A simple alternative to amniocentesis?

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.

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.

A review of fluorescence in situ hybridization (FISH): current status and future prospects

Fluorescence in situ hybridization (FISH) is a powerful technique for detecting DNA or RNA sequences in cells, tissues and tumors. This molecular cytogenetic technique enables the localization of specific DNA sequences within interphase chromatin and metaphase chromosomes and the identification of both structural and numerical chromosome changes. FISH is quickly becoming one of the most extensively used cytochemical staining techniques owing to its sensitivity and versatility, and with the improvement of current technology and cost effectiveness, its use will surely continue to expand. Here we review the wide variety of current applications and future prospects of FISH technology.

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.

Non-invasive early prenatal molecular diagnosis using retrieved transcervical trophoblast cells

Fetal DNA was recovered from 17 of 39 (44%) transcervical cell (TCC) samples obtained between 7 and 9 weeks of gestation by endocervical canal flushing. Trophoblast retrieval was adequate for polymerase chain reaction (PCR) amplification of Y chromosome-specific DNA sequences and detection of paternal-specific microsatellite alleles. The fetal sex predicted by PCR in TCCs was confirmed in all cases by karyotype analysis of chorionic villi at 10 weeks of gestation. The absence of the disease-associated paternal alleles in TCC samples from two pregnancies at risk for spinal muscular atrophy and myotonic dystrophy predicted unaffected fetuses in agreement with subsequent results on chorionic villi and newborns' leukocytes. A trisomy 21 fetus was diagnosed in TCCs using fluorescent in situ hybridization (FISH) and semi-quantitative PCR analysis of superoxide dismutase-1 (SOD 1). Present experience indicates that TCC sampling is a promising technique for early prenatal monitoring of Mendelian disorders and chromosome aneuploidy.

Immunohistochemical characterization of cells retrieved by transcervical sampling in early pregnancy

Trophoblastic cells can be retrieved from the endocervix and the lower uterine segment in early pregnancy by aspiration or lavage (Rodeck et al., 1995). The feasibility of using this technique for prenatal diagnosis depends on how frequently fetal cells can be retrieved and whether such cells can be purified from the predominant maternal cell population. In this study, specimens retrieved from the lower uterine segment prior to elective first-trimester termination of pregnancy were examined histologically and characterized using a panel of monoclonal antibodies in an avidin-biotin-peroxidase technique. Lavage samples generally contained fewer cervical epithelial cells than aspirates. Syncytial fragments or cytotrophoblast were identified in 9 of 12 lavage samples but in only 4 of 10 aspirates. Trophoblast cells were reactive with various anti-trophoblast monoclonal antibodies but the trophoblast cells present displayed considerable antigenic heterogeneity. For positive selection of trophoblast cells from these samples, it is likely that the best yield will be achieved by using a panel of carefully characterized monoclonal antibodies directed against various villous and extravillous trophoblast populations.

Detection of fetal cells in transcervical samples and prenatal diagnosis of chromosomal abnormalities

Transcervical samples collected by lavage, aspiration, and cytobrush from women between 6 and 13 weeks of gestation were tested for the presence of fetal cells using fluorescence in situ hybridization (FISH) with probes for chromosomes X, Y, 1, and 21, and by polymerase chain reaction (PCR) amplification of DNA sequences derived from chromosomes X, Y, and 21. With a few exceptions, a good correlation was observed between the results of sexing the fetuses using FISH or PCR on transcervical cell (TCC) samples retrieved by lavage and those obtained by testing fetal (placental) tissue. In a comparative study between TCC samples collected by lavage or cytobrush, the sex of the fetus was correctly diagnosed by PCR amplification of a Y-derived DNA sequence. Variable results were observed with samples obtained by aspiration, mainly because this procedure was found to be more prone to failure to remove thick mucus without previous injection of physiological saline. Chromosome 21-derived small tandem repeats (STRs) of fetal origin were successfully detected in about 40 per cent of TCC samples recovered by lavage. Two cases of chromosomal abnormalities, one of trisomy 21 and one of triploidy, were detected in TCC samples in the course of our investigations.

Methods for the transcervical collection of fetal cells during the first trimester of pregnancy

Before termination of pregnancy, four techniques for retrieving fetal cells transcervically were investigated: uterine lavage, endocervical lavage, cytobrush and mucus aspiration. The yield of fetal cells in these samples was studied and found to be somewhat better after uterine lavage. A preliminary assessment of the safety of mucus aspiration was carried out before transcervical chorionic villus sampling (CVS) in continuing pregnancies. No difference in outcome to a control group having only CVS was found.

Molecular evidence of fetal-derived chromosome 21 markers (STRs) in transcervical samples

Transcervical cells (TCCs), collected by flushing or aspiration at 8-13 weeks of gestation, were analysed for the presence of fetal-derived DNA sequences. DNA extracted from maternal peripheral blood, TCC samples, and placental tissue was amplified by the polymerase chain reaction (PCR) to detect small tandem repeat (STR) markers specific to chromosome 21. STR products of fetal origin could be clearly observed in four TCC samples. TCC samples collected by flushing or aspiration were also analysed by fluorescent in situ hybridization (FISH) using X and Y probes simultaneously: 46,XY cells could be detected in all TCC samples obtained from mothers with male fetuses.