Fetal cells in cervical mucus in the first trimester of pregnancy

Trophoblast retrieval and isolation from the cervix: origins of cervical trophoblasts and their potential value for risk assessment of ongoing pregnancies

BACKGROUND

Early during human development, the trophoblast lineage differentiates to commence placentation. Where the placenta contacts the uterine decidua, extravillous trophoblast (EVT) cells differentiate and invade maternal tissues. EVT cells, identified by expression of HLA-G, invade into uterine blood vessels (endovascular EVT), as well as glands (endoglandular EVT), and open such luminal structures towards the intervillous space of the placenta. Endoglandular invasion diverts the contents of uterine glands to the intervillous space, while glands near the margin of the placenta that also contain endoglandular EVT cells open into the reproductive tract. Cells of the trophoblast lineage have thus been recovered from the uterine cavity and endocervical canal. An emerging non-invasive technology [trophoblast retrieval and isolation from the cervix (TRIC)] isolates and examines EVT cells residing in the cervix to explore their origin, biology and relationship to pregnancy and fetal status.

OBJECTIVE AND RATIONALE

This review explores the origins and possible uses of trophoblast cells obtained during ongoing pregnancies (weeks 5-20) by TRIC. We hypothesize that endoglandular EVT cells at the margins of the expanding placenta enter the uterine cavity and are carried together with uterine secretion products to the cervix where they can be retrieved from a Papanicolaou (Pap) smear. The advantages of TRIC for investigation of human placentation and prenatal testing will be considered. Evidence from the literature, and from archived in utero placental histological sections, is presented to support these hypotheses.

SEARCH METHODS

We used 52 out of 80 publications that appeared between 1966 and 2017 and were found by searching the PubMed and Google Scholar databases. The studies described trophoblast invasion of uterine vessels and glands, as well as trophoblast cells residing in the reproductive tract. This was supplemented with literature on human placental health and disease.

OUTCOMES

The literature describes a variety of invasive routes taken by EVT cells at the fetal-maternal interface that could displace them into the reproductive tract. Since the 1970s, investigators have attempted to recover trophoblast cells from the uterus or cervix for prenatal diagnostics. Trophoblast cells from Pap smears obtained at 5-20 weeks of gestation have been purified (>95% β-hCG positive) by immunomagnetic isolation with nanoparticles linked to anti-HLA-G (TRIC). The isolated cells contain the fetal genome, and have an EVT-like expression profile. Similar EVT-like cells appear in the lumen of uterine glands and can be observed entering the uterine cavity along the margins of the placenta, suggesting that they are the primary source of cervical trophoblast cells. Cells isolated by TRIC can be used to accurately genotype the embryo/fetus by targeted next-generation sequencing. Biomarker protein expression quantified in cervical trophoblast cells after TRIC correlates with subsequent pregnancy loss, pre-eclampsia and fetal growth restriction. A key remaining question is the degree to which EVT cells in the cervix might differ from those in the basal plate and placental bed.

WIDER IMPLICATIONS

TRIC could one day provide a method of risk assessment for maternal and fetal disease, and reveal molecular pathways disrupted during the first trimester in EVT cells associated with placental maldevelopment. As perinatal interventions emerge for pregnancy disorders and inherited congenital disorders, TRIC could provide a key diagnostic tool for personalized precision medicine in obstetrics.

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.

Endoreduplication in cervical trophoblast cells from normal pregnancies

OBJECTIVE

Fetal cells represented by extravillous trophoblasts (EVT) obtained from the cervix by a minimally invasive procedure are important for prenatal diagnosis in early pregnancies. Endoreduplication is a duplication of chromosomes without mitosis, leading to polyploidy that might represent increased cellular metabolic activity. In this study, we estimated the normal prevalence of polyploid trophoblasts exfoliated to the cervix between 5 and 13 weeks of gestation.

METHODS

Cervical samples were obtained by cytobrush, between 5 and 13 weeks of gestation from 36 randomly selected, singleton pregnancies. FISH was done with X, Y and two 21 probes.

RESULTS

We diagnosed 21 pregnancies with female and 15 pregnancies with male fetal karyotypes. A mean of 15.2 (0.02%) tetraploid cells were found in pregnancies with a female fetus and a mean of 2.0 (0.003%) tetraploid cells were found in pregnancies with a male fetus. The tetraploid cells (endoreduplicated trophoblasts) were two to three times larger than the normal cells usually seen in the cervix.

CONCLUSIONS

Extravillus trophoblasts tend to form endoreduplication to the ploidy level of 4c-8c of DNA. Those cells may represent a typical phenomenon in the growing placenta. Extravillus trophoblasts from female fetuses tend to form higher rates of endoreduplication.

Transcervical retrieval of fetal cells in the practice of modern medicine: a review of the current literature and future direction

OBJECTIVE

To review published methods for transcervical collection of fetal cells and to assess the potential of this approach for application in prenatal diagnosis.

MAIN OUTCOME MEASURE(S)

Retrospective analysis of efforts at prenatal diagnosis with trophoblast cells shed into the lower uterine pole that accumulate within the cervical mucus at the level of the internal os.

RESULT(S)

Minimally invasive techniques that include cervical mucus aspiration, cervical swabbing, and cervical or intrauterine lavage can be used to retrieve trophoblast cells during the first trimester for diagnostic purposes, including for prenatal genetic analysis. Fetal cells have been identified in these specimens with success rates that vary from 40% to 90%. The disparity in reported success rates can be a function of gestational age, collection method, operator variability, detection sensitivity, or pregnancy status. Molecular approaches have been devised to determine fetal sex and identify aneuploidies. Antibody markers have proven useful to select trophoblast cells for genetic analysis and to demonstrate that the abundance of recoverable fetal cells diminishes in abnormal gestations, such as in ectopic pregnancy or blighted ovum.

CONCLUSION(S)

Transcervical collection of fetal cells offers several avenues for prenatal diagnosis that with further refinement could one day provide valuable information for the management of ongoing pregnancies.

Retrieval of trophoblast cells from the cervical canal for prediction of abnormal pregnancy: a pilot study

BACKGROUND

Fetal cells are shed from the regressing chorionic villi and it is possible to retrieve extravillous cytotrophoblast cells by transcervical sampling. The abundance of trophoblast cells in transcervical samples suggests that this non-invasive approach could distinguish between normal and abnormal pregnancies, such as an ectopic pregnancy (EP) and blighted ovum (BO). We aim to identify and quantify fetal trophoblast cells in the cervical canal during the first trimester to assess their usefulness to predict an abnormal pregnancy.

METHODS

Patients, age 18-45, presenting with a normal intrauterine pregnancy (IUP; n = 37), diagnosis of EP (n = 10) or BO (n = 5) were enrolled for collection of transcervical specimens using a cytobrush and fixative rinse. Non-pregnant, nulliparous women (n = 7) were included as negative controls. Cells were cleared of mucus by acidification, prepared on microscope slides and labeled with a monoclonal antibody recognizing the trophoblast marker, human leukocyte antigen (HLA)-G. HLA-G positive and negative cells were counted to calculate the ratio of trophoblast cells to total cervical cells.

RESULTS

Trophoblast cells were observed in 35/37 normal IUP, 6/10 EP and 4/5 BO specimens. The average frequency of HLA-G positive cells in the normal IUP cervical samples was approximately 1 in 2000, which was 4-fold higher than samples from patients with EP or BO (P < 0.001). Receiver operating characteristic analysis showed that EP and BO pregnancies were distinguishable from normal pregnancies with 93% sensitivity, 95% specificity, 97% positive predictive value and 87% negative predictive value.

CONCLUSIONS

This pilot study presents evidence that trophoblast cells can be reliably obtained and identified among cervical cells in the first trimester by immunohistochemical staining for HLA-G, and suggests for the first time that abnormal pregnancies may be predictable based on the abundance of trophoblast cells in the cervical canal.

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.

Prenatal diagnosis of common aneuploidies in transcervical samples using quantitative fluorescent-PCR analysis

AIM

The aim of this study was to test the feasibility of diagnosing common fetal chromosomal aneuploidies using quantitative fluorescent (QF)-PCR on transcervical cell (TCC) samples collected in the first trimester of pregnancy by means of intrauterine lavage (IUL).

METHODS

A total of 181 TCC samples were retrieved from pregnant women between 5 and 12 weeks of gestation, immediately before elective termination of pregnancy, at which time corresponding placental tissue and maternal blood specimens were also obtained. Isolation of trophoblastic cells by micromanipulation was attempted in all TCC samples. Micromanipulated specimens were analyzed by multiplex QF-PCR, including short tandem repeats for the chromosomes X, Y, 21, 18, and 13.

RESULTS

The micromanipulation was successful in 152 of 181 cases (84.8%) where chorionic villous filaments and/or cell clumps of seeming trophoblastic origin could be isolated. All 152 samples were tested by QF-PCR analysis and peaks of paternal origin could be documented in all cases. Two cases of trisomy 21 and two cases of monosomy X0 were detected by means of QF-PCR assay, in accordance with the results obtained in corresponding placental samples.

CONCLUSION

This study provides evidence that the use of multiplex QF-PCR amplification of selected microsatellites could be applied to micromanipulated TCC samples and in particular to IUL samples, which often contain trophoblastic cells, for the detection of chromosomal aneuploidies. The approach described in this study appears, therefore, a very promising tool toward non-invasive prenatal genetic diagnosis in the early stage of gestation.

Preliminary report: Correct diagnosis of sex in fetal cells isolated from cervical mucus during early pregnancy

The aim of this study was to determine the accuracy of sexing fetal cells isolated from cervical mucus. Immunopositive cells identified using a fetal-specific antibody were isolated and subjected to genetic analysis. Fetal sex was predicted in all 22 samples, as confirmed by analysis of the corresponding placental tissue. This study validates the accuracy of our test for sex diagnosis and confirms the ability to effectively recover and analyse fetal cells from the cervical mucus during early pregnancy.

Endocervical fetal trophoblast for prenatal genetic diagnosis

PURPOSE OF REVIEW

For over a decade, methods of first-trimester, noninvasive prenatal genetic diagnosis have been actively pursued by many investigators. Isolation of fetal trophoblast from endocervical specimens remains an attractive approach, given the greater numbers of fetal cells than in maternal blood and the better potential for fetal-cell identification based on markers specific for a single cell type (trophoblasts).

RECENT FINDINGS

Current studies demonstrate feasibility in identification and molecular analysis of fetal trophoblast cells for prenatal genetic testing. Sampling methods involving lavage, cytobrush, or aspiration of cervical specimens, however, have limitations in the recovery of trophoblasts.

SUMMARY

Clinical applications await further systematic studies to determine safety and accuracy in recovery.

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.

Invasive fetal testing

PURPOSE OF REVIEW

Research on prenatal diagnosis and invasive fetal testing has continued at a rapid pace. Several studies that will have a profound impact on the way prenatal care will be provided to pregnant women have been published in the literature during the last year. These publications will be reviewed and their impact described.

RECENT FINDINGS

The main areas of interest in the recent literature covered in this review are first-trimester screening for aneuploidy, recent information on loss rates due to amniocentesis and chorionic villus sampling, and current work on invasive fetal therapy.

SUMMARY

It appears that first-trimester screening is at least comparable if not superior in efficacy to second-trimester serum screening. This will be a test that will be utilized increasingly by both low and high-risk patients for aneuploidy. Of utility to a much smaller number of patients, invasive fetal therapy for meningomyelocele repair, twin-to-twin transfusion syndrome and fetal cardiac malformations is being evaluated in a scientifically more rigorous manner.