International, collaborative assessment of 146,000 prenatal karyotypes: expected limitations if only chromosome-specific probes and fluorescent in-situ hybridization are used

Prenatal Invasive Testing at a Tertiary Referral Center in India: A Report of 433 Cases Under a Single Operator

PURPOSE OF THE STUDY

Chromosomal aneuploidies are major causes of perinatal death and childhood handicap. Awareness about screening and prenatal diagnosis for these disorders among obstetricians and primary care physicians is increasing. Since invasive tests like amniocentesis or chorionic villus sampling (CVS) are associated with a risk of miscarriage these tests should be carried out judiciously in pregnancies considered to be at high risk for aneuploidies and other genetic disorders. The purpose of our study was to examine the patterns, trends and outcomes of the various screening procedures and invasive tests results.

METHODOLOGY

Retrospective observational study done over a period of 3 years and one month including 433 pregnant women with high risk for genetic disorders undergoing invasive prenatal testing like chorionic villus sampling, amniocentesis or cordocentesis. Data were collected from our department records regarding the maternal age, indication for invasive testing, past obstetric history, family history of genetic syndromes, ultrasound findings in the current sonographic examination and the results of the tests done. Any immediate or late complications of the procedure if any were telephonically addressed.

RESULTS

A total of 436 procedures on 433 patients (418 singleton,12 single fetus of twin, 3 both fetuses of twins) were done out of which 281 were amniocentesis(64.4%), 153 were chorionic villus sampling (35.1%) and 2 were cordocentesis(< 1%). Of the 436 procedures, 373(85.5%) were done for positive screening tests for chromosomal aneuploidies and 63(14.4%) were done for previous history of genetic syndromes. The positive predictive value of biochemical marker alone was around 2.7% and higher around 13% for a combined first trimester or a second-trimester screen along with ultrasound abnormalities. The higher the biochemical risk does not translate into higher chance of chromosomal abnormality. Nineteen percentage of fetuses with NT above 95th centile had chromosomal abnormality. Twenty-one percentage of fetuses with absent nasal bone in our study had trisomy 21.

CONCLUSION

Aneuploidy screening is the most common indication for prenatal invasive testing with dual marker combined with nuchal translucency, nasal bone, tricuspid regurgitation and ductus venosus flow providing the best detection rates. The chance of an affected fetus in a patient with aneuploidy screen positive overall is only 6.7%.

Women should decide which conditions matter

Providing reliable prenatal screening performance estimates is critical for patient counseling and policy-making. Women who choose prenatal screening for aneuploidy are likely to be concerned not only with the common aneuploidies but with all causes of intellectual disability and serious birth defects. Sequential prenatal screening (combined serum and ultrasound testing) for aneuploidy detection commonly is offered as a primary screening test. Among women identified as screen positive, cell-free (cf)DNA has been added recently as a secondary, noninvasive screening option, before the consideration of invasive diagnostic testing (eg, amniocentesis and karyotype). With the anticipation of lower costs in the future, cfDNA might be an alternative to sequential screening in the general population. Sequential and cfDNA tests are both noninvasive, and both identify common aneuploidies. Screening via cfDNA detects more common chromosome abnormalities (eg, trisomy 21, sex trisomies). Sequential screening can identify other aneuploidies (eg, triploidy), as well as chromosome abnormalities associated with fetal structural abnormalities. When the advantages and disadvantages of routine sequential screening with routine cfDNA screening are compared, one important measure is the proportion and severity of chromosome abnormalities identified. When reporting these detection rates, authors need to carefully consider the impact of multiple well-described biases. For women to make informed choices in situations of this type, determining reliable comparative performance estimates is crucial.

Noninvasive prenatal screening or advanced diagnostic testing: caveat emptor

The past few years have seen extraordinary advances in prenatal genetic practice led by 2 major technological advances; next-generation sequencing of cell-free DNA in the maternal plasma to noninvasively identify fetal chromosome abnormalities, and microarray analysis of chorionic villus sampling and amniotic fluid samples, resulting in increased cytogenetic resolution. Noninvasive prenatal screening of cell-free DNA has demonstrated sensitivity and specificity for trisomy 21 superior to all previous screening approaches with slightly lower performance for other common aneuploidies. These tests have rapidly captured an increasing market share, with substantial reductions in the number of chorionic villus sampling and amniocentesis performed suggesting that physicians and patients regard such screening approaches as an equivalent replacement for diagnostic testing. Simultaneously, many clinical programs have noted significant decreases in patient counseling. In 2012 the Eunice Kennedy Shriver National Institute of Child Health and Human Development funded a blinded comparison of karyotype with the emerging technology of array comparative genomic hybridization showing that in patients with a normal karyotype, 2.5% had a clinically relevant microdeletion or duplication identified. In pregnancies with an ultrasound-detected structural anomaly, 6% had an incremental finding, and of those with a normal scan, 1.6% had a copy number variant. For patients of any age with a normal ultrasound and karyotype, the chance of a pathogenic copy number variant is greater than 1%, similar to the age-related risk of aneuploidy in the fetus of a 38 year old. This risk is 4-fold higher than the risk of trisomy 21 in a woman younger than 30 years and 5- to 10-fold higher than the present accepted risk of a diagnostic procedure. Based on this, we contend that every patient, regardless of her age, be educated about these risks and offered the opportunity to have a diagnostic procedure with array comparative genomic hybridization performed.

Chromosomal Microarrays for the Prenatal Detection of Microdeletions and Microduplications

Chromosomal microarray analysis has replaced conventional G-banded karyotype in prenatal diagnosis as the first-tier test for the cytogenetic detection of copy number imbalances in fetuses with/without major structural abnormalities. This article reviews the basic technology of microarray; the value and clinical significance of the detection of microdeletions, microduplications, and other copy number variants; as well as the importance of genetic counseling for prenatal diagnosis. It also discusses the current status of noninvasive screening for some of these microdeletion and microduplication syndromes.

Non-invasive prenatal testing (NIPT): limitations on the way to become diagnosis

With the discovery of existing circulating cell-free fetal DNA (ccffDNA) in maternal plasma and the advent of next-generation sequencing (NGS) technology, there is substantial hope that prenatal diagnosis will become a predominately non-invasive process in the future. At the moment, non-invasive prenatal testing (NIPT) is available for high-risk pregnancies with significant better sensitivity and specificity than the other existing non-invasive methods (biochemical and ultrasonographical). Mainly it is performed by NGS methods in a few commercial labs worldwide. However, it is expected that many other labs will offer analogous services in the future in this fast-growing field with a multiplicity of in-house methods (e.g., epigenetic, etc.). Due to various limitations of the available methods and technologies that are explained in detail in this manuscript, NIPT has not become diagnostic yet and women may still need to undergo risky invasive procedures to verify a positive finding or to secure (or even expand) a negative one. Efforts have already started to make the NIPT technologies more accurate (even at the level of a complete fetal genome) and cheaper and thus more affordable, in order to become diagnostic screening tests for all pregnancies in the near future.

Detection of sex chromosome aneuploidies using quantitative fluorescent PCR in the Hungarian population

BACKGROUND

Aneuploidies are the most frequent chromosomal abnormalities at birth. Autosomal aneuploidies cause serious malformations like trisomy 21, trisomy 18 and trisomy 13. However sex chromosome aneuploidies are causing less severe syndromes. For the detection of these aneuploidies, the "gold standard" method is the cytogenetic analysis of fetal cells, karyograms show all numerical and structural abnormalities, but it takes 2-4 weeks to get the reports. Molecular biological methods were developed to overcome the long culture time, thus, FISH and quantitative fluorescent PCR were introduced. In this work we show our experience with a commercial kit for the detection of sex chromosome aneuploidies.

METHODS

We analyzed 20.173 amniotic fluid samples for the period of 2006-2013 in our department. A conventional cytogenetic analysis was performed on the samples. We checked the reliability of quantitative fluorescent PCR and DNA fragment analysis on those samples where sex chromosomal aneuploidy was diagnosed.

RESULTS

From the 20.173 amniotic fluid samples we found 50 samples with sex chromosome aneuploidy. There were 19 samples showing 46, XO, 17 samples with 46, XXY, 9 samples with 47, XXX and 5 samples with 47, XYY karyotypes. The applied quantitative fluorescent PCR and DNA fragment analyses method are suitable to detect all abnormal sex chromosome aneuploidies.

CONCLUSIONS

Quantitative fluorescent PCR is a fast and reliable method for detection of sex chromosome aneuploidies.

Potential diagnostic consequences of applying non-invasive prenatal testing: population-based study from a country with existing first-trimester screening

OBJECTIVES

Targeted non-invasive prenatal testing (NIPT) tests for trisomies 21, 18 and 13 and sex chromosome aneuploidies and could be an alternative to traditional karyotyping. The aim of this study was to determine the risk of missing other abnormal karyotypes of probable phenotypic significance by NIPT.

METHODS

This was a retrospective population-based analysis of all singleton pregnancies booked for combined first-trimester screening (cFTS) in Denmark over a 4-year period. Data concerning maternal demographics, cFTS and prenatal or postnatal karyotypes were collected from the Danish Fetal Medicine database. Karyotypes were classified according to whether the chromosomal anomaly would have been detected by NIPT and whether it was likely to affect phenotype.

RESULTS

cFTS was completed in 193638 pregnancies. 10205 (5.3%) had cytogenetic or molecular analysis performed. Of these, 1122 (11.0%) had an abnormal karyotype, of which 262 (23.4%) would have been missed by NIPT, but would probably have been clinically significant. The prevalence of such 'atypical abnormal karyotypes' was increased in women above 45 years of age, in pregnancies with increased nuchal translucency (NT) thickness (≥ 3.5 mm), with abnormal levels of free β-human chorionic gonadotropin (<0.2 or ≥ 5.0 multiples of the median (MoM)) or pregnancy-associated plasma protein-A<0.2 MoM. One or more of these factors was present in 3% of women, and the prevalence of atypical abnormal karyotypes in this high-risk cohort was 1.6%.

CONCLUSIONS

A significant proportion of karyotypic abnormalities will be missed by targeted NIPT. Women of advanced maternal age, or with increased fetal NT or abnormal biochemistry, have a higher risk of having a fetus affected by an atypical abnormal karyotype and need to be counseled accordingly when considering NIPT.

Rapid-prenatal diagnosis through fluorescence in situ hybridization for preventing aneuploidy related birth defects

BACKGROUND AND OBJECTIVE:

Women with high-risk pregnancies are offered prenatal diagnosis through amniocentesis for cytogenetic analysis of fetal cells. The aim of this study was to evaluate the effectiveness of the rapid fluorescence in situ hybridization (FISH) technique for detecting numerical aberrations of chromosomes 13, 21, 18, X and Y in high-risk pregnancies in an Indian scenario.

MATERIALS AND METHODS:

A total of 163 samples were received for a FISH and/or a full karyotype for prenatal diagnosis from high-risk pregnancies. In 116 samples both conventional culture techniques for getting karyotype through G-banding techniques were applied in conjunction to FISH test using the AneuVysion kit (Abbott Molecular, Inc.), following standard recommended protocol to compare the both the techniques in our setup.

RESULTS:

Out of 116 patients, we got 96 normal for the five major chromosome abnormality and seven patients were found to be abnormal (04 trisomy 21, 02 monosomy X, and 01 trisomy 13) and all the FISH results correlated with conventional cytogenetics. To summarize the results of total 163 patients for the major chromosomal abnormalities analyzed by both/or cytogenetics and FISH there were 140 (86%) normal, 9 (6%) cases were abnormal and another 4 (2.5%) cases were suspicious mosaic and 10 (6%) cases of culture failure. The diagnostic detection rate with FISH in 116 patients was 97.5%. There were no false-positive and false-negative autosomal or sex chromosomal results, within our established criteria for reporting FISH signals.

CONCLUSION:

Rapid FISH is a reliable and prompt method for detecting numerical chromosomal aberrations and has now been implemented as a routine diagnostic procedure for detection of fetal aneuploidy in India.

Non-invasive prenatal testing for aneuploidy: current status and future prospects

Non-invasive prenatal testing (NIPT) for aneuploidy using cell-free DNA in maternal plasma is revolutionizing prenatal screening and diagnosis. We review NIPT in the context of established screening and invasive technologies, the range of cytogenetic abnormalities detectable, cost, counseling and ethical issues. Current NIPT approaches involve whole-genome sequencing, targeted sequencing and assessment of single nucleotide polymorphism (SNP) differences between mother and fetus. Clinical trials have demonstrated the efficacy of NIPT for Down and Edwards syndromes, and possibly Patau syndrome, in high-risk women. Universal NIPT is not cost-effective, but using NIPT contingently in women found at moderate or high risk by conventional screening is cost-effective. Positive NIPT results must be confirmed using invasive techniques. Established screening, fetal ultrasound and invasive procedures with microarray testing allow the detection of a broad range of additional abnormalities not yet detectable by NIPT. NIPT approaches that take advantage of SNP information potentially allow the identification of parent of origin for imbalances, triploidy, uniparental disomy and consanguinity, and separate evaluation of dizygotic twins. Fetal fraction enrichment, improved sequencing and selected analysis of the most informative sequences should result in tests for additional chromosomal abnormalities. Providing adequate prenatal counseling poses a substantial challenge given the broad range of prenatal testing options now available.

Antenatal diagnosis and management of life-limiting conditions

Whereas structural fetal abnormalities are relatively frequent occurrences, many of these do not impact measurably on future life and/or are amenable to postnatal therapy. A small minority are considered to be potentially lethal or life-limiting. Examples include specific skeletal dysplasias, urinary tract abnormalities - typically those which lead to anhydramnios and pulmonary hypoplasia, some disorders of the central nervous system and trisomies 13 and 18. Without seeking to compile an exhaustive list of such conditions, we discuss the principles and new considerations in relation to antenatal diagnosis and perinatal management of such disorders.

Non-invasive prenatal diagnostics using next generation sequencing: technical, legal and social challenges

INTRODUCTION

Newly developed non-invasive prenatal diagnostic techniques, using maternal blood samples, have the potential to reduce or obviate the need for invasive prenatal diagnostic practices such as amniocentesis or chorionic villous sampling. This will lead to a change in how obstetric care is extended by health care providers to pregnant women at-risk of bearing an aneuploid child.

AREAS COVERED

The process leading to the development of fetal aneuploidy detection via the analysis of cell-free DNA in maternal plasma by massive parallel sequencing. Optimization of these strategies and approaches used in the recent or up-coming commercial launches. In addition, this review provides insight into legal implications, potential patent disputes, ethical and societal concerns raised by this development, such as whole genome data storage, retrieval and access.

EXPERT OPINION

There is a need for engagement by professional societies, to ensure correct usage of these newly emerging technologies and their restriction to high-risk pregnancies. National agencies need to ensure the necessary degree of high quality required for prenatal diagnosis.

Diagnostic utility of array-based comparative genomic hybridization (aCGH) in a prenatal setting

OBJECTIVE

Array-based comparative genomic hybridization (aCGH) is a new technique for detecting submicroscopic deletions and duplications. There is limited information regarding its use in the prenatal setting. Here, we present our experience of 269 prenatal aCGHs between 2006 and 2009.

METHOD

The indications for testing were fetal anomalies on ultrasound (U/S), advanced maternal age (AMA), family history of a disorder of unknown etiology, parental concern, abnormal routine karyotype and abnormal serum biochemical screening for common fetal aneuploidies.

RESULTS

Of 15 cases with a known abnormal karyotype, 11 had a normal aCGH. This enabled us to reassure the families and the pregnancies were continued. The remaining four showed an abnormal aCGH, confirming the chromosomes were unbalanced, and were terminated. Of 254 cases with a normal karyotype, 3 had an abnormal aCGH and were terminated. Overall, new clinically relevant results were detected by aCGH in 18 cases, providing additional information for prenatal genetic counseling and risk assessment.

CONCLUSION

Our results suggest that prenatal aCGH should be offered particularly in cases with abnormal U/S. We found the rate of detecting an abnormality by aCGH in low-risk pregnancies was 1:84, but larger studies will be needed to expand our knowledge and validate our conclusions.

Rapid testing versus karyotyping in Down's syndrome screening: cost-effectiveness and detection of clinically significant chromosome abnormalities

In all, 80% of antenatal karyotypes are generated by Down's syndrome screening programmes (DSSP). After a positive screening, women are offered prenatal foetus karyotyping, the gold standard. Reliable molecular methods for rapid aneuploidy diagnosis (RAD: fluorescence in situ hybridization (FISH) and quantitative fluorescence PCR (QF-PCR)) can detect common aneuploidies, and are faster and less expensive than karyotyping.In the UK, RAD is recommended as a standalone approach in DSSP, whereas the US guidelines recommend that RAD be followed up by karyotyping. A cost-effectiveness (CE) analysis of RAD in various DSSP is lacking. There is a debate over the significance of chromosome abnormalities (CA) detected with karyotyping but not using RAD. Our objectives were to compare the CE of RAD versus karyotyping, to evaluate the clinically significant missed CA and to determine the impact of detecting the missed CA. We performed computer simulations to compare six screening options followed by FISH, PCR or karyotyping using a population of 110948 pregnancies. Among the safer screening strategies, the most cost-effective strategy was contingent screening with QF-PCR (CE ratio of $24084 per Down's syndrome (DS) detected). Using karyotyping, the CE ratio increased to $27898. QF-PCR missed only six clinically significant CA of which only one was expected to confer a high risk of an abnormal outcome. The incremental CE ratio (ICER) to find the CA missed by RAD was $66608 per CA. These costs are much higher than those involved for detecting DS cases. As the DSSP are mainly designed for DS detection, it may be relevant to question the additional costs of karyotyping.

Rapid aneuploidy testing versus traditional karyotyping in amniocentesis for certain referral indications

OBJECTIVE

(1) To determine the suitability of replacing full karyotype analysis with quantitative fluorescent polymerase chain reaction (QF-PCR) for prenatal diagnosis in amniotic fluid samples obtained by amniocentesis. (2) To evaluate an indication-based classification of cases at risk of missing clinically relevant chromosomal disorders by QF-PCR.

METHODS

We reviewed all fetal karyotypes obtained by amniocentesis between January 2004 and December 2008. We compared the cytogenetic findings obtained through conventional karyotype with those that would have been theoretically obtained using QF-PCR.

RESULTS

Of the 4007 karyotypes obtained, 110 abnormal karyotypes were found (2.8%). Out of these, 30 (27%) were chromosomal abnormalities (CA) which would not have been detected by PCR alone. These included 16 cases (53%) predicted to confer no increased risk, 9 (30%) predicted to have a low risk, and 5 (17%) with an uncertain or high risk of fetal abnormality. A policy of QF-PCR alone would have identified 80 of 85 (94%) clinically significant CA. When QF-PCR shows a normal result, the overall residual risk is 0.75% for any CA and 0.12% for a clinical significant CA.

CONCLUSION

In our population, a policy of QF-PCR alone would miss 0.12% clinically relevant CA. QF-PCR directed to common aneuploidies can be considered as an economically and clinically acceptable prenatal diagnosis policy, offering full karyotype only for specific indications.

Metaphase FISH on a chip: miniaturized microfluidic device for fluorescence in situ hybridization

Fluorescence in situ Hybridization (FISH) is a major cytogenetic technique for clinical genetic diagnosis of both inherited and acquired chromosomal abnormalities. Although FISH techniques have evolved and are often used together with other cytogenetic methods like CGH, PRINS and PNA-FISH, the process continues to be a manual, labour intensive, expensive and time consuming technique, often taking over 3 5 days, even in dedicated labs. We have developed a novel microFISH device to perform metaphase FISH on a chip which overcomes many shortcomings of the current laboratory protocols. This work also introduces a novel splashing device for preparing metaphase spreads on a microscope glass slide, followed by a rapid adhesive tape-based bonding protocol leading to rapid fabrication of the microFISH device. The microFISH device allows for an optimized metaphase FISH protocol on a chip with over a 20-fold reduction in the reagent volume. This is the first demonstration of metaphase FISH on a microfluidic device and offers a possibility of automation and significant cost reduction of many routine diagnostic tests of genetic anomalies.

Prenatal diagnosis of fetal aneuploidies: post-genomic developments

Prenatal diagnosis of fetal aneuploidies and chromosomal anomalies is likely to undergo a profound change in the near future. On the one hand this is mediated by new technical developments, such as chromosomal microarrays, which allow a much more precise delineation of minute sub-microscopic chromosomal aberrancies than the classical G-band karyotype. This will be of particular interest when investigating pregnancies at risk of unexplained development delay, intellectual disability or certain forms of autism. On the other hand, great strides have been made in the non-invasive determination of fetal genetic traits, largely through the analysis of cell-free fetal nucleic acids. It is hoped that, with the assistance of cutting-edge tools such as digital PCR or next generation sequencing, the long elusive goal of non-invasive prenatal diagnosis for fetal aneuploidies can finally be attained.

FlashFISH: "same day" prenatal diagnosis of common chromosomal aneuploidies

Fluorescence in situ hybridization (FISH) and quantitative fluorescence (QF)-PCR are rapid molecular methods that test for common chromosomal aneuploidies in prenatal diagnosis. While cytogenetic analysis requires approximately 7-14 days before fetal karyotypes are available, these molecular methods release results of sex chromosome aneuploidies, Down syndrome, Edward's syndrome, and Patau's syndrome within 24-48 h of fetal sampling, alleviating parental anxiety. However, specific diagnosis or exclusion of aneuploidy should be available within the same day of amniocentesis. We developed "FlashFISH," a low cost FISH method that allows accurate results to be reported within 2 h of fetal sampling. Here, we report our experience of using FlashFISH in prenatal diagnosis, and we illustrate in detail the protocols used for the purpose in our laboratory.

The selective use of rapid aneuploidy screening in prenatal diagnosis

AIMS

To evaluate the diagnostic utility and costing of the selective use of rapid aneuploidy screening (RAS) for chorion villus sampling (CVS) and amniocentesis specimens.

METHODS

CVS and amniocenteses performed between 2000 and 2006 were identified. Cases were subdivided into two groups: (i) RAS in addition to long-term culture and (ii) long-term chromosome culture alone. The frequency of RAS, the proportion of abnormal results and the cytogenetic costings were reviewed.

RESULTS

A total of 3315 procedures were performed: 730 CVS and 2585 amniocenteses. An abnormal karyotype culture was present in 366 of 3315 (11%). For CVS an abnormal culture was present in 164 (22.5%). RAS (short-term culture/direct preparation) was selectively used in 399 cases (54.6%) with an abnormal result in 128 (32% of RAS). For amniocentesis, 206 chromosome abnormalities were present (8.0% of specimens). RAS (interphase FISH) was selectively used in 580 amniocenteses (22.4%). FISH was requested in 95 (66.4%) of the 143 abnormal cases potentially detectable with standard probes. There was a progressive increase in utilisation of RAS for amniocentesis (8.9% in 2000 to 43.3% of cases in 2006, P < 0.001). CVS RAS was stable. This liberalisation resulted in a fourfold increase in expenditure for FISH and cost/abnormality detected ($A970 per abnormal result in 2000 to $A4015 per abnormal result in 2006).

CONCLUSION

The selective use of prenatal RAS results in a reasonably high detection rate for chromosomal anomalies. Liberalisation of RAS, however, is an expensive cytogenetic model. An approach based on some predictive level of risk combined with resource funding levels may be a more pragmatic approach.

[Preliminary application of MLPA-based array in detecting Y chromosome abnormalities]

To explore the feasibility and accuracy of MLPA-based array (Array-MLPA) in detecting sex chromosome abnormalities, MLPA probes were designed to target against three gene loci, TSPY (p11.2), PRY (q11), and RBMY (q11.2) in human Y chromosome. Array-MLPA approach was applied to test abnormalities of Y chromosome in 15 patient samples with known karyotypes. The data were compared with karyotyping and PCR analyses. The results showed that the copy number of each site detected by Array-MLPA was basically consistent with karyotyping analysis. Moreover, small deletions of chromosomes that were not found by routine karyotyping analysis were identified by the approach described, which fully agreed with PCR analysis, indicating that Array-MLPA was able to detect small abnormalities of chromosomes that cannot be found by karyotyping analysis. Compared to the routine karyotyping method, Array-MLPA has the advantages of high efficiency and reliability in chromosomal analysis, which has great potential in clinical application of diagnosis of chromosome abnormalities.

THE APPLICATION OF MICROARRAY BASED COMPARATIVE GENOMIC HYBRIDIZATION IN PRENATAL DIAGNOSIS

Microscopic forms of karyotyping and cytogenetic analysis by means of G-banded chromosome analysis and rapid FISH (fluorescencein situhybridization) on amniotic fluids or chorionic villus samples are at present regarded as the gold standard for prenatal diagnosis of chromosomal anomalies. Nevertheless, up to now the resolution of conventional chromosomal analysis was limited to approximately 4–5 Mb and not smaller than 2 Mb for FISH. Thus numerous common microdeletion syndromes are not detectable by conventional karyotyping. In addition, prenatal cells yield lower band resolution by conventional karyotyping than peripheral white blood cells making detection of subtle abnormalities even more difficult. With the advances in molecular-based techniques, a collaborative effort has led to the standardized method for detection of a restricted set of common chromosomal aneuploidies and microdeletion syndromes such as Down's syndrome, DiGeorge or Angelman syndrome either by rapid FISH and/or quantitative fluorescent PCR (QF-PCR). Even if the presence of particular phenotypic features of microdeletion or duplication syndromes may direct the use of syndrome-specific FISH tests in the postnatal period, syndrome-specific FISH analysis still has a very limited potential and application in the prenatal period due to the limitation in prenatal morphological or imaging diagnosis of many of the syndromes.

Resolution of trisomic mosaicism in prenatal diagnosis: estimated performance of a 50K SNP microarray

OBJECTIVE

To evaluate the ability of a DNA single nucleotide polymorphism (SNP) microarray to detect chromosome mosaicism for trisomy in prenatal samples in order to compare this with conventional cytogenetics.

METHOD

We created a dilution series of mock mosaic samples, by mixing measured amounts of fibroblast cells containing trisomy 8 from a male with aliquots of cells with a normal female karyotype. DNAs were extracted from these mosaic mixtures, then analysed on the Affymetrix 50K Xba SNP chip. Duplicate aliquots of each mosaic sample were probed using interphase FISH, with centromeric probes for chromosomes X, Y and 8, to estimate independently the proportion of male trisomy 8 in each sample. Data from the arrays were analysed using publicly available analysis tools. Statistical calculations were then performed using a Student's t-test to determine if there was a significant difference between the copy numbers of each chromosome.

RESULTS

These experiments using the Affymetrix 50K Xba SNP microarray showed mosaicism to be obvious at 20% and with additional statistical calculations, the lower limit for detection is about 10%.

CONCLUSION

The SNP microarray platform tested can detect mosaicism for trisomy in prenatal samples at levels comparable with conventional cytogenetic techniques in routine use.

Molecular cytogenetic and rapid aneuploidy detection methods in prenatal diagnosis

Cytogenetic analysis is an important component of prenatal diagnosis. The ability to rapidly detect aneuploidy and identify small structural abnormalities of fetal chromosomes has been greatly enhanced by the use of molecular cytogenetic technologies. In this review, we will present some of the molecular cytogenetic techniques available to the clinical cytogenetics laboratory. These include fluorescence in situ hybridization (FISH), quantitative fluorescence PCR (QF-PCR), multiplex ligation-dependent probe amplification (MLPA) and microarray-based comparative genomic hybridization (array CGH). The benefits and limitations of each technology will be discussed in the context of prenatal diagnosis.

Prenatal diagnosis of chromosomal abnormalities using array-based comparative genomic hybridization

PURPOSE

This study was designed to evaluate the feasibility of using a targeted array-CGH strategy for prenatal diagnosis of genomic imbalances in a clinical setting of current pregnancies.

METHODS

Women undergoing prenatal diagnosis were counseled and offered array-CGH (BCM V4.0) in addition to routine chromosome analysis. Array-CGH was performed with DNA directly from amniotic fluid cells with whole genome amplification, on chorionic villus samples with amplification as necessary, and on cultured cells without amplification.

RESULTS

Ninety-eight pregnancies (56 amniotic fluid and 42 CVS specimens) were studied with complete concordance between karyotype and array results, including 5 positive cases with chromosomal abnormalities. There was complete concordance of array results for direct and cultured cell analysis in 57 cases tested by both methods. In 12 cases, the array detected copy number variation requiring testing of parental samples for optimal interpretation. Array-CGH results were available in an average of 6 and 16 days for direct and cultured cells, respectively. Patient acceptance of array-CGH testing was 74%.

CONCLUSION

This study demonstrates the feasibility of using array-CGH for prenatal diagnosis, including reliance on direct analysis without culturing cells. Use of array-CGH should increase the detection of abnormalities relative to the risk, and is an option for an enhanced level of screening for chromosomal abnormalities in high risk pregnancies.

Rapid Prenatal Diagnosis by QF-PCR: Evaluation of 30,000 Consecutive Clinical Samples and Future Applications

Rapid prenatal diagnoses of major chromosome abnormalities can be performed on a large scale using highly polymorphic short tandem repeats (STRs) amplified by the quantitative fluorescent polymerase chain reaction (QF-PCR). The assay was introduced as a preliminary investigation to remove the anxiety of the parents waiting for the results by conventional cytogenetic analysis using amniotic fluid or chorionic cells. However, recent studies, on the basis of the analyses of several thousand samples, have shown that this rapid approach has a very high rate of success and could reduce the need for cytogenetic investigations. Its high efficiency, for example, allows early interruption of affected fetuses without the need of waiting for completion of fetal karyotype. The main advantages of the QF-PCR are its accuracy, speed, automation, and low cost that allows very large number of samples to be analyzed by few operators. Here, we report the results of using QF-PCR in a large series of consecutive clinical cases and discuss the possibility that, in a near future, it may even replace conventional cytogenetic analyses on selected samples.

Rapid Prenatal Diagnosis of Aneuploidy for Chromosomes 21, 18, 13, and X by Quantitative Fluorescence Polymerase Chain Reaction

OBJECTIVE

Quantitative fluorescence polymerase chain reaction (QF-PCR) is a rapid method for detection of chromosome copy number by amplification of repeat sequences at polymorphic loci. Our objective was to assess the performance of QF-PCR in detecting common aneuploidies in prenatal diagnosis.

STUDY DESIGN

The study group consisted of pregnant women referred for amniocentesis or chorionic villus sampling (CVS) due to increased risk of fetal aneuploidy. Samples were collected from known affected and normal pregnancies. These were blindly screened for trisomy of chromosomes 21, 18, 13, and sex chromosome abnormalities, using QF-PCR. DNA from uncultured amniocytes was directly extracted using a modified alkaline lysis method. DNA from CVS was extracted by the phenol-chloroform procedure. Ten short tandem repeat (STR) markers were used for detection of fetal aneuploidy and gender. The STRs were selected for high heterozygosity rates and efficiency of the PCR amplification. The forward primer of each pair was labeled with a unique fluorescent dye. Amplified products were detected by an ABI Prism 310 Genetic Analyzer and results were analyzed using GeneScan Analysis Software.

RESULTS

A total of 65 amniotic fluid and CVS samples were collected from affected and normal pregnancies. Two samples were contaminated with blood and were therefore excluded from the analysis. All 29 cases of aneuploidy were correctly diagnosed by QF-PCR, including 17 cases of trisomy 21, 7 cases of trisomy 18, and 5 cases with trisomy 13. The 34 normal samples were also correctly diagnosed as such. Thus, all results were in agreement with the standard cytogenetic results. There were no false-positive or false-negative results.

CONCLUSION

We conclude that QF-PCR is a rapid, reliable, and reproducible method that may be used to provide rapid results in prenatal diagnosis of aneuploidy.

Fetal nuchal translucency scan and early prenatal diagnosis of chromosomal abnormalities by rapid aneuploidy screening: observational study

OBJECTIVE

To investigate an approach for the analysis of samples obtained in screening for trisomy 21 that retains the advantages of quantitative fluorescent polymerase chain reaction (qf-PCR) over full karyotyping and maximises the detection of clinically significant abnormalities.

DESIGN

Observational study.

SETTING

Tertiary referral centre.

SUBJECTS

17,446 pregnancies, from which chorionic villous samples had been taken after assessment of risk for trisomy 21 by measurement of fetal nuchal translucency (NT) thickness at 11 to 13(+6) weeks of gestation.

INTERVENTIONS

Analysis of chorionic villous samples by full karyotyping and by qf-PCR for chromosomes 13, 18, 21, X, and Y.

MAIN OUTCOME MEASURE

Detection of clinically significant chromosomal abnormalities.

RESULTS

The fetal karyotype was normal in 15,548 (89.1%) cases and abnormal in 1898 (10.9%) cases, including 1722 with a likely clinically significant adverse outcome. Karyotyping all cases would lead to the diagnosis of all clinically significant abnormalities, and a policy of relying entirely on qf-PCR would lead to the diagnosis of 97.9% of abnormalities. An alternative strategy whereby qf-PCR is the main method of analysis and full karyotyping is reserved for those cases with a minimum fetal NT thickness of 4 mm would require full karyotyping in 10.1% of the cases, would identify 99.0% of the significant abnormalities, and would cost 60% less than full karyotyping for all.

CONCLUSIONS

In the diagnosis of chromosomal abnormalities after first trimester screening for trisomy 21, a policy of qf-PCR for all samples and karyotyping only if the fetal NT thickness is increased would reduce the economic costs, provide rapid delivery of results, and identify 99% of the clinically significant chromosomal abnormalities.

Quantitative Fluorescent Polymerase Chain Reaction versus Cytogenetics: Risk-Related Indication and Clinical Implication of Nondetected Chromosomal Disorders

BACKGROUND

The rapid detection of aneuploidies by quantitative fluorescent polymerase chain reaction (QF-PCR) allows reliable prenatal diagnosis of trisomies 21, 18, and 13. Discussion has been raised as to whether single QF-PCR could be an alternative to traditional cytogenetic karyotyping for certain referral categories.

OBJECTIVE

To evaluate an indication-based classification of cases at risk of missing clinically relevant chromosomal disorders by QF-PCR.

METHODS

From October 1999 to November 2003, 4,682 of 14,123 patients referred for amniocentesis decided to have QF-PCR as a rapid adjunct to conventional cytogenetic evaluation. Patients were classified according to the risk of missing chromosomal abnormalities by QF-PCR based on anamnestic risk and ultrasound prior to amniocentesis. The results in these two defined categories were compared in relation to the clinical significance of cytogenetic results.

RESULTS

QF-PCR and conventional cytogenetic analysis had concordant results in 4,617 of 4,682 (98.6%) cases. Thirty-six of 110 (32.2%) clinically significant chromosomal abnormalities were missed by QF-PCR. Patients classified not to be at risk of missing chromosomal abnormalities using QF-PCR had a residual risk of 1/166 (0.6%) for chromosomal distortions of clinical significance.

CONCLUSION

Classification by anamnestic and sonographic data does not specifically identify patients at risk of structural abnormalities. Clinical relevance of the nondetected anomalies essentially justifies traditional karyotyping regardless of risk classification.

Ultrasound findings before amniocentesis in selecting the method of analysing the sample

OBJECTIVE

To determine if the primary method of cytogenetic analysis in pregnant women undergoing amniocentesis should be quantitative fluorescent polymerase chain reaction (qf-PCR), with karyotyping being performed only on those with abnormal ultrasound findings.

METHODS

Amniocentesis was performed in 3854 cases. The median maternal age was 36 years and median gestational age was 18 weeks. The indication for karyotyping was an increased risk for aneuploidy in the absence or presence of sonographic abnormalities detected at the scan before amniocentesis. All samples were analysed by qf-PCR and full karyotyping. For each detectable fetal defect, the positive or negative likelihood ratio for aneuploidy was determined.

OUTCOME MEASURE

Detection rate of clinically significant chromosomal abnormalities.

RESULTS

The karyotype was normal in 3617 (93.9%) cases. In 237 (6.1%) cases, the karyotype was abnormal and the detection rate by qf-PCR was 92.4%. A policy of performing qf-PCR in all cases and karyotyping in only those with combined likelihood ratios of > 1, > 3, and > 5 would detect 98.3, 96.6, and 95.4% of all chromosomal abnormalities and would require karyotyping in 16.1, 8.0, and 5.4% of the cases, respectively.

CONCLUSIONS

More than 95% of the aneuploidies can be detected if karyotyping is performed in addition to qf-PCR in about 15% of the cases selected on the basis of ultrasound findings before amniocentesis.

Fetal reduction

Fetal Reduction has been employed over the past two decades as a mechanism to reduce the morbidity and mortality of multiple pregnancies. Utilization of the procedure has increased dramatically as IVF has become commonplace but the average starting number has decreased with the transfer of fewer embryos. Success rates from fetal reduction have improved as a function of increasing experience, better ultrasound, and lower starting numbers. Genetic diagnosis prior to reduction can improve the overall outcomes. Reduction of triplets or more clearly improves outcomes, and reduction of twins to a singleton is now a reasonable consideration.

Prenatal detection of Down's syndrome by rapid aneuploidy testing for chromosomes 13, 18, and 21 by FISH or PCR without a full karyotype: a cytogenetic risk assessment

BACKGROUND

In 2004, the UK National Screening Committee (UKNSC) recommended that new screening programmes for Down's syndrome need not include karyotyping and can offer prenatal diagnosis for the syndrome with FISH (fluorescence in-situ hybridisation) or PCR as rapid diagnostic tests. The UKNSC also recommended that FISH or PCR tests should only include trisomies 13, 18, and 21. We undertook a retrospective cytogenetic audit to assess the probable clinical effect of these proposed policy changes.

METHODS

23 prenatal cytogenetic laboratories from the UK public sector submitted data for amniotic fluid or chorionic villus samples referred from April, 1999, to March, 2004. We obtained data for the details of all abnormal karyotypes by reason for referral and assessed the efficiency of FISH and PCR rapid tests for the detection of chromosome abnormalities.

FINDINGS

Of 119,528 amniotic fluid and 23,077 chorionic villus samples, rapid aneuploidy testing replacement of karyotyping would have resulted in about one in 100 and one in 40 samples having an undetected abnormal karyotype, respectively. Of these missed results, 293 (30%) of 1006 amniotic fluid samples and 152 (45%) of 327 chorionic villus samples were associated with a substantial risk of an abnormal phenotypic outcome. Of 34,995 amniotic fluid and 3049 chorionic villus samples that had karyotyping and a rapid test on the same sample, none of the three technologies was completely reliable to detect an abnormal karyotype, but the best protocol for an interpretable result was PCR and karyotyping or FISH and karyotyping.

INTERPRETATION

Replacement of full karyotyping with rapid testing for trisomies 13, 18, and 21 after a positive screen for Down's syndrome will result in substantial numbers of liveborn children with hitherto preventable mental or physical handicaps, and represents a substantial change in the outcome quality of prenatal testing offered to couples in the UK.

Rapid detection of chromosomal aneuploidies in uncultured amniocytes by multiplex ligation-dependent probe amplification (MLPA)

OBJECTIVE

To test whether multiplex ligation-dependent probe amplification (MLPA) can be used for the detection of aneuploidy of chromosomes 13, 18, 21, X, and Y in uncultured amniocytes.

METHODS

We performed a prospective study based on 527 amniotic fluid samples. Chromosome copy numbers were determined by analysing the relative amount of PCR product of chromosome-specific MLPA probes. Results were available within 48 h and were compared with those of karyotyping.

RESULTS

There were 517 conclusive MLPA tests. In 514 tests, results were concordant with those of karyotyping. There were two cases of 69,XXX triploidy that could not be detected by MLPA and there was one false-positive result. Here, MLPA indicated a 47,XXY fetus, whereas the karyotype was 46,XY. We correctly identified all 23 cases of autosomal trisomy and the single case of monosomy X in samples collected from 16 up to 36 weeks of gestation. In 10 cases (2%), the result was inconclusive owing to an insufficient amount of DNA.

CONCLUSION

Sensitivity, specificity, and failure rate of MLPA were comparable to those of FISH and QF-PCR. Aneuploidy screening in uncultured amniocytes by MLPA is feasible in a clinical diagnostic setting, yielding an informative and rapid result in 98% of cases.

Update on selective reduction

Over the past 25 years fetal reduction has been utilized to reduce the risks of higher-order multiple pregnancies that have resulted from overly successful infertility therapies. The demographics of multiple pregnancy patients have evolved over the past decade, with increasing proportions coming from IVF as opposed to ovulation induction, being older and a higher proportion with donor eggs. Genetic diagnosis prior to reduction is becoming more common and is very safe in experienced hands. For all starting numbers, including twins, reduction to a lower number of fetuses reduces fetal losses, prematurity, and infant mortality and morbidity.

Role of FISH on Uncultured Amniocytes for the Diagnosis of Aneuploidies in the Presence of Fetal Anomalies

OBJECTIVE

To assess the accuracy of fluorescent in situ hybridization (FISH) on amniocytes in fetuses affected by structural malformations suggestive of chromosomal anomalies.

METHODS

FISH of uncultured amniotic fluid cells and conventional cytogenetic analysis were performed on 48 pregnancies with ultrasonographic (US) evidence of fetal anomalies. The AneuVysion assay (Vysis) with specific probes for chromosomes 13, 18, 21, X and Y, was used. Amniotic fluid samples were obtained between the 14th and 34th weeks of gestation.

RESULTS

In cases with a single abnormal US finding (n = 15), 5 aneuploidies were detected (1 case of trisomy 13 and 4 of trisomy 21). In the group with two or more malformations (n = 33) there were 15 aneuploidies (9 cases of trisomy 18, 2 of trisomy 21, 2 monosomy X, 1 trisomy 13, and 1 triploidy). In this group, conventional cytogenetic analysis revealed two additional chromosomal anomalies not detectable by FISH (1 trisomy 16 mosaic, and a terminal deletion 4p). No sex aneuploidies were observed.

CONCLUSIONS

The lack of false-positive diagnosis in the FISH analysis in our sample prompts us to consider interphase FISH as a useful tool in pregnancies at high risk for chromosomal aneuploidies. When FISH analysis is normal, the overall risk of chromosomal abnormalities is significantly reduced. However, the finding of two chromosomal anomalies undetectable by AneuVysion assay confirms the need for conventional chromosome analysis to complement FISH results. Moreover, the results collected here, in agreement with those already reported in the literature, indicate that FISH analysis on uncultured amniocytes can play an important role in counselling and decision-making, especially in cases at risk for aneuploidies, such as those with structural abnormalities at US.

Rapid prenatal diagnosis of common chromosome aneuploidies by QF-PCR. Assessment on 18 000 consecutive clinical samples

The quantitative fluorescent PCR (QF-PCR) assay, introduced during the last few years, allows prenatal diagnoses of common chromosome aneuploidies in a few hours after sampling. We report the first assessment of QF-PCR performed on a large cohort of 18,000 consecutive clinical specimens analysed in two different Centres. All samples were analysed by QF-PCR using several selected STR markers together with amelogenin and, occasionally, SRY for fetal sexing. Results were compared with those obtained by conventional cytogenetic analysis. In 17,129 tests, normal fetuses were detected by QF-PCR. No false positives were observed. All 732 cases of trisomy 21, 18, 13, triploidies, double trisomies as well as all but one fetuses with X and Y aneuploidies were correctly diagnosed. Chromosome mosaicism could also be suspected in several samples. In some cases of in vitro culture failures, QF-PCR was the only evidence of fetal X, Y, 21, 18 and 13 chromosome complement. QF-PCR proved to be efficient and reliable in detecting major numerical chromosome disorders. The main advantages of the molecular assay are its very low cost, speed and automation enabling a single operator to perform up to 40 assays per day. QF-PCR relieves anxiety of most parents within 24 h from sampling and accelerates therapeutic interventions in the case of an abnormal result. In countries where large scale conventional cytogenetics is hampered by its high cost and lack of technical expertise, QF-PCR may be used as the only prenatal diagnostic test.

Do reduced multiples do better?

Dramatic successes in infertility care have allowed millions of previously fertile women to have their own children. However, an epidemic of multiple pregnancies has resulted, with catastrophic increases in morbidity and mortality, and in the economic costs to society. Multifetal pregnancy reduction (MFPR) has been used to decrease fetal number in the late first trimester and has dramatically improved outcomes. Recent data suggest that pregnancies starting with three or four, and in some cases five fetuses, which are reduced to twins, do as well as starting with twins. Patients with triplets do better reduced to twins. Reduction to a singleton is becoming more common, particularly for women over 40. Combining MFPR with chorionic villus sampling in patients over 30 years of age has enabled couples to maximize the health of the resultant children.

Provision of genetic services in Europe: current practices and issues

This paper examines the professional and scientific views on the social, ethical and legal issues that impact on the provision of genetic services in Europe. Many aspects have been considered, such as the definition and the aims of genetic services, their organization, the quality assessment, public education, as well as the partnership with patients support groups and the multicultural aspects. The methods was primarily the analysis of professional guidelines, legal frameworks and other documents related to the organization of genetic services, mainly from Europe, but also from USA and international organizations. Then, the method was to examine the background data emerging from an updated report produced by the Concerted Action on Genetic Services in Europe, as well as the issues debated by 43 experts from 17 European countries invited to an international workshop organized by the European Society of Human Genetics Public and Professional Policy Committee in Helsinki, Finland, 8 and 9 September 2000. Some conclusions were identified from the ESHG workshop to arrive at outlines for optimal genetic services. Participants were concerned about equal accessibility and effectiveness of clinical genetic services, quality assessment of services, professional education, multidisciplinarity and division of tasks as well as networking. Within European countries, adherence to the organizational principles of prioritization, regionalization and integration into related health services would maximize equal accessibility and effectiveness of genetic actions. There is a need for harmonization of the rules involved in financial coverage of DNA tests in order to make these available to all Europeans. Clear guidelines for the best practice will ensure that the provision of genetic services develops in a way that is beneficial to its customers, be they health professionals or the public, especially since the coordination of clinical, laboratory and research perspectives within a single organizational structure permits a degree of coherence not often found in other specialties.

Prenatal diagnosis by rapid aneuploidy detection and karyotyping: a prospective study of the role of ultrasound in 1589 second-trimester amniocenteses

BACKGROUND

Reliable methods are available for rapid aneuploidy detection (RAD) for the prenatal diagnosis of trisomies 21, 18 and 13. This study examines the potential advantages and limitations of using RAD as a replacement rather than as an adjunct to traditional karyotyping.

METHODS

One thousand five hundred and eighty-nine consecutive pregnancies referred for cytogenetic assessment were offered RAD (FISH or QF-PCR) as an adjunct to traditional karyotyping. The results of these two processes were compared, and the effects of three policies for cytogenetic evaluation were determined: RAD alone, a combination of RAD for all and traditional karyotyping for cases with ultrasound anomalies or a policy of RAD and traditional karyotyping in all cases.

RESULTS

RAD was uninformative because of maternal-cell contamination in 37 (2.3%) cases compared to 4 (0.3%) cases of culture failure in traditional karyotyping. RAD and traditional karyotyping results were concordant in 1526 of 1548 (98.6%) cases. All non-mosaic cases of trisomies 21, 18 and 13 and cases of triploidy were correctly identified by RAD, and there were no false-positive diagnoses. The gold standard of a traditional karyotype in each case would have detected all chromosomal abnormalities. A policy of RAD alone would have identified 60 of 73 (82%) clinically important chromosomal abnormalities. The addition of a full karyotype for cases with evidence of ultrasound abnormalities would have improved detection to 95%.

CONCLUSION

A policy offering RAD to all patients, but restricting traditional karyotyping to cases with ultrasound anomalies, would reduce the number of traditional karyotypes requested by 70%, but maintain a 95% detection rate for all clinically important chromosomal abnormalities. Further studies are required to determine whether similar results could be obtained in district general hospital units and to determine whether this approach would be acceptable to health professionals and patients.

Rapid prenatal diagnosis in translocation carriers by interphase FISH with chromosome-specific subtelomere probes

Interphase fluorescence in situ hybridization (FISH) analysis can provide rapid preliminary analysis of chromosome aneuploidy from direct amniocyte and chorionic villus sample (CVS) preparations. Typically, interphase FISH is used in screening for numerical abnormalities of chromosomes X, Y, 13, 18, and 21. More recently, FISH probe sets became available for the subtelomeric region of each chromosome, allowing screening for terminal chromosome rearrangements. The purpose of the current study was to evaluate the use of dual-color interphase FISH analysis with chromosome-specific subtelomere probes for rapid prenatal diagnosis in 14 pregnancies from 12 different translocation carriers. Interphase FISH analysis was performed on direct CVS or amniocyte preparations from 12 reciprocal translocation and two Robertsonian translocation pregnancies with the appropriate chromosome-specific subtelomere probes for each chromosome involved in the translocation. Analysis of the interphase FISH probe signals predicted balanced or normal segregants in each case, thus rapidly excluding a chromosomally unbalanced segregant. Subsequent metaphase analysis showed normal karyotypes in seven fetuses and balanced translocations in the remaining seven. This series illustrates the utility of interphase FISH analysis with chromosome-specific subtelomere probes for rapid prenatal diagnosis in cases of parental reciprocal translocations and Robertsonian translocations.

Residual risk for cytogenetic abnormalities after prenatal diagnosis by interphase fluorescence in situ hybridization (FISH)

Results from conventional cytogenetic studies on 21 609 amniotic fluid specimens were analyzed retrospectively to determine the residual risk for a cytogenetic abnormality if interphase FISH, capable of only detecting aneuploidy for chromosomes 13, 18, 21, X and Y, was performed and did not reveal an abnormality. Detection rates (the probability of detecting a cytogenetic abnormality when an abnormality is present) and residual risks (the likelihood of a cytogenetic abnormality, in view of normal interphase FISH results) were calculated for the four major clinical indications for prenatal diagnosis (advanced maternal age, abnormal maternal serum screen indicating increased risk for trisomy 18 or trisomy 21, abnormal maternal serum screen indicating increased risk for neural tube defects and ultrasound abnormality). Differences in detection rates were observed to depend on clinical indication and presence or absence of ultrasound abnormalities. The detection rate ranged from 18.2 to 82.6% depending on the clinical indication. The detection rates of abnormalities significant to the pregnancy being evaluated (i.e. abnormalities excluding familial balanced rearrangements and familial markers) were between 28.6 and 86.4%. The presence of ultrasound abnormalities increased the detection rate from 72.2 to 92.5% for advanced maternal age and from 78.6 to 91.3% for abnormal maternal serum screen, indicating increased risk for trisomy 18 or trisomy 21. With regard to residual risk, the risk for a clinically significant abnormality decreased from 0.9-10.1%, prior to the interphase FISH assay, to a residual risk of 0.6-1.5% following a normal interphase FISH result in the 4 groups studied. Providing patients with detection rates and residual risks, most relevant to their situation (clinical indication and presence or absence of ultrasound abnormality) during counseling, could help them better understand the advantages and limitations of interphase FISH in their prenatal diagnostic evaluation.

Selective reduction

Multifetal pregnancy reduction continues to be controversial. Attitudes about MFPR have not, in our experience, followed a simple "pro-choice/pro-life" dichotomy. As far back as the mid to late 1980s, opinions about the subject were varied. Even then, when much less was known about the subject, opinions did not always parallel the usual pro-choice/theological boundaries. We believe that the real debate over the next 5 to 10 years will not be whether or not MFPR should be performed with triplets or more. The fact is that MFPR does improve those outcomes. A serious debate will emerge over whether or not it is appropriate to offer MFPR routinely for twins, even natural ones, for whom the outcome is commonly considered "good enough." Our data suggest that reduction of twins to a singleton improves the outcome of the remaining fetus. No consensus on appropriateness of routine 2-1 reductions is ever likely to emerge. The ethical issues surrounding MFPR will always be controversial. Over the years, much has been written on the subject. Opinions will always vary from outraged condemnation to complete acceptance. No short paragraph could do justice to the subject other than to state that most proponents do not believe this is a frivolous procedure but do believe in the principle of proportionality ie, therapy to achieve the most good for the least harm). Over the past 15 years, MFPR has become a well-established and integral part of infertility therapy and attempts to deal with the sequelae of aggressive infertility management. In the mid 1980s, the risks and benefits of the procedure could only be guessed. We now have clear and precise data on the risks and benefits of the procedure and an understanding that the risks increase substantially with the starting and finishing number of fetuses in multifetal pregnancies. The collaborative loss rate numbers (ie, 4.5% for triplets, 8% for quadruplets. 11% for quintuplets, and 15% for sextuplets or more) seem reasonable to present to patients for the procedure performed by an experienced operator. Our experiences and anecdotal experiences from other groups suggest that less experienced operators have worse outcomes. Pregnancy loss is not the only poor outcome. The other main issue with which to be concerned is very early premature delivery, where there is an increasing rate of poor outcomes correlated with the starting number. The finishing numbers are also critical, with twins having the best outcomes for cases starting with three or more. Triplets and singletons do not do as well. We hope that MFPR will become obsolete as better control of ovulation agents and assisted reproductive technologies make multifetal pregnancies uncommon.

Simple technique of codenaturation and fluorescence in situ hybridization with probes in a microcamera

We describe a rapid, precise and economical method of performing fluorescence in situ hybridization with probes in a microcamera, without chemical risk for the operator caused by the use of formamide. The application has been tried on metaphase spreads and interphase nuclei from peripheral blood or bone marrow cultures and on formalin-fixed, paraffin-embedded tissue.

Prenatal diagnosis: molecular genetics and cytogenetics

The technologies developed for the Human Genome Project, the recent surge of available DNA sequences resulting from it and the increasing pace of gene discoveries and characterization have all contributed to new technical platforms that have enhanced the spectrum of disorders that can be diagnosed prenatally. The importance of determining the disease-causing mutation or the informativeness of linked genetic markers before embarking upon a DNA-based prenatal diagnosis is, however, still emphasized. Different fluorescence in situ hybridization (FISH) technologies provide increased resolution for the elucidation of structural chromosome abnormalities that cannot be resolved by more conventional cytogenetic analyses, including microdeletion syndromes, cryptic or subtle duplications and translocations, complex rearrangements involving many chromosomes, and marker chromosomes. Interphase FISH and the quantitative fluorescence polymerase chain reaction are efficient tools for the rapid prenatal diagnosis of selected aneuploidies, the latter being considered to be most cost-effective if analyses are performed on a large scale. There is some debate surrounding whether this approach should be employed as an adjunct to karyotyping or whether it should be used as a stand-alone test in selected groups of women.

French multi-centric study of 2000 amniotic fluid interphase FISH analyses from high-risk pregnancies and review of the literature

This prospective and multi-centric study confirms the accuracy and the limitations of interphase FISH and shows that any cytogenetics laboratory can perform this technique. With regard to the technical approach, we think that slides must be examined by two investigators, because the scoring may be subjective. The main problem with the AneuVysion kit concerns the alpha satellite probes, and especially the chromosome 18 probe, which is sometimes very difficult to interpret because of the high variability of the size of the spots, and this may lead to false negative and uninformative cases. The best solution would be to replace these probes by locus-specific probes. Concerning clinical management, we offer interphase FISH only in very high-risk pregnancies or/and at late gestational age because of the cost of the test. We think that an aberrant FISH result can be used for a clinical decision when it is associated with a corresponding abnormal ultrasound scan. In other cases, most of the time, we prefer to wait for the standard karyotype.

Prenatal detection of aneuploidies using fluorescence in situ hybridization: a preliminary experience in an Indian set up

Fluorescence in situ hybridization (FISH) is a powerful molecular cytogenetic technique which allows rapid detection of aneuploidies on interphase cells and metaphase spreads. The aim of the present study was to evaluate FISH as a tool in prenatal diagnosis of aneuploidies in high risk pregnancies in an Indian set up. Prenatal diagnosis was carried out in 88 high-risk pregnancies using FISH and cytogenetic analysis. Multicolour commercially available FISH probes specific for chromosomes 13, 18, 21, X and Y were used. Interphase FISH was done on uncultured cells from chorionic villus and amniotic fluid samples. FISH on metaphase spreads was done from cord blood samples. The results of FISH were in conformity with the results of cytogenetic analysis in all the normal and aneuploid cases except in one case of structural chromosomal abnormality. The hybridization efficiency of the 5 probes used for the detection of aneuploidies was 100%. Using these probes FISH assay yielded discrete differences in the signal profiles between cytogenetically normal and abnormal samples. The overall mean interphase disomic signal patterns of chromosomes 13, 18, 21, X and Y were 94.45%; for interphase trisomic signal pattern of chromosome 21 was 97.3%. Interphase FISH is very useful in urgent high risk cases. The use of FISH overcomes the difficulties of conventional banding on metaphase spreads and reduces the time of reporting. However, with the limited number of probes used, the conventional cytogenetic analysis serves as a gold standard at present. It should be employed as an adjunctive tool to conventional cytogenetics.