Performance of conventional cytogenetic analysis on chorionic villi when only one cell layer, cytotrophoblast or mesenchyme alone, is analyzed.

OBJECTIVE: To provide an estimation of the probability of error when chorionic villi (CV) cytogenetic analysis is limited to a single placental layer; either a direct preparation (Dir) or long-term culture (LTC). METHODS: We retrospectively reviewed cytogenetic studies on 81,593 consecutive CV samples in which both Dir and LTC were analyzed. All mosaic cases received amniocentesis. The false omission and false discovery rates were calculated by assessing the results that would have been reported when analysis was limited to either Dir or LTC. RESULTS: For all abnormalities combined, the proportion of normal Dir or LTC only reports that would have been inconsistent with a subsequent amniocentesis was 0.09% and 0.03%, respectively (false omissions). Among abnormal reports based on Dir or LTC alone, 8.01% and 3.17%, respectively, would be inconsistent with a subsequent amniocentesis result (false discoveries). Differences are present for individual abnormalities. CONCLUSIONS: From the perspective of identifying all abnormalities of potential clinical significance, the analysis of both placental layers is optimal. LTC alone is the preferred approach if only one layer of placenta is to be analyzed. Although rare, it is important to acknowledge that one cell layer analysis alone can cause misdiagnosis due to undetected mosaicism.

Outcomes in pregnancies with a confined placental mosaicism and implications for prenatal screening using cell-free DNA.

PURPOSE: To assess the association between confined placental mosaicism (CPM) and adverse pregnancy outcome. METHODS: A retrospective cohort study was carried out evaluating the outcome of pregnancies with and without CPM involving a rare autosomal trisomy (RAT) or tetraploidy. Birthweight, gestational age at delivery, fetal growth restriction (FGR), Apgar score, neonatal intensive care admission, preterm delivery, and hypertensive disorders of pregnancy were considered. RESULTS: Overall 181 pregnancies with CPM and 757 controls were recruited. Outcome information was available for 69% of cases (n = 124) and 62% of controls (n = 468). CPM involving trisomy 16 (T16) was associated with increased incidence of birthweight <3rd centile (P = 0.007, odds ratio [OR] = 11.2, 95% confidence interval [CI] = 2.7-47.1) and preterm delivery (P = 0.029, OR = 10.2, 95% CI = 1.9-54.7). For the other RATs, an association with prenatally diagnosed FGR was not supported by birthweight data and there were no other strong associations with adverse outcomes. CONCLUSION: Excluding T16, the incidence of adverse pregnancy outcomes for pregnancies carrying a CPM is low. RATs can also be identified through genome-wide cell-free DNA screening. Because most of these will be attributable to CPMs, we conclude that this screening is of minimal benefit.

Risk of Fetal Loss in Pregnancies Undergoing Midtrimester Amniocentesis after Inconclusive Chorionic Villus Sampling.

OBJECTIVE: To estimate the procedure-related risk of miscarriage in pregnancies undergoing amniocentesis (AC) following inconclusive results for a chorionic villus sampling (CVS). METHODS: This was a multicentric retrospective cohort study of patients in which both CVS at 11-13 weeks' gestation and AC at 16-22 weeks were performed between January 1st, 2008, and July 31st, 2017. The primary outcome measure was pregnancy loss prior to 24 weeks gestation; the secondary one was intrauterine demise after 24 weeks. RESULTS: A total of 287 patients underwent transabdominal CVS and AC. Nine patients were lost at follow-up; therefore, the analysis was conducted on a population of 278 patients (275 singletons and 3 dichorionic twin pregnancies). AC was performed because of placental mosaicism (93.6%), failure of direct/semidirect preparation of trophoblastic cells (3.2%), or targeted genetic testing after the diagnosis of an anomaly in the second trimester (3.2%). In continuing pregnancies, there were no fetal losses prior to 24 weeks' gestation. Two intrauterine demises (including 1 fetus with multiple anomalies and growth restriction) in the third trimester were recorded. CONCLUSION: Patients undergoing midtrimester AC because of an inconclusive result of CVS can be reasonably reassured that in general the risk of miscarriage and fetal loss following the procedure is very small.

An evidence-based scoring system for prioritizing mosaic aneuploid embryos following preimplantation genetic screening.

The aim of this study was to devise an evidence-based scoring system for prioritizing mosaic aneuploid embryos for transfer. A retrospective analysis was performed of all sequential cytogenetic and molecular results on chorionic villi samples (n = 72,472) and products of conception (n = 3806) analysed at a single centre. The likelihood that a mosaic aneuploidy detected in chorionic villi samples will involve the fetus, the incidence of clinically significant fetal uniparental disomy in the presence of a mosaic in chorionic villi and the chance of the mosaicism culminating in miscarriage were used to generate a scoring system for prioritizing mosaic aneuploid embryos detected by preimplantation genetic screening. A composite score was obtained for each individual mosaic aneuploidy after assignment of an individual risk score based on the incidence/likelihood of each adverse outcome. A final additional score was assigned to viable full or mosaic aneuploidies with a well-defined phenotype. The higher the composite score the lower the priority for embryo transfer. In conclusion, due to the paucity of prospective studies on the actual transfer of mosaic aneuploid embryos, we suggest using this evidence-based scoring system to provide a useful tool for clinicians, embryologists and patients.

Implications of fetoplacental mosaicism on cell-free DNA testing for sex chromosome aneuploidies.

OBJECTIVE: The unique biological behavior of sex chromosomes has implications for cell-free DNA (cfDNA) testing. Our purpose is to predict the (1) false positive/negative rates of cfDNA testing consequent to fetoplacental mosaicism for any sex chromosome aneuploidies (SCA) and (2) positive predictive value (PPV) and negative predictive values of a high-risk and low-risk cfDNA result for any SCA. METHOD: This is a retrospective analysis of 67 030 chorionic villus sampling karyotypes, including fetoplacental mosaicism cases. RESULTS: Non-mosaic 45, X is associated with cystic hygroma/increased nuchal translucency and fetal anomalies. The false positive rate consequent to confined placental mosaicism is predicted to be 0.05%. The estimated false negative rate is in the range of 0% to 5.7% for all non-mosaic SCAs; it is 70% for mosaic 45, X with normal ultrasound. The predicted PPV on amniocytes is very high for most SCAs (94.4-99.4%). However, the stratified analysis shows that the PPV is much lower for 45, X without ultrasound anomalies compared with 45, X with abnormal scan (51% or 71%, vs 99%, respectively). CONCLUSION: Mosaicism is a major issue for SCA cfDNA testing, and prenatal confirmation, preferentially with amniocentesis if there are no ultrasound anomalies, remains important in counseling. As PPV varies on the basis of the presence of an ultrasound anomaly, skilled evaluation is critical. © 2017 John Wiley & Sons, Ltd.

Internalization of nanopolymeric tracers does not alter characteristics of placental cells.

In the cell therapy scenario, efficient tracing of transplanted cells is essential for investigating cell migration and interactions with host tissues. This is fundamental to provide mechanistic insights which altogether allow for the understanding of the translational potential of placental cell therapy in the clinical setting. Mesenchymal stem/stromal cells (MSC) from human placenta are increasingly being investigated for their potential in treating patients with a variety of diseases. In this study, we investigated the feasibility of using poly (methyl methacrylate) nanoparticles (PMMA-NPs) to trace placental MSC, namely those from the amniotic membrane (hAMSC) and early chorionic villi (hCV-MSC). We report that PMMP-NPs are efficiently internalized and retained in both populations, and do not alter cell morphofunctional parameters. We observed that PMMP-NP incorporation does not alter in vitro immune modulatory capability of placental MSC, a characteristic central to their reparative/therapeutic effects in vitro. We also show that in vitro, PMMP-NP uptake is not affected by hypoxia. Interestingly, after in vivo brain ischaemia and reperfusion injury achieved by transient middle cerebral artery occlusion (tMCAo) in mice, iv hAMSC treatment resulted in significant improvement in cognitive function compared to PBS-treated tMCAo mice. Our study provides evidence that tracing placental MSC with PMMP-NPs does not alter their in vitro and in vivo functions. These observations are grounds for the use of PMMP-NPs as tools to investigate the therapeutic mechanisms of hAMSC and hCV-MSC in preclinical models of inflammatory-driven diseases.

Frequency of fetal karyotype abnormalities in women undergoing invasive testing in the absence of ultrasound and other high-risk indications.

OBJECTIVES: No previous studies have reported the frequencies of individual chromosomal anomalies in normal-appearing fetuses stratified by maternal age (MA) and gestational age (GA). We therefore sought to (1) characterize the frequency of all fetal karyotype anomalies in sonographically normal appearing fetuses without pretest risk factors, and (2) assess MA and GA impact on the proportion of anomalies targeted by screening and consequent impact on residual risk following a negative result. METHODS: Fetal karyotypes from samples without prior risk assessment or ultrasound anomalies were analyzed. We calculated, per single-year MA and in two GA intervals, the predicted frequency of each cytogenetic defect. RESULTS: A total of 129 263 karyotypes were analyzed. The risk for significant, cytogenetically visible chromosomal anomalies, at 15 to 20 weeks GA, varies between 1/301 at MA of 18 years, and 1/9 at MA of 48 years. The proportion of clinically significant anomalies not addressed by current screening methods is 47% at MA of 18 years and 5% at MA of 48 years. CONCLUSIONS: By determining frequencies for individual karyotype anomalies stratified by MA and GA, in the setting of normal-appearing fetuses, a more personalized risk assessment, including the residual risk after a normal fetal aneuploidy screening result, can be provided. © 2016 John Wiley & Sons, Ltd.

Interpreting mosaicism in chorionic villi: results of a monocentric series of 1001 mosaics in chorionic villi with follow-up amniocentesis.

OBJECTIVES: Chromosomal mosaicism in chorionic villi (CV) is detected in ~1-2% of cases. When a mosaic in CV is detected during prenatal diagnosis, a confirmatory karyotype should be performed on amniocytes to discriminate between a mosaic confined to the placenta [confined placental mosaicism (CPM)] and one generalized to the fetus [true fetal mosaicism (TFM)]. We determined the likelihood that any mosaic abnormalities identified through CV samples are confirmed in the fetus. METHODS: Over a period of 14 years, the laboratory analyzed both the cytotrophoblast and the mesenchyme of 60 347 CV samples. Cytogenetic results from CV samples showing mosaicism with follow-up amniocentesis were considered. The incidence of CPM and TFM and the risk of confirmation in the amniotic fluid (AF) were calculated. Uniparental disomy (UPD) was tested on ~300 cases at risk due to involvement of an imprinted chromosome. RESULTS: Overall, 1317 mosaic CV cases (2.18%) were detected, of which 1001 were subsequently investigated by amniocentesis. The overall risk of TFM was 13% and UPD incidence was 2.1%. CONCLUSIONS: The very large presented sample set and consistency in cytogenetic methodology, especially the analysis of both placental layers performed on all CV samples will enable genetic counselors to determine the risk of fetal involvement and the clinical relevance of an identified mosaic condition.

The type of feto-placental aneuploidy detected by cfDNA testing may influence the choice of confirmatory diagnostic procedure.

OBJECTIVES: Cell-free DNA (cfDNA) screening can provide false positive/negative results because the fetal fraction originates primarily from trophoblast. Consequently, invasive diagnostic testing is recommended to confirm a high-risk result. Currently, there is debate about the most appropriate invasive method. We sought to estimate the frequency in which a chorionic villus sampling (CVS) performed after a high-risk cfDNA result would require a follow-up amniocentesis due to placental mosaicism. METHODS: Analyses of the frequencies of the different types of mosaicism involving cytotrophoblasts, for trisomies 21 (T21), 18 (T18), 13 (T13) and monosomy X (MX) among 52,673 CVS karyotypes obtained from cytotrophoblast, mesenchyme and confirmatory amniocentesis. RESULTS: After a high-risk cfDNA result for T21, 18, 13 and MX, the likelihood of finding CVS mosaicism and need for amniocentesis is, respectively, 2%, 4%, 22% and 59%. When mosaicism is detected by CVS, the likelihood of fetal confirmation by amniocentesis is, respectively, 44%, 14%, 4% and 26%. CONCLUSIONS: In cases of high-risk cfDNA results for T21/T18, CVS (combining cytotrophoblast and mesenchyme analysis) can be considered, but with the caveat of 2-4% risk of an inconclusive result requiring further testing. In high-risk results for MX/T13, amniocentesis would appear to be the most appropriate follow-up diagnostic test, especially in the absence of sonographic findings.

Prenatal diagnosis of 24 cases of microduplication 22q11.2: an investigation of phenotype-genotype correlations.

OBJECTIVE: Microduplication 22q11.2 is primarily characterized by a highly variable clinical phenotype, which ranges from apparently normal or slightly dysmorphic features (in the presence or absence of learning disorders) to severe malformations with profound mental retardation. Hence, genetic counseling is particularly challenging when microduplication 22q11.2 is identified in a prenatal diagnosis. Here, we report on 24 prenatal cases of microduplication 22q11.2. METHODS: Seventeen of the cases were also reanalyzed by microarray analysis, in order to determine copy number variations (CNVs, which are thought to influence expressivity). We also searched for possible correlations between fetal phenotypes, indications for invasive prenatal diagnosis, inheritance, and pregnancy outcomes. RESULTS: Of the 24 cases, 15 were inherited, six occurred de novo, and three were of unknown origin. Termination of pregnancy occurred in seven cases and was mainly decided on the basis of ultrasound findings. Moreover, additional CNVs were found in some patients and we try to make a genotype-phenotype correlation. CONCLUSION: We discuss the complexity of genetic counseling for microduplication 22q11.2 and comment on possible explanations for the clinical heterogeneity of this syndrome. In particular, we assessed the co-existence of additional CNVs and their contribution to phenotypic variations in chromosome 22q11.2 microduplication syndrome.

Prevalence of recurrent pathogenic microdeletions and microduplications in over 9500 pregnancies.

OBJECTIVES: The implementation of chromosomal microarray analysis (CMA) in prenatal testing for all patients has not achieved a consensus. Technical alternatives such as Prenatal BACs-on-Beads(TM) (PNBoBs(TM) ) have thus been applied. The aim of this study was to provide the frequencies of the submicroscopic defects detectable by PNBoBs(TM) under different prenatal indications. METHODS: A total of 9648 prenatal samples were prospectively analyzed by karyotyping plus PNBoBs(TM) and classified by prenatal indication. The frequencies of the genomic defects and their 95%CIs were calculated for each indication. RESULTS: The overall incidence of cryptic imbalances was 0.7%. The majority involved the DiGeorge syndrome critical region (DGS). The additional diagnostic yield of PNBoBs(TM) in the population with a low a priori risk was 1/298. The prevalences of DGS microdeletion and microduplication in the low-risk population were 1/992 and 1/850, respectively. CONCLUSIONS: The constant a priori risk for common pathogenic cryptic imbalances detected by this technology is estimated to be ~0.3%. A prevalence higher than that previously estimated was found for the 22q11.2 microdeletion. Their frequencies were independent of maternal age. These data have implications for cell-free DNA screening tests design and justify prenatal screening for 22q11 deletion, as early recognition of DGS improves its prognosis.

Fetoplacental mosaicism: potential implications for false-positive and false-negative noninvasive prenatal screening results.

PURPOSE: Noninvasive prenatal screening for fetal aneuploidy analyzes cell-free fetal DNA circulating in the maternal plasma. Because cell-free fetal DNA is mainly of placental trophoblast origin, false-positive and false-negative findings may result from placental mosaicism. The aim of this study was to calculate the potential contribution of placental mosaicism in discordant results of noninvasive prenatal screening. METHODS: We performed a retrospective audit of 52,673 chorionic villus samples in which cytogenetic analysis of the cytotrophoblast (direct) and villus mesenchyme (culture) was performed, which was followed by confirmatory amniocentesis in chorionic villi mosaic cases. Using cases in which cytogenetic discordance between cytotrophoblast and amniotic fluid samples was identified, we calculated the potential contribution of cell line-specific mosaicism to false-positive and false-negative results of noninvasive prenatal screening. RESULTS: The false-positive rate, secondary to the presence of abnormal cell line with common trisomies in cytotrophoblast and normal amniotic fluid, ranged from 1/1,065 to 1/3,931 at 10% and 100% mosaicism, respectively; the false-negative rate was calculated from cases of true fetal mosaicism, in which a mosaic cell line was absent in cytotrophoblast and present in the fetus; this occurred in 1/107 cases. CONCLUSION: Despite exciting advances, underlying biologic mechanisms will never allow 100% sensitivity or specificity.

De novo small supernumerary marker chromosomes detected on 143,000 consecutive prenatal diagnoses: chromosomal distribution, frequencies, and characterization combining molecular cytogenetics approaches.

OBJECTIVE: The risk of clinical consequences in prenatal cases with de novo small supernumerary marker chromosomes (sSMC), often in mosaic conditions, is not easy to predict, which results in difficulties in genetic counseling. METHOD: In this study, we evaluated the frequency, the chromosomal origin, and the clinical indication of 104 de novo sSMC detected in a monocenter survey on the basis of 143,000 consecutive prenatal diagnoses, and we assessed the reliability of molecular cytogenetics technologies for sSMC characterization. RESULTS: We detected a de novo sSMC frequency of 0.072%. Its incidence in advanced maternal age group is statistically different from that found in maternal anxiety indication (<35 years old). A higher prevalence of mosaicism in chorionic villi sampling (CVS) than in amniotic fluids was also revealed related to confined placental mosaicisms. The risk of confirmation in amniotic fluids of mosaics previously revealed at CVS was 33.3%. No uniparental disomy conditions were found when imprinted chromosomes were involved in the occurrence of de novo sSMC. The majority of de novo sSMC were acrocentric derived-chromosomes, and a neocentromere formation was observed in one pregnancy. CONCLUSION: Our data support that array comparative genomic hybridization has improved sSMC characterization and demonstrate its utility in supporting genetic counseling. We propose a workflow for de novo sSMC characterization.

Fetal mesenchymal stromal cells from cryopreserved human chorionic villi: cytogenetic and molecular analysis of genome stability in long-term cultures.

BACKGROUND AIMS: First-trimester chorionic villi (CV) are an attractive source of human mesenchymal stromal cells (hMSC) for possible applications in cellular therapy and regenerative medicine. Human MSC from CV were monitored for genetic stability in long-term cultures. METHODS: We set up a good manufacturing practice cryopreservation procedure for small amounts of native CV samples. After isolation, hMSC were in vitro cultured and analyzed for biological end points. Genome stability at different passages of expansion was explored by karyotype, genome-wide array-comparative genomic hybridization and microsatellite genotyping. RESULTS: Growth curve analysis revealed a high proliferative potential of CV-derived cells. Immunophenotyping showed expression of typical MSC markers and absence of hematopoietic markers. Analysis of multilineage potential demonstrated efficient differentiation into adipocytes, osteocytes, chondrocytes and induction of neuro-glial commitment. In angiogenic experiments, differentiation in endothelial cells was detected by in vitro Matrigel assay after vascular endothelial growth factor stimulation. Data obtained from karyotyping, array-comparative genomic hybridization and microsatellite genotyping comparing early with late DNA passages did not show any genomic variation at least up to passage 10. Aneuploid clones appeared in four of 14 cases at latest passages, immediately before culture growth arrest. CONCLUSIONS: Our findings indicate that hCV-MSC are genetically stable in long-term cultures at least up to passage 10 and that it is possible to achieve clinically relevant amounts of hCV-MSC even after few stages of expansion. Genome abnormalities at higher passages can occasionally occur and are always associated with spontaneous growth arrest. Under these circumstances, hCV-MSC could be suitable for therapeutic purposes.

QF-PCR as a substitute for karyotyping of cytotrophoblast for the analysis of chorionic villi: advantages and limitations from a cytogenetic retrospective audit of 44,727 first-trimester prenatal diagnoses.

OBJECTIVES: Karyotyping on chorionic villous samples (CVS) includes the analysis of both cytotrophoblast (STC) and mesenchyme (LTC). This approach requires complex laboratory organization and trained technicians. The introduction of quantitative fluorescent polymerase chain reaction (QF-PCR) instead of conventional karyotyping in low-risk pregnancies opened its application in CVS analysis. Discordant QF-PCR and CVS cytogenetic results were reported, and strategies for CVS analysis were introduced to minimize this risk. The possibility to substitute the STC with QF-PCR was reported. The aim of this study is to evaluate benefits and limitations of the approach QF-PCR + LTC compared with the traditional method STC + LTC and to quantify the associated risks of false results. METHOD: This study is based on a retrospective cytogenetic audit of CVS results (n = 44 727) generated by the STC + LTC analytic approach. False-negative risks related to true fetal mosaicism type IV, imprinting syndromes and maternal contamination in LTC were calculated. RESULTS: Compared with STC + LTC, QF-PCR + LTC approach is associated with a cumulative false-negative risk of ~1/3100-1/4400. Costs and reporting time of STC in a high-throughput cytogenetic lab are similar to a CE-IVD marked QF-PCR analysis. CONCLUSIONS: These results should be clearly highlighted in the pre-test counseling and extensively discussed with the couple prior to testing for informed consent.

Application of a new molecular technique for the genetic evaluation of products of conception.

OBJECTIVES: Karyotyping is a well-established method of investigating the genetic content of product of conceptions (POCs). Because of the high rate of culture failure and maternal cell contamination, failed results or 46,XX findings are often obtained. Different molecular approaches that are not culture dependent have been proposed to circumvent these limits. On the basis of the robust experience previously obtained with bacterial artificial chromosomes (BACs)-on-Beads™ (BoBs™), we evaluated the same technology that we had used for the analysis of prenatal samples on POCs. METHOD: KaryoLite™ BoBs™ includes 91 beads, each of which is conjugated with a composite of multiple neighboring BACs according to the hg19 assembly. It quantifies proximal and terminal regions of each chromosome arm. The study included 376 samples. RESULTS: The failure rate was 2%, and reproducibility >99%; false-positive and false-negative rates were <1% for non-mosaic aneuploidies and imbalances effecting all three BACs in a contig. Detection rate for partial terminal imbalances was 65.5%. The mosaic detection threshold was 50%, and the success rate in macerated samples was 87.8%. The aneuploidy detection rate in samples with cell growth failure was 27.8%, and maternal cell contamination was suspected in 23.1% of 46,XX cultured cells. CONCLUSION: KaryoLite™ BoBs™ as a 'first-tier' test in combination with other approaches showed beneficial, cost-effective and clearly enhanced POC testing.

Prenatal BACs-on-Beads™: the prospective experience of five prenatal diagnosis laboratories.

OBJECTIVE: We previously reported on the validation of Prenatal BACs-on-Beads™ on retrospectively selected and prospective prenatal samples. This bead-based multiplex assay detects chromosome 13, 18, 21 and X/Y aneuploidies and the nine most frequent microdeletion syndromes. We demonstrated that Prenatal BACs-on-Beads(TM) is a new-generation, prenatal screening tool. Here, we describe the experience of five European prenatal diagnosis laboratories concerning the ongoing use of Prenatal BACs-on-Beads™ . METHODS: Some 1653 samples were analyzed. All results were confirmed by conventional karyotyping or another appropriate technique. All indications for invasive prenatal diagnosis were included. Amniotic fluid and chorionic villus samples were analyzed in equivalent proportions. RESULTS: The failure rate was 3.3% and the overall abnormality detection rate was ~1/10. Eighty-five percent of the detected abnormalities were common aneuploidies. Eleven microdeletions and duplications were identified, thus giving an overall yield for microdeletion and microduplication detection of 1/145. Compared with QF-PCR, Prenatal BACs-on-Beads™ provides an additional detection rate of ~1/250 for low-risk pregnancies. The false positive and negative rates were both <1%. CONCLUSION: When associated with conventional karyotyping, the Prenatal BACs-on-Beads™ assay combines a short turnaround time (typical of rapid aneuploidy detection tests) with valuable detection of the most frequent microdeletion syndromes that cannot be detected in cytogenetic analyses.

Chromosome abnormalities investigated by non-invasive prenatal testing account for approximately 50% of fetal unbalances associated with relevant clinical phenotypes.

During the past 20 years non-invasive screening tests have been increasingly utilized in prenatal diagnosis (PD) practice. Considerable effort has been exerted by multicenter consortia to evaluate the reliability of non-invasive screening tests in detecting those women with an increased risk of having a pregnancy affected by trisomies 21, 18, and 13, monosomy X, and triploidies. To what extent this group of abnormal karyotypes accounts for the total number of phenotypically relevant fetal chromosome abnormalities has, however, never been investigated. The present report is an attempt aimed to quantify this proportion. A retrospective analysis of a homogeneous survey of 115,128 consecutive invasive prenatal tests was undertaken. All cases were classified in accordance with the indication given for the invasive testing. Cytogenetic results regarding 96,416 karyotype analyses performed because of advanced maternal age (>or=35 years) or gestational anxiety (<35 years) were considered since these are the patients who usually undergo non-invasive screening tests. We calculated the number of cases (T21, T18, T13, 45,X, and triploidy) that would have been detected by prenatal screening on the basis of the published detection rate of the combined-2 test or the quadruple test. Our findings indicate that the chromosomal abnormalities investigated by screening tests represent <50% of the fetal chromosomal abnormalities associated with an abnormal outcome ranging from intermediate-to-severe in women <35 years (45.8% and 39.6% in the first and second trimesters, respectively), and sensitivity >50% in women >or=35 years (65.1% and 61.8%, respectively). To conclude, approximately 50% of the phenotypically relevant abnormal karyotypes cannot be detected by non-invasive prenatal screening tests.