Chorionic villus sampling
Chorionic villus sampling (CVS) is an invasive prenatal diagnostic procedure performed between 10 and 13 weeks of gestation to detect fetal chromosomal abnormalities, genetic disorders, and certain congenital conditions by extracting a small sample of chorionic villi from the placenta.[1] The chorionic villi, finger-like projections of placental tissue sharing the same genetic material as the fetus, provide cells for cytogenetic analysis, fluorescence in situ hybridization (FISH), or molecular testing to identify conditions such as Down syndrome, cystic fibrosis, or Tay-Sachs disease.[1] CVS offers earlier results compared to amniocentesis, enabling timely decision-making on pregnancy continuation or preparation for neonatal care, though it carries a procedure-related risk of miscarriage estimated at 0.5% to 1%, higher than the background rate but supported by empirical data from large cohorts showing total fetal loss rates post-procedure around 0.7% to 2.9% depending on gestational timing and patient factors.[2][1][3] Developed in the late 1970s and refined through the 1980s, CVS emerged as a faster alternative to amniocentesis, with techniques evolving from transcervical to predominantly transabdominal approaches to minimize infection risks and improve safety.[1] Early adoption faced scrutiny over potential associations with limb reduction defects and oromandibular-limb hypogenesis syndrome, particularly in procedures before 10 weeks, but randomized trials and meta-analyses have since demonstrated no causal link beyond baseline risks, attributing early reports to confounding factors like selection bias or spontaneous loss of abnormal fetuses.[4][5] Despite these resolutions, CVS remains recommended for high-risk pregnancies identified via noninvasive screening, balancing diagnostic accuracy—approaching 99% for chromosomal detection—against empirical risks, with ongoing refinements in ultrasound guidance reducing complications.[1][6]Definition and Procedure
Overview and Mechanism
Chorionic villus sampling (CVS) is an invasive prenatal diagnostic procedure used to detect fetal chromosomal abnormalities and genetic disorders by sampling placental tissue. Performed typically between 10 and 13 weeks of gestation, CVS allows for earlier diagnosis compared to amniocentesis, which occurs later in pregnancy.[1][7] The mechanism relies on the collection of chorionic villi, which are vascular projections from the fetal chorion that form the fetal component of the placenta. These villi consist of trophoblastic cells surrounding a mesenchymal core, both derived from the fetus and thus containing identical genetic material to the developing embryo.[1][8] Sampling these cells provides a direct source for genetic analysis without directly accessing fetal fluids or tissues.[7] Laboratory analysis of the villus sample involves direct preparation of cytotrophoblast cells for rapid preliminary results or culturing mesenchymal core cells for more comprehensive testing, including karyotyping to identify aneuploidies, fluorescence in situ hybridization (FISH) for specific chromosomal issues, or polymerase chain reaction (PCR) for single-gene mutations. This enables detection of conditions such as trisomy 21, trisomy 18, or inherited disorders like Tay-Sachs disease.[1] The fetal origin of the cells ensures the genetic profile reflects the embryo's, though maternal cell contamination can occur and requires verification techniques like quantitative fluorescence PCR.[1]Techniques and Timing
Chorionic villus sampling is typically performed between 10 and 13 weeks of gestation to allow early detection of fetal genetic abnormalities while avoiding higher risks of congenital anomalies, such as limb reduction defects, associated with procedures before 10 weeks.[1][7][8] This window precedes the standard timing for amniocentesis, enabling faster decision-making for patients.[1] Two primary techniques are used: transcervical chorionic villus sampling (TC-CVS) and transabdominal chorionic villus sampling (TA-CVS), both requiring continuous ultrasound guidance for precise sampling of placental chorionic villi.[1][7] The selection depends on placental location, gestational age, and clinician preference; TA-CVS is often favored for its procedural simplicity in later first-trimester cases.[1][8] In TC-CVS, the patient is positioned in dorsal lithotomy, a speculum is inserted to expose the cervix, which is cleansed antiseptically, and a thin catheter or biopsy forceps is advanced through the cervical os to the chorion under ultrasound visualization; gentle suction or nibbling collects 10–30 mg of villous tissue.[1][7] This approach may cause mild cramping but carries a slightly elevated risk of infection compared to TA-CVS due to vaginal access.[1] TA-CVS involves the patient lying supine with the abdomen sterilized; an 18- or 20-gauge spinal needle is inserted transabdominally into the placenta, often after optional local anesthesia, and tissue is aspirated via syringe movements under real-time ultrasound.[1][8] This method is suitable for anterior or higher placentas and generally results in less discomfort from cervical manipulation.[1] Both techniques typically last 10–20 minutes, with samples immediately processed for cytogenetic analysis.[1][7]Historical Development
Origins and Early Trials
The concept of sampling chorionic villi for prenatal diagnosis emerged in the late 1960s, with Danish researcher Jan Mohr reporting the first attempt in 1968 using a transcervical approach with a 5 mm endoscope under direct vision for placental biopsy.[9][10] This method achieved a 96% success rate in obtaining samples but was associated with high complication rates, including bleeding, infection, and failed cell cultures, leading to its initial rejection as unsafe.[10] Further exploratory work in Scandinavia during the early 1970s demonstrated the feasibility of fetal chromosome analysis from transcervical placental biopsies, as reported by Swedish researchers Kullander and Sandahl alongside Danish investigator Hahnemann in 1973, though these were primarily conducted prior to elective terminations rather than for ongoing pregnancies.[10] The first documented successful prenatal diagnostic application occurred in 1975 at Tietung Hospital in Anshan, China, where blind aspiration via a 3 mm cannula was used for fetal sex determination in 100 patients between 8 and 12 weeks' gestation.[10][11] This trial yielded a 94% diagnostic accuracy rate but incurred a 6% error rate in sex prediction and a 4% fetal loss rate, highlighting early procedural risks without ultrasound guidance.[10] By 1980, Soviet researchers Kazy and colleagues introduced ultrasound-guided chorionic villus sampling (CVS) using biopsy forceps at 6-12 weeks' gestation for fetal sexing and enzyme assays, marking a shift toward real-time imaging to improve precision and reduce complications.[10] In 1983, independent advancements in Western Europe refined the transcervical technique under ultrasound guidance: British obstetrician Rodney Ward in London reported success rates of 67-96% with catheter aspiration, while Italian researchers Bruno Brambati and Giuseppe Simoni in Milan achieved similar outcomes, establishing CVS as a viable first-trimester alternative to mid-trimester amniocentesis despite ongoing concerns over maternal-fetal risks and mosaicism.[10][12] Early trials emphasized the procedure's potential for rapid cytogenetic analysis but underscored the need for larger studies to quantify procedure-related fetal loss, which initial data suggested exceeded that of amniocentesis by 1-2%.[11]Widespread Adoption
Chorionic villus sampling (CVS) transitioned from experimental trials to routine clinical use in the early 1980s, driven by its capacity for first-trimester diagnosis compared to second-trimester amniocentesis. Initial large-scale implementations occurred in Europe, with centers in Sweden and the United Kingdom reporting over 1,000 procedures by 1984, demonstrating procedural success rates exceeding 95% for obtaining adequate samples. In the United States, adoption accelerated following multicenter studies, such as the Golbus group's analysis of 1,000 cases in 1986, which established baseline safety data with a fetal loss rate of 3.8%.[10][10] By the late 1980s, CVS had become widely available internationally, supported by the World Health Organization's International Registry of CVS procedures, which tracked thousands of cases annually across participating centers. The technique's earlier gestational timing—typically 10 to 13 weeks—facilitated prompt decision-making for high-risk pregnancies, contributing to its uptake in advanced maternal age screening protocols. In the United States, by 1990, approximately 40% of pregnant women aged 35 years or older underwent either CVS or amniocentesis, reflecting CVS's integration into standard prenatal care for genetic risk assessment.[4][4] Adoption was further propelled by refinements in transabdominal approaches, which reduced infection risks associated with transcervical methods, leading to broader operator training and institutional offerings by the end of the decade. Professional guidelines from bodies like the American College of Obstetricians and Gynecologists implicitly endorsed CVS as a viable option in the early 1990s, though uptake varied by region due to varying access to ultrasound guidance. Despite this expansion, early 1990s reports of slightly elevated fetal loss rates—around 0.7% to 1% higher than amniocentesis—and rare associations with limb reduction defects prompted procedural adjustments, such as restricting sampling before 10 weeks, which tempered but did not reverse its established role.[13][14]Clinical Indications
Risk Factors for Testing
Chorionic villus sampling (CVS) is indicated for pregnancies with elevated risk of fetal chromosomal, genetic, or structural abnormalities, allowing for early diagnosis between 10 and 13 weeks of gestation.[1] These risk factors are identified through maternal history, screening tests, or imaging, prompting invasive diagnostic confirmation when noninvasive options like cell-free DNA testing yield inconclusive or high-risk results.[1] Guidelines from professional bodies emphasize offering CVS to individuals with specific profiles to balance diagnostic accuracy against procedural risks.[15] Advanced maternal age, typically 35 years or older at the time of delivery, constitutes a primary indication due to the exponential increase in aneuploidy risk, such as trisomy 21, with rates rising from about 1 in 1,250 at age 25 to 1 in 100 at age 40.[1] Advanced paternal age may also factor in, though evidence is less robust, as it correlates with de novo mutations in certain genetic disorders.[1] Similarly, a history of a prior child with structural birth defects, autosomal trisomy, or sex chromosome aneuploidy warrants CVS to assess recurrence risks, which can exceed baseline population rates by factors of 2-10 depending on the anomaly.[1][16] Abnormal prenatal screening results are frequent triggers, including positive noninvasive prenatal testing (NIPT) for aneuploidies, elevated risk on first-trimester combined screening (integrating nuchal translucency measurement, pregnancy-associated plasma protein-A, and human chorionic gonadotropin levels), or serum analyte disruptions indicating conditions like neural tube defects.[1] Ultrasound findings, such as increased nuchal translucency (≥3.5 mm), cystic hygroma, or early structural anomalies like holoprosencephaly, further elevate suspicion and justify CVS, as these markers predict chromosomal issues in 20-50% of cases.[1][16] Parental genetic factors represent targeted indications, particularly when one or both parents are carriers of balanced chromosomal rearrangements (e.g., translocations), increasing unbalanced offspring risk to 10-15%; or known carriers of single-gene disorders like Tay-Sachs disease, sickle cell anemia, or neurofibromatosis type 1, where Mendelian inheritance patterns predict affected probabilities of 25% or higher.[1] Parental mosaicism or aneuploidy, confirmed via prior cytogenetic analysis, also prompts testing to evaluate transmission potential.[1] Family history of heritable conditions, even without direct parental carrier status, may indicate CVS if linkage analysis or prior affected relatives suggest elevated fetal risk.[16]Targeted Genetic Conditions
Chorionic villus sampling (CVS) targets chromosomal aneuploidies and structural abnormalities detectable through cytogenetic analysis of placental tissue, which shares the fetus's genetic material. Common conditions include trisomy 21 (Down syndrome), trisomy 18 (Edwards syndrome), and trisomy 13 (Patau syndrome), with detection rates approaching 100% for non-mosaic whole-chromosome aneuploidies.[1][17] Sex chromosome abnormalities, such as monosomy X (Turner syndrome) and XXY (Klinefelter syndrome), as well as autosomal monosomies, are also identifiable.[18] Structural chromosomal variants, including deletions, duplications, translocations, and inversions, can be diagnosed via karyotyping or fluorescence in situ hybridization (FISH) on CVS samples, enabling early identification of syndromes like cri du chat (5p deletion).[1] These analyses provide definitive results earlier than amniocentesis, typically between 10 and 13 weeks gestation.[7] For monogenic disorders, molecular testing on CVS-derived DNA targets conditions with known mutations, such as cystic fibrosis (CFTR gene), Tay-Sachs disease (HEXA gene), sickle cell anemia (HBB gene), and spinal muscular atrophy (SMN1 gene), especially in cases of parental carrier status or family history.[19] Techniques like polymerase chain reaction (PCR) or next-generation sequencing confirm pathogenic variants, though detection depends on the disorder's genetic basis and assay specificity.[1] CVS does not screen for multifactorial or non-genetic birth defects, such as neural tube defects.[7]Diagnostic Process and Analysis
Sample Collection and Laboratory Methods
Chorionic villus sampling employs two principal techniques for obtaining placental tissue: the transcervical approach and the transabdominal approach, both guided by real-time ultrasound imaging and typically performed between 10 and 13 weeks of gestation to ensure accessibility of the chorionic villi.[1] The choice between methods depends on placental location, uterine anatomy, and operator preference, with transabdominal being more common in many settings due to lower infection risk.[1] In the transcervical method, the patient assumes a dorsal lithotomy position, facilitating insertion of a sterile speculum to expose and cleanse the cervix with antiseptic. A flexible catheter, often 3 to 4 French in diameter with an echogenic tip for ultrasound visualization, is gently advanced through the cervical os to the base of the chorionic villi. A syringe containing transport medium is attached, and negative pressure is applied to aspirate 10 to 30 milligrams of villous tissue, which is then detached and withdrawn. A tenaculum may stabilize the cervix, and biopsy forceps serve as an alternative for direct grasping in select cases.[1] [20] The transabdominal method positions the patient supine, with the abdomen sterilized using chlorhexidine or iodine solution under sterile drapes. An 18- or 20-gauge spinal needle is inserted percutaneously through the abdominal and uterine walls directly into the placental core, avoiding the amniotic cavity. Local anesthesia is optionally administered at the puncture site. A syringe with collection medium is connected after stylet removal, and tissue is procured by applying suction while rhythmically advancing and withdrawing the needle to shear off villi. This approach mirrors aspects of amniocentesis but targets placental rather than amniotic fluid sampling.[1] Following collection, the sample is promptly transferred to a sterile container with tissue culture medium, such as Ham's F-10 or RPMI 1640 supplemented with antibiotics, and transported to the laboratory at ambient temperature to preserve cell viability. Initial assessment confirms the presence of adequate fetal-derived chorionic villi, distinguishing them from maternal decidua via microscopic examination of finger-like projections.[1] [16] Laboratory processing begins with mechanical and enzymatic disaggregation of the villi to isolate trophoblast cells, minimizing maternal contamination through selective digestion and differential sedimentation. For rapid preliminary analysis, direct squash preparations of uncultured cytotrophoblasts enable fluorescence in situ hybridization (FISH) or quantitative fluorescence PCR, providing results for common aneuploidies (e.g., trisomies 13, 18, 21, sex chromosomes) within 24 to 48 hours, albeit with potential for lower resolution and higher mosaicism detection.[1] [21] Comprehensive evaluation involves short-term culture of mesenchymal core cells for 7 to 14 days in monolayer or flask systems, yielding metaphase spreads for G-banded karyotyping to identify chromosomal aberrations at 400-550 band resolution. Advanced techniques, including chromosomal microarray analysis (CMA) for copy number variants and single nucleotide polymorphism (SNP) arrays, detect submicroscopic deletions or duplications not visible by karyotype. Targeted molecular assays, such as polymerase chain reaction (PCR) for single-gene disorders (e.g., cystic fibrosis mutations), complement cytogenetic methods when clinically indicated. Cultured cell yields support multiple tests, with failure rates under 1% in experienced labs due to optimized protocols.[1] [16] [21]Interpretation of Results
Results from chorionic villus sampling (CVS) are interpreted through cytogenetic analysis of the chorionic villi, which provides a karyotype reflecting the fetal chromosomal constitution, typically completed within 1 to 2 weeks for full culture-based results, with rapid preliminary assessments via fluorescence in situ hybridization (FISH) or quantitative fluorescent polymerase chain reaction (QF-PCR) available in 2 to 4 days for common aneuploidies such as trisomies 21, 18, and 13.[1] A normal euploid karyotype, such as 46,XX or 46,XY, indicates no detectable major chromosomal abnormalities, correlating with a low likelihood of associated conditions like Down syndrome, though it does not exclude submicroscopic genetic variants, single-gene disorders, or environmentally induced birth defects.[16] [1] Abnormal findings reveal aneuploidies, structural chromosomal rearrangements, or deletions/duplications detectable by karyotyping or chromosomal microarray, with detection rates approaching 99% for non-mosaic whole-chromosome abnormalities larger than 5 to 20 Mb.[16] These results confirm fetal involvement in conditions like trisomy 21 (47,XX,+21), enabling informed clinical decisions, though balanced rearrangements may carry no phenotypic impact.[1] In high-risk pregnancies, chromosomal abnormalities appear in approximately 3% of CVS samples overall, rising to 21% in select cohorts with advanced maternal age or prior affected pregnancies.[16] [22] Mosaicism, observed in 1% to 2% of CVS analyses, presents interpretive challenges as it involves a mixture of normal and abnormal cells; confined placental mosaicism (CPM), where the abnormality is restricted to extraembryonic trophoblast or mesenchymal core, accounts for most cases and affects fetal karyotype in only about 10% of instances, potentially leading to false-positive interpretations without follow-up.[1] [23] True fetal mosaicism requires confirmation via amniocentesis, as CVS mosaicism correlates with risks like intrauterine growth restriction even in CPM cases.[1] [16] False-positive results are uncommon but stem from maternal cell contamination (rare in singleton pregnancies), culture artifacts mimicking mosaicism, or CPM; false negatives are minimal for targeted chromosomal issues but possible for low-level mosaicism or non-chromosomal anomalies.[1] [16] Interpretation mandates genetic counseling to convey uncertainties, with recommendations for serial ultrasounds, repeat invasive testing, or specialized care based on findings.[1]Risks and Complications
Maternal and Procedural Risks
Chorionic villus sampling (CVS) carries procedural risks primarily related to the invasive nature of sample collection via transcervical or transabdominal approaches, including potential for maternal vaginal spotting or light bleeding, which affects 10-30% of patients but typically resolves without intervention.[1] Cramping or discomfort during or immediately after the procedure occurs in a minority of cases, analogous to mild menstrual pain, and is managed conservatively.[24] Infection risk, such as endometritis or chorioamnionitis, remains low at less than 0.1% across large cohorts, attributable to sterile technique and antibiotic prophylaxis when indicated.[25] Amniotic fluid leakage or premature rupture of membranes is exceedingly rare, reported in fewer than 0.5% of procedures.[26] The procedure-related risk of miscarriage, defined as fetal loss before 24 weeks attributable to CVS rather than baseline pregnancy risk, is estimated at 0.22-0.31% based on systematic reviews comparing outcomes to unprobed pregnancies.[27] [28] This excess risk, derived from meta-analyses of over 13,000 CVS cases, shows no statistically significant elevation beyond background rates in some modern series, though earlier studies reported higher figures up to 1%.[29] [30] Transabdominal CVS may confer slightly lower complication rates than transcervical approaches due to reduced cervical trauma risk, with failure to obtain adequate sample occurring in 1-2% of attempts, often necessitating repeat procedures.[3] Overall maternal morbidity is minimal, with severe complications like sepsis or hemorrhage reported in under 0.1% of cases in contemporary practice.[24]Fetal and Pregnancy Outcomes
Chorionic villus sampling (CVS) carries a procedure-related risk of fetal loss estimated at 0.2% to 0.5% in singleton pregnancies, based on meta-analyses adjusting for background miscarriage rates. A systematic review of over 63,000 procedures reported a weighted pregnancy loss rate of 0.82% (95% CI, 0.51-1.13%) following CVS, with the attributable risk after background adjustment being approximately 0.27% for transcervical approaches using forceps. Transabdominal CVS, the preferred method in contemporary practice, shows no significant difference in pregnancy loss compared to midtrimester amniocentesis. In twin pregnancies, fetal loss rates post-CVS are around 2.0% (95% CI, 0.0-6.5%), comparable to background rates of 1.8-2.4%. Recent single-center data from 2024-2025 report fetal loss rates as low as 0.15-0.28%, reflecting improvements in technique and gestational timing.[2][31][32] Fetal structural anomalies linked to CVS are rare and primarily associated with procedures performed before 10 weeks' gestation, including transverse limb reduction defects due to potential vascular disruption or ischemia. Current guidelines recommend CVS after 10-13 weeks to eliminate this risk, with evidence from cohort studies showing no increased incidence of limb defects or other congenital malformations when delayed. Earlier concerns from 1990s trials, which reported a 1-2% excess risk of anomalies, have not been substantiated in modern series, where absolute risks remain below procedure-related miscarriage rates. No causal link has been established to other outcomes like fetal infection or growth restriction in peer-reviewed analyses.[33][34][4] Pregnancy complications post-CVS include transient vaginal spotting (up to 2-10%), amniotic fluid leakage, and infection, which can indirectly contribute to adverse outcomes if unmanaged. Spontaneous abortion rates in the immediate post-procedure period align with fetal loss estimates above, with no evidence of elevated preterm birth or placental abruption in controlled studies. A 2024 comparative analysis found no differences in perinatal outcomes, including neonatal intensive care admissions or neurodevelopmental delays, between CVS-exposed pregnancies and unexposed controls or amniocentesis cohorts. Long-term follow-up data indicate that surviving fetuses experience outcomes equivalent to the general population, barring underlying genetic conditions detected by the procedure.[3][35][36]Benefits and Efficacy
Advantages Relative to Alternatives
Chorionic villus sampling (CVS) offers earlier gestational timing compared to amniocentesis, typically performed between 10 and 13 weeks of pregnancy versus 15 to 20 weeks for the latter, enabling couples to receive definitive genetic results sooner and potentially allowing for earlier informed decisions regarding pregnancy management.[37][8] This temporal advantage facilitates rapid karyotyping, biochemical assays, and DNA analysis, which can be completed more expeditiously than with amniocentesis-derived samples.[38] Both procedures achieve comparable diagnostic accuracy, exceeding 99% for detecting chromosomal abnormalities such as trisomies, but CVS's earlier application reduces the period of diagnostic uncertainty.[8] Relative to non-invasive prenatal testing (NIPT), CVS provides a confirmatory diagnostic assessment rather than a probabilistic screening, resolving false-positive or indeterminate NIPT results that occur in up to 1-5% of cases for common aneuploidies.[39][40] While NIPT screens cell-free fetal DNA from maternal blood for select chromosomal conditions with high sensitivity (over 99% for trisomy 21), it misses many microdeletions, mosaicism variants, and single-gene disorders detectable via CVS's direct placental tissue analysis.[41][39] Thus, CVS serves as the gold standard for validation when NIPT indicates elevated risk, offering comprehensive cytogenetic and molecular insights unavailable through noninvasive methods.[42]Accuracy and Reliability Data
Cytogenetic analysis of chorionic villus samples via karyotyping detects non-mosaic whole chromosome abnormalities, such as trisomy 21, with nearly 100% accuracy when the procedure succeeds.[16] A retrospective analysis of 62,865 CVS samples from 1986-1992 reported overall sensitivity of 98.9-99.6% and specificity of 98.5-98.8% for chromosomal aberrations, with negative predictive values exceeding 99.95%.[43] Positive predictive values ranged from 72.6-78.3%, reflecting challenges from confined placental mosaicism (CPM), where placental cells exhibit abnormalities absent in the fetus.[43] CPM occurs in 1-2% of CVS procedures, potentially leading to false-positive results; in these instances, only about 10% involve true fetal mosaicism, necessitating confirmatory amniocentesis for resolution.[1] False-negative rates are rare at 0.03%, primarily in high-risk pregnancies.[43] Procedure success, measured by successful cell culturing, reaches 96.3% in contemporary series, with failures due to insufficient material (2.5%) or maternal cell contamination (1%).[22] For trisomy 21 confirmation following high-risk noninvasive prenatal testing, CVS achieves definitive diagnoses in 97.5% of cases, underscoring its reliability as a diagnostic follow-up despite mosaicism risks.[44] Reliability is enhanced by ultrasound guidance and experienced operators, though direct preparations alone may underperform in high-risk scenarios without long-term culturing.[43]| Metric | Range/Value | Source |
|---|---|---|
| Sensitivity | 98.9-99.6% | EUCROMIC study (n=62,865)[43] |
| Specificity | 98.5-98.8% | EUCROMIC study (n=62,865)[43] |
| Positive Predictive Value | 72.6-78.3% | EUCROMIC study (n=62,865)[43] |
| Negative Predictive Value | 99.95-99.98% | EUCROMIC study (n=62,865)[43] |
| Confined Placental Mosaicism Rate | 1-2% | Systematic reviews[1] |
| Culture Success Rate | 96.3% | 5-year tertiary center study (n=468)[22] |