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

Noninvasive isolation of transcervical trophoblast cells for fetal identification

OBJECTIVE

To identify trophoblastic cells retrieved from the cervix at a gestational age (GA) of 5-9 weeks by a noninvasive modality in fetuses.

METHOD

Transcervical cells (TCCs) were noninvasively extracted by a cytobrush using the Papanicolaou sampling method. TCCs were immunostained with antihuman leukocyte antigen (HLA)-G and anticytokeratin (CK)-7 antibodies to identify trophoblastic cells. Maternal finger blood, gestational sacs, and 20 trophoblastic cells collected by a laser-guided microscopic single-cell capture system were examined and compared by short tandem repeat (STR) genotyping.

RESULTS

Forty-nine pregnant women with GA of 5-9 weeks and six nonpregnant healthy women were included in the study. Trophoblastic cells were identified in 37 (75.5%) TCC samples, among which 34 (69.4%) were eligible for STR genotyping analysis. No trophoblastic cells were identified in nonpregnant healthy women. The STR genotyping analyses revealed 24 female and 10 male fetuses. TCC trophoblastic cells exhibited the same STR profiles as gestational sac and maternal blood in all samples, which indicated that the TCC trophoblastic cells originated from fetuses.

CONCLUSION

This primary study validated that trophoblastic cells from TCCs at GA 5-9 weeks originated from the fetus. Further studies are needed to verify whether this method can be used for early noninvasive prenatal diagnosis and paternity testing.

Evaluation of an Improved Non-invasive Fetal Sex Determination in Haemophilia A Patients

BACKGROUND

Haemophilia A (HA) is the most severe sex-linked bleeding disorder that is characterized with non-controlled and often threatening Haemorrhage. Routine fetal sex determination in early pregnancy with Haemophilia is based on invasive procedures that can be dangerous to the mother and fetus.

AIM

The goal of this study is to present an improved assay for the non-invasive fetal sex determination using a Real-Time duplex PCR on the free fetal DNA (ffDNA) obtained from the maternal serum of the HA carriers.

MATERIALS AND METHODS

Blood samples were eventually collected from 23 pregnant HA carriers between the 8(th) and 12(th) weeks of gestation, and after amplification by duplex-PCR of the single copy of Y chromosome-specific sequence (SRY), the product was then subjected to Real-Time PCR analysis.

RESULTS

Data were compared with the outcome of chorionic villus sampling (CVS) and indicated that the SRY sequence was detected in 6 of 6 serum samples from male pregnancies and that sequence was absent in 9 samples where the fetus was female. The remaining samples determined without having the CVS positive samples.

CONCLUSION

We tried to develop a Real-Time duplex PCR for accurate diagnosis of fetal gender early in the pregnancy of HA carriers. This study has brought up two remarkable points, the first is the method's improvement with high specificity in sex determination, especially in screening of prenatal sex-linked disorders in male gender and the second is that fresh serum samples would be a good source for this purpose, advocated by similar studies carried out in this regard.

Detection of fetal cells from transcervical mucus plug before first-trimester termination of pregnancy by cytokeratin-7 immunohistochemistry

AIM

The presence of fetal cells in the endocervical mucus of pregnant women was first reported in 1971. The uterine cavity is patent during the first trimester prior to fusion of amnion and chorion. Fetal cells from degenerating chorion frondosum are theoretically shed into the uterine cavity between seven and 13 weeks' gestation and are trapped in the transcervical mucus; they can be identified by immunohistochemistry.

METHOD

Ninety-nine transcervical mucosal plugs from pregnant women of between 7 and 13 weeks before abortion were collected, fixed, embedded, sectioned and stained with monoclonal antibody of cytokeratin-7 (CK-7) by immunohistochemistry.

RESULT

The identification of trophoblasts on each slide was defined according to positive staining and histologically chorionic villous similarity under microscopic examination, using the following five categories: none (1), less than five single positive-stained cells per-section (2), more than five single positive-stained cells per-section (3), clumps of positive-stained cells (4), and histological-like intact or fragmented chorionic villi (5). From amongst 71 samples that qualified for analysis, individual slides were evaluated and categorized into three groups, with the following results: 32 (45.1%) fell into group 1 (category 1) denoting a negative result, 10 (14.1%) fell into group 2 (category 2) indicating a possible positive result and 29 (40.8%) fell into group 3 (any combination of categories 3-5) representing a positive result.

CONCLUSIONS

Fetal cells, identified by CK-7, can be found in more than 59.2% of the transcervical mucus in early pregnancy by use of a minimally invasive sampling method. Prenatal diagnosis of single-gene or chromosome disorders may be possible in the pregnant transcervical mucus by use of modern molecular methods and they deserve further study.

DNA identification of fetal cells isolated from cervical mucus: potential for early non-invasive prenatal diagnosis

OBJECTIVES

To develop a reliable method to isolate fetal cells for genetic diagnosis.

DESIGN

Aspiration of cervical mucus from pregnant women in the first trimester.

SETTING

Pregnant women were recruited before an elective termination of pregnancy.

POPULATION

Sixty pregnant women (7-10 weeks of gestation).

METHODS

Fetal cells were isolated from aspirated cervical mucus of pregnant women using a combination of enzymatic digestion, fluorescent immunohistochemistry, micromanipulation and single-cell DNA allelic profiling.

MAIN OUTCOME MEASURES

The isolation and identification of fetal cells.

RESULTS

The transformation of the tenacious cervical mucus into a single-cell suspension enabled the isolation and identification of fetal cells by fluorescent immunohistochemistry. Confirmation of fetal origin was accomplished by single-cell DNA allelic profiling alongside known maternal cells.

CONCLUSIONS

This novel non-invasive method is rapid and efficient with results attainable within 24 hours as early as seven weeks of gestation. The technique would offer earlier reassurance and the option of first trimester therapeutic abortions to both high and low risk pregnant women.

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.

[Contribution of genotyping for fetal sex determination in maternal serum for preimplantation genetic diagnosis of X-linked diseases]

OBJECTIVE

Couples with a risk of transmitting X-linked diseases included in a preimplantation genetic diagnosis (PGD) center need early and rapid fetal sex determination during pregnancy in two situations. The first situation corresponds to control of embryo sexing after PGD, the second one being that of couples in PGD program having a spontaneous pregnancy. Determination of fetal sex can be achieved by karyotyping using invasive procedures such as chorionic villus sampling (CVS), amniocentesis or cordocentesis and by non-invasive procedures such as ultrasound (US) examination. CVS is the earliest invasive procedure for fetal sex determination and molecular analysis of X-linked genetic disorders during the first trimester but it is associated with a risk of fetal loss. US allows reliable fetal sex determination only during the second trimester. Recently, reliable non-invasive fetal sex determination was realized by using SRY gene amplification in maternal serum.

PATIENTS AND METHODS

We report the prospective use of fetal sex determination in maternal serum in our PGD center. Management of pregnancies was performed using this non-invasive procedure in four cases of embryo sexing control and nine cases of spontaneous pregnancies in couples included in PGD program for X-linked diseases.

RESULTS

Fetal sex results using SRY gene amplification on maternal serum were in complete concordance with fetal sex observed by cytogenetic analysis or US examination, as well as at birth.

DISCUSSION AND CONCLUSION

This new strategy allowed rapid sex determination during the first trimester and permitted to avoid performing invasive procedures in nine pregnancies.

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.

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.

[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.

Fetal RHD genotyping in maternal serum during the first trimester of pregnancy

Fetal RHD genotype determination is useful in the management of sensitized RhD-negative pregnant women. It can be ascertained early during pregnancy by chorionic villus sampling (CVS) or amniocentesis. However, these procedures are invasive, resulting both in an increased risk of fetal loss and in an increased severity of immunization due to fetomaternal haemorrhage. A reliable determination of RHD genotype by fetal DNA analysis in maternal serum during the first trimester of pregnancy is reported in this study. One hundred and six sera from RhD-negative pregnant women were obtained during the first trimester of pregnancy. These sera were tested for the presence of RHD gene using a new real-time polymerase chain reaction assay and the results compared with those obtained later in pregnancy on amniotic fluid cells and by RHD serology of the new-born. All sera from women carrying a RhD-positive fetus (n = 62) gave positive results for RHD gene detection and sera from women carrying a RhD-negative fetus (n = 40) were negative. The high level of accuracy of fetal RHD genotyping obtained in this study could enable this technique to be offered on a routine basis for the management of RhD-negative patients during the first trimester of pregnancy.

Developments in laboratory techniques for prenatal diagnosis

Ongoing trends in prenatal diagnosis aim at early, rapid, and ideally noninvasive diagnosis as well as at the improvement of risk-screening for aneuploidy. Interphase-fluorescence in situ hybridization and quantitative fluorescence polymerase chain reaction are efficient tools for the rapid exclusion of selected aneuploidies in addition to the established direct preparation of chromosomes from chorionic villi. Interphase fluorescence in situ hybridization has also made possible the diagnosis of selected chromosome abnormalities in single cells (e.g. in preimplantation genetic diagnosis) or noninvasive diagnosis. More complex multicolor fluorescence in situ hybridization approaches are currently being evaluated. Single cell polymerase chain reaction is the key technique for the molecular diagnosis of a growing number of monogenic conditions before implantation or, still more experimental, in fetal cells retrieved from the maternal circulation. New sources for noninvasive diagnosis came into play such as fetal DNA or cell nuclei in maternal plasma. The combination of biochemical parameters in the maternal serum, namely free beta-human chorionic gonadotropin with pregnancy associated plasma protein A and sonographic markers, has already dramatically increased the sensitivity of risk screening in the first trimester of pregnancy.

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.