beta-globin mutations), HLA polymorphisms and fetal Rhesus D blood type. However others studies were necessary to determine the sensitivity and specificity of this technique as a noninvasive alternative to conventional methods of prenatal cytogenetic diagnosis.

Non-invasive early prenatal diagnosis using fluorescent in situ hybridization on transcervical cells: comparison of two different methods for retrieval

OBJECTIVE

We compared the efficiencies of uterine and endocervical lavage to retrieve fetal cells from first trimester pregnancies for further analysis with fluorescent in situ hybridization (FISH).

STUDY DESIGN

Transcervical cell (TCC) samples were collected at 7-10 weeks of gestations by uterine lavage (13 women) and by endocervical lavage (12 women) who were scheduled for volunteer termination of pregnancy. A sample of placenta was also obtained for cytogenetic analysis to confirm the sex or genotype in the end of the procedure. FISH was performed using probes for the chromosomes 18, X and Y in a three color hybridization protocol. The statistical analysis included chi(2)-analysis, and t-test.

RESULTS

Sufficient cells were obtained in 12 of the 13 (92.3%) in uterine lavage and 10 of the 12 (83.3%) in endocervical lavage group for FISH procedures for fetal sex prediction. The mean success rate of signal detection for FISH procedure was 91.7% (range 83-97%). Fetal sex was correctly predicted in 11 of 12 (91.6%) with uterine lavage and 8 of 10 (80.0%) in endocervical lavage and the difference was statistically insignificant.

CONCLUSION

This study demonstrated that there are available cells of fetal origin in the lower part of the uterus and these cells may be collected successfully as early as 7 weeks of the gestation. In addition, our results show that endocervical lavage method is as effective as uterine lavage. FISH has been successfully used to detect status of aneuploidy and sex of the fetus from TCC.

Transcervical sampling as a means of detection of fetal cells during the first trimester of pregnancy

OBJECTIVE

Our aim was to evaluate the detection of fetal cells from transcervical samples by means of fluorescence in situ hybridization analysis.

STUDY DESIGN

Forty-seven women undergoing first-trimester termination of pregnancy were recruited for transcervical sampling and 16 were recruited for endocervical mucus aspiration. Subjects were asked to assess the discomfort of the procedure. Fluorescence in situ hybridization analyses were performed with X and Y chromosome-specific probes. Results were compared with those of conventional chromosomal analysis.

RESULTS

Male signals (XY) were observed in 19 of 25 male fetuses (76%), and female signals (XX) were observed in 21 of 22 female fetuses. There was a significant variation between operators in cell retrieval. With mucus aspiration only 37.5% of male fetuses were correctly identified. The subjects did not find the procedure uncomfortable and reported that it was comparable to having a cervical smear taken.

CONCLUSIONS

Transcervical irrigation correctly identified the sex of 76% of male fetuses, but it still has considerable operator variability. This variability might be reduced by improved catheter design.

Transcervical cells and the prenatal diagnosis of haemoglobin (Hb) mutations

Prenatal diagnoses of haemoglobin (Hb) mutations were performed using transcervical cells, retrieved by aspiration from the endocervical canal of ten selected pregnant women at about 10 weeks of gestation, prior to chorionic villus sampling (CVS). Both parents were carriers of haemoglobinopathies (thalassaemia or HbS). Clumps of fetal cells were isolated by micromanipulation under an inverted microscope and aliquots of the extracted DNA tested separately for the presence of paternally derived chromosome markers and Hb mutations by quantitative fluorescent polymerase chain reaction (PCR). The correct prenatal diagnosis of Hb diseases, using selected single clumps of trophoblastic cellular elements free of maternal contaminating cells, was achieved in six out of ten cases.

Syncytiotrophoblastic fragments in first-trimester decidual veins: evidence of placental perfusion by the maternal circulation early in pregnancy

OBJECTIVE

To determine whether maternal placental perfusion occurs in the first trimester, this study compared veins in endometrium with those in decidua. We hypothesize that veins draining the placenta become dilated and contain syncytiotrophoblastic fragments.

STUDY DESIGN

Normal late-secretory endometrial biopsy specimens (n = 10) were compared with elective abortion decidua at 7 to 11 weeks (n = 100). Tissue sections were processed by routine staining and immunohistochemical studies. The cross sections of veins and glands were counted in 25 decidual biopsy specimens, and the number of syncytiotrophoblastic fragments in veins or glands was determined. Statistical significance by chi(2) or linear regression analysis was P <.05.

RESULTS

All sets of decidua had dilated veins; no secretory endometrium did. Intravenous syncytiotrophoblastic fragments were seen in 91 of 100 sets of decidua. There were more syncytial elements in veins (572/6845, 8.4%) than in glands (13/23,310, 0.06%) (P <.001).

CONCLUSION

Decidual veins were distended and contained syncytiotrophoblastic fragments, consistent with maternal intervillous perfusion in the first trimester.

Prenatal detection of Hb mutations using transcervical cells

Prenatal diagnoses were performed on six selected pairs of parents known to be carriers of Hb mutations by testing transcervical cells (TCCs) retrieved, prior to chorionic villus sampling (CVS), by aspiration of the cervical mucus from the pregnant mothers at 10-12 weeks of gestation. A concordance between the results of testing chorionic villus cells and isolated clumps of trophoblastic cellular elements was observed in four of the six cases.

Frequency of Fetal Cells in Sorted Subpopulations of Nucleated Erythroid and CD34+ Hematopoietic Progenitor Cells From Maternal Peripheral Blood

Fetal cells that circulate in maternal peripheral blood (PB) during pregnancy offer a potential source of nucleated fetal material for noninvasive prenatal diagnosis. Fluorescence-activated cell sorting was used to target two populations of fetal cells: nucleated erythroid cells (NECs; CD71/glycophorin-A+ CD45lo-int CD34−) and hematopoietic progenitor cells (CD34+ cells; CD34++ CD71/glycophorin-A− CD45int). Fetal cells were detected by fluorescence in situ hybridization (FISH) using directly conjugated chromosome X and Y probes in 65% (13 of 20) of the maternal PBs (fetal karyotype 46,XY). The frequency of fetal cells isolated from the NEC and CD34+ fractions was, respectively, 0 to 14 and 0 to 7 cells per 2 × 107 previously frozen maternal cells (≈20 mL of blood). In nonfrozen samples, the yield and recovery of fetal cells was moderately improved. Culturing the CD34+ sorted fractions in serum-free media with cytokines improved the quality of the FISH preparations and resulted in a slight expansion in detectable fetal cells. The frequency of fetal cells isolated from cultured CD34+ fractions was 0 to 35 and 0 to 93 cells per 2 × 107 previously frozen and nonfrozen maternal PB cells, respectively. These results document the isolation, characterization, and enumeration of fetal cells from the maternal periphery that appear to be present in most, but not all, samples analyzed.

Detection of cells of fetal origin from transcervical irrigations

Twenty-one women (age range 17-38 years) undergoing termination for social reasons in the first trimester were selected. Ultrasound determined the gestation and placental site. A commercially available flexible, sterile plastic tube was advanced to the level of the internal os. Five to eight millilitres of normal saline was injected and then gently aspirated into the tube. Chorionic villus sampling (CVS) or amniocentesis was subsequently performed for back-up sexing. Commercial X and Y probes were used simultaneously for fluorescence in situ hybridization (FISH) study of the cervical washing and back-up samples, XY signals were observed in 10 out of 12 male fetuses and 1 out of 4 female fetuses (false positive), indicating 81.3 per cent correct prediction. Four cervical washing samples did not provide enough cells for FISH. The frequency of cells showing XY signals varied from 3.6 to 47.8 per cent in male-predicted pregnancies. Placental-location, gestational age, or maternal age did not affect the successful retrieval of fetal cells. Trophoblast cells were obtained in a significant number (83 per cent) of pregnant women with male pregnancies by transcervical irrigation in the first trimester. This preliminary part of the study shows the presence of fetal cells in the transcervical samplings and the feasibility of FISH in detecting them; however, further studies are needed to isolate and purify fetal cells.

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 sickle cell anaemia and thalassaemia by analysis of fetal cells in maternal blood

Currently, amniocentesis, chorionic villus sampling (CVS) and fetal blood sampling are used to obtain fetal cells for genetic diagnosis. These invasive procedures pose a small but not negligible risk for the fetus. Efforts have been directed towards the enrichment of fetal cells, such as erythroblasts, from maternal blood and progress has been made in the diagnosis of some chromosomal disorders and in sex determinations. We now report the detection of point mutations in single gene disorders using this method of prenatal diagnosis by enriching fetal cells from maternal blood by magnetic cell sorting followed by isolation of pure fetal cells by microdissection. In two pregnancies at risk for sickle cell anaemia and beta-thalassaemia, we successfully identified the fetal genotypes. Thus, prenatal diagnosis of single gene disorders by recovering fetal cells from maternal circulation appears to be a feasible approach.