Continued Validation of Ultrasound Guidance Targeting Tasks: Relationship with Procedure Performance

RATIONALE AND OBJECTIVES

To determine if deliberative practice with novel ultrasound guidance targeting tasks improves simulated procedural skill.

MATERIALS AND METHODS

In a nonrandomized interventional trial first year medical students practiced the previous described dowel and straw targeting tasks 1 hour a week for 4 weeks (training group) or had no training (controls). Afterward, they each performed a simulated amniocentesis (AMN) and chorionic villus sampling (CVS) procedure. Procedures were scored using a global rating scale (GRS) and compared between groups with Mann-Whitney U tests. Two-way random effects intraclass correlation coefficients for the inter- and intra-rater variability were calculated for each item in both GRS's.

RESULTS

The training group (n = 22) had higher scores on several aspects and overall performance of AMN compared to controls (n = 15). There were no differences between groups for CVS. The inter-rater and intra-rater reliability of the GRS's for both AMN and CVS ranged from 0.16 to 0.89 with most values demonstrating good to excellent agreement.

CONCLUSION

This study demonstrates validity evidence in the content and internal structure domains for the AMN and CVS simulators and their accompanying GRS's. Repetitive practice of the targeting tasks improved student performance in simulated AMN, but modifications are needed for it to be relevant to other procedures such as CVS.

Accurate fetal variant calling in the presence of maternal cell contamination

High-throughput sequencing of fetal DNA is a promising and increasingly common method for the discovery of all (or all coding) genetic variants in the fetus, either as part of prenatal screening or diagnosis, or for genetic diagnosis of spontaneous abortions. In many cases, the fetal DNA (from chorionic villi, amniotic fluid, or abortive tissue) can be contaminated with maternal cells, resulting in the mixture of fetal and maternal DNA. This maternal cell contamination (MCC) undermines the assumption, made by traditional variant callers, that each allele in a heterozygous site is covered, on average, by 50% of the reads, and therefore can lead to erroneous genotype calls. We present a panel of methods for reducing the genotyping error in the presence of MCC. All methods start with the output of GATK HaplotypeCaller on the sequencing data for the (contaminated) fetal sample and both of its parents, and additionally rely on information about the MCC fraction (which itself is readily estimated from the high-throughput sequencing data). The first of these methods uses a Bayesian probabilistic model to correct the fetal genotype calls produced by MCC-unaware HaplotypeCaller. The other two methods "learn" the genotype-correction model from examples. We use simulated contaminated fetal data to train and test the models. Using the test sets, we show that all three methods lead to substantially improved accuracy when compared with the original MCC-unaware HaplotypeCaller calls. We then apply the best-performing method to three chorionic villus samples from spontaneously terminated pregnancies.

Amniocentesis and chorionic villus sampling for prenatal diagnosis

BACKGROUND

During pregnancy, fetal cells suitable for genetic testing can be obtained from amniotic fluid by amniocentesis (AC), placental tissue by chorionic villus sampling (CVS), or fetal blood. A major disadvantage of second trimester amniocentesis is that the results are available relatively late in pregnancy (after 16 weeks' gestation). Earlier alternatives are chorionic villus sampling (CVS) and early amniocentesis, which can be performed in the first trimester of pregnancy.

OBJECTIVES

The objective of this review was to compare the safety and accuracy of all types of AC (i.e. early and late) and CVS (e.g. transabdominal, transcervical) for prenatal diagnosis.

SEARCH METHODS

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (3 March 2017), ClinicalTrials.gov, the WHO International Clinical Trials Registry Platform (ICTRP; 3 March 2017), and reference lists of retrieved studies.

SELECTION CRITERIA

All randomised trials comparing AC and CVS by either transabdominal or transcervical route.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trials for inclusion and risk of bias, extracted data and checked them for accuracy. The quality of the evidence was assessed using the GRADE approach.

MAIN RESULTS

We included a total of 16 randomised studies, with a total of 33,555 women, 14 of which were deemed to be at low risk of bias. The number of women included in the trials ranged from 223 to 4606.Studies were categorized into six comparisons: 1. second trimester AC versus control; 2. early versus second trimester AC; 3. CVS versus second trimester AC; 4. CVS methods; 5. Early AC versus CVS; and 6. AC with or without ultrasound.One study compared second trimester AC with no AC (control) in a low risk population (women = 4606). Background pregnancy loss was around 2%. Second trimester AC compared to no testing increased total pregnancy loss by another 1%. The confidence intervals (CI) around this excess risk were relatively large (3.2% versus 2.3 %, average risk ratio (RR) 1.41, 95% CI 0.99 to 2.00; moderate-quality evidence). In the same study, spontaneous miscarriages were also higher (2.1% versus 1.3%; average RR 1.60, 95% CI 1.02 to 2.52; high-quality evidence). The number of congenital anomalies was similar in both groups (2.0% versus 2.2%, average RR 0.93, 95% CI 0.62 to 1.39; moderate-quality evidence).One study (women = 4334) found that early amniocentesis was not a safe early alternative compared to second trimester amniocentesis because of increased total pregnancy losses (7.6% versus 5.9%; average RR 1.29, 95% CI 1.03 to 1.61; high-quality evidence), spontaneous miscarriages (3.6% versus 2.5%, average RR 1.41, 95% CI 1.00 to 1.98; moderate-quality evidence), and a higher incidence of congential anomalies, including talipes (4.7% versus 2.7%; average RR 1.73, 95% CI 1.26 to 2.38; high-quality evidence).When pregnancy loss after CVS was compared with second trimester AC, there was a clinically significant heterogeneity in the size and direction of the effect depending on the technique used (transabdominal or transcervical), therefore, the results were not pooled. Only one study compared transabdominal CVS with second trimester AC (women = 2234). They found no clear difference between the two procedures in the total pregnancy loss (6.3% versus 7%; average RR 0.90, 95% CI 0.66 to 1.23, low-quality evidence), spontaneous miscarriages (3.0% versus 3.9%; average RR 0.77, 95% CI 0.49 to 1.21; low-quality evidence), and perinatal deaths (0.7% versus 0.6%; average RR 1.18, 95% CI 0.40 to 3.51; low-quality evidence). Transcervical CVS may carry a higher risk of pregnancy loss (14.5% versus 11.5%; average RR 1.40, 95% CI 1.09 to 1.81), but the results were quite heterogeneous.Five studies compared transabdominal and transcervical CVS (women = 7978). There were no clear differences between the two methods in pregnancy losses (average RR 1.16, 95% CI 0.81 to 1.65; very low-quality evidence), spontaneous miscarriages (average RR 1.68, 95% CI 0.79 to 3.58; very low-quality evidence), or anomalies (average RR 0.68, 95% CI 0.41 to 1.12; low-quality evidence). We downgraded the quality of the evidence to low due to heterogeneity between studies. Transcervical CVS may be more technically demanding than transabdominal CVS, with more failures to obtain sample (2.0% versus 1.1%; average RR 1.79, 95% CI 1.13 to 2.82, moderate-quality evidence).Overall, we found low-quality evidence for outcomes when early amniocentesis was compared to transabdominal CVS. Spontaneous miscarriage was the only outcome supported by moderate-quality evidence, resulting in more miscarriages after early AC compared with transabdominal CVS (2.3% versus 1.3%; average RR 1.73, 95% CI 1.15 to 2.60). There were no clear differences in pregnancy losses (average RR 1.15, 95% CI 0.86 to 1.54; low-quality evidence), or anomalies (average RR 1.14, 95% CI 0.57 to 2.30; very low-quality evidence).We found one study that examined AC with or without ultrasound, which evaluated a type of ultrasound-assisted procedure that is now considered obsolete.

AUTHORS' CONCLUSIONS

Second trimester amniocentesis increased the risk of pregnancy loss, but it was not possible to quantify this increase precisely from only one study, carried out more than 30 years ago.Early amniocentesis was not as safe as second trimester amniocentesis, illustrated by increased pregnancy loss and congenital anomalies (talipes). Transcervical chorionic villus sampling compared with second trimester amniocentesis may be associated with a higher risk of pregnancy loss, but results were quite heterogeneous.Diagnostic accuracy of different methods could not be assessed adequately because of incomplete karyotype data in most studies.

[Maternal cell contamination of prenatal samples and the potential effects on prenatal diagnosis results]

OBJECTIVE

To assess the frequency and significance of maternal cell contamination (MCC) in the invasive prenatal diagnosis, and to analysis the MCC effect on prenatal diagnosis results.

METHODS

Totally 519 amniotic fluid samples from second trimester pregnancy, 57 chorionic villus samples from first trimester pregnancy, and 576 blood samples from corresponded pregnant women were collected and genotyped by Promega PowerPlex 16 system. MCC was determined according to the genotyping results. Karyotypic and molecular diagnosis results were contrasted between MCC and non-MCC specimen of the same fetal.

RESULTS

MCC presented in 3.1% (16/519) uncultured amniotic fluid, 1.3% (7/519) cultured amniotic fluid and 5% (3/57) villi specimens. In the study of fetal karyotype, MCC had no significant effect on normal female fetus; but for male fetus and abnormal female fetus, there were risk of erroneous results of mosaics. As to molecular diagnosis, MCC resulted in more complex effects for the different diagnostic methods. And 10%MCC had led to misdiagnosis.

CONCLUSIONS

For the prenatal cytogenetic tests, MCC should be excluded when there were mosaicism karyotype results or suspicious MCC of chorionic villi samples. The effects of MCC had more seriously impact on prenatal molecular testing, which suggesting the recommend regular identity test for MCC should be carried out.

Quality aspects of prenatal cytogenetic diagnosis: determining the effect of various factors involved in handling amniotic fluid and chorionic villus material for cytogenetic diagnosis

OBJECTIVES

To investigate the effect of factors involved in cell culturing and slide preparation of amniotic fluid (AF) and chorionic villus biopsies (CVB) for prenatal cytogenetic diagnosis.

METHODS

The effect on the outcome of our standard AF cell culture procedure of volume and appearance of the submitted AF specimen, gynaecologist performing the amniocentesis, week of gestation in which the specimen was taken and culture medium was retrospectively investigated. In a prospective study controlled experimental variation was introduced in composition of fixative, relative humidity, temperature and airflow during slide preparation from primary CVB and AF in situ cultures. For evaluation, analysis of regression or variance was used.

RESULTS

Provided that at least 0.8 mL AF per culture dish was admitted, none of the investigated factors appeared as critical resulting in unacceptable variation in outcome. Variation in appearance of the AF had a relatively major impact: bloody or brown AF resulted in a 3 days longer culture time. To a limited degree, metaphase quality of AF and CVB cells was affected by composition of fixative, relative humidity, ambient temperature and airflow during slide preparation.

CONCLUSION

Current prenatal cytogenetic practice as described here appears in general to be robust and reliable. The investigated conditions are not critical within the investigated range. Expensive measures for fine control of these conditions are, therefore, not required.

(Potential) false-negative diagnoses in chorionic villi and a review of the literature

OBJECTIVES

To assess the incidence of (potential) false-negative findings of cytogenetic diagnosis in STC-villi and/or LTC-villi and to determine the best strategy for karyotyping chorionic villi in order to avoid false-negative results.

METHODS

2476 chorionic villus samples were received for prenatal cytogenetic investigations. Karyotyping was routinely performed on STC- and LTC-villi preparations by G-banding. Fluorescence in situ hybridization (FISH) analyses were performed in addition to standard chromosome analysis when necessary. Sometimes follow-up investigations like amniocentesis were performed before a definite prenatal cytogenetic result could be reported.

RESULTS

In 2389/2476 (96.5%) of the cases, both STC- and LTC-villi were investigated. Normal STC- with abnormal LTC-villi results and finally an abnormal fetal karyotype were detected in ten cases (10/2389; 0.42%); in 9/10 of the cases the indication was fetal ultrasound abnormalities. Normal STC- and LTC-villi and finally an abnormal fetal karyotype were detected in two cases (2/2389; 0.08%).

CONCLUSION

The most reliable technique for prenatal diagnosis after chorionic villus sampling (CVS) is the combination of the analysis of both STC- and LTC-villi to reduce the incidence of false-negative findings to a minimum. In the case of fetal ultrasound abnormalities with a small amount of villi available, the investigation of LTC-villi is recommended over that of STC-villi.

A randomised controlled trial of biopsy forceps and cannula aspiration for transcervical chorionic villus sampling

OBJECTIVE

This trial compared two instruments for transcervical chorionic villus sampling (CVS).

DESIGN

Randomised controlled trial.

SETTING

Regional university prenatal diagnosis and treatment centre.

POPULATION

Two hundred women were randomised at 10(+0)-12(+6) weeks of gestation to transcervical CVS using cannula aspiration (CA) or biopsy forceps (BF).

METHODS

Women undergoing indicated CVS signed informed consent. Randomisation after decision to perform transcervical CVS.

MAIN OUTCOME MEASURES

PRIMARY OUTCOME

the rise in maternal serum alpha-fetoprotein (alpha-FP).

SECONDARY OUTCOMES

(i) placental trauma (fetomaternal haemorrhage [FMH]); (ii) laboratory, procedure, and cytogenetic results and pregnancy outcomes; (iii) patient and operator satisfaction; and (iv) economic analyses. Analyses were performed by intention to treat.

RESULTS

The -FP rise did not differ between groups; there was no other evidence of placental trauma. BF were better tolerated by women, provided culturable tissue, after fewer instrument passes, with greater ease and in less time. BF were associated with cost savings.

CONCLUSIONS

Unlike -FP, other markers of FMH were unaltered, questioning the reliability of alpha-FP as an indicator of FMH. Compared with CA, transcervical BF caused comparable placental trauma, appeared to be similarly effective and safe and were preferred by operators and patients.

Chorionic villus sampling and amniocentesis

PURPOSE OF REVIEW

The advantages and disadvantages of common invasive methods for prenatal diagnosis are presented in light of new investigations.

RECENT FINDINGS

Several aspects of first-trimester chorionic villus sampling and mid-trimester amniocentesis remain controversial, especially fetal loss rate, feto-maternal complications, and the extension of both sampling methods to less traditional gestational ages (early amniocentesis, late chorionic villus sampling), all of which complicate genetic counseling. A recent randomized trial involving early amniocentesis and late chorionic villus sampling has confirmed previous studies, leading to the unquestionable conclusion that transabdominal chorionic villus sampling is safer. The old dispute over whether limb reduction defects are caused by chorionic villus sampling gains new vigor, with a paper suggesting that this technique has distinctive teratogenic effects. The large experience involving maternal and fetal complications following mid-trimester amniocentesis allows a better estimate of risk for comparison with chorionic villus sampling.

SUMMARY

Transabdominal chorionic villus sampling, which appears to be the gold standard sampling method for genetic investigations between 10 and 15 completed weeks, permits rapid diagnosis in high-risk cases detected by first-trimester screening of aneuploidies. Sampling efficiency and karyotyping reliability are as high as in mid-trimester amniocentesis with fewer complications, provided the operator has the required training, skill and experience.

Maternal cell contamination of prenatal samples assessed by QF-PCR genotyping

OBJECTIVES

To establish the genotype of cultured cells from a cohort of amniotic fluid and chorionic villus samples, and compare this genotype with that obtained from uncultured material from the same sample, in order to assess the frequency and significance of maternal cell contamination of prenatal samples.

METHODS

Quantitative fluorescence-polymerase chain reaction (QF-PCR) was carried out by amplification of microsatellite markers using fluorescence-labelled primers, followed by quantitative analysis of the allele peaks on a genetic analyser. A multiplex of 12 primer pairs for four loci on each of chromosomes 13, 18 and 21 was used.

RESULTS

A total of 307 prenatal samples were tested. Of the 254 amniotic fluid samples, 39.8% had some degree of bloodstaining, ranging from 5% bloodstaining in the cell pellet to heavily bloodstained fluid. Uncultured samples were tested by QF-PCR analysis and the cultured cells were tested by both QF-PCR and karyotype analysis. Of the samples, 90.2% had the same single genotype on direct and cultured material. Two samples (0.65%) were mosaic for an aneuploidy cell line. A second genotype, interpreted as maternal cell contamination, was identified in direct and/or cultured preparations in 9.1% of samples, 17.8% of which were not bloodstained. Seven amniotic fluid samples (2.8%) showed maternal cell contamination in cultured material.

CONCLUSIONS

For heavily bloodstained amniotic fluid samples, a maternal blood specimen may help interpret the results of rapid trisomy testing, followed by confirmation of the fetal origin of cultured cells. QF-PCR analysis has established a higher incidence of maternal cell contamination of cultured amniocytes than previous reports; the presence of MCC (maternal cell contamination) in cultured cells from samples with no bloodstaining underlines the need for karyotype analysis of more than one XX culture.

Prenatal genetic testing by amniocentesis appears to result in a lower risk of fetal loss than chorionic villus sampling in singleton pregnancies achieved by intracytoplasmic sperm injection

OBJECTIVE

To compare pregnancy outcome after prenatal genetic testing by chorionic villus sampling (CVS) or amniocentesis in singleton pregnancies achieved by intracytoplasmic sperm injection (ICSI).

DESIGN

Retrospective analysis.

SETTING

Tertiary referral center.

PATIENT(S)

Eight hundred twenty-eight patients with singleton gestations achieved by ICSI.

INTERVENTION(S)

Midtrimester amniocentesis (685 patients) and first-trimester CVS (143 patients).

MAIN OUTCOME MEASURE(S)

Fetal loss rate, preterm delivery rate, and proportion of babies born with low or very low birth weight.

RESULT(S)

A significant difference was observed in fetal loss rate between CVS and amniocentesis (3.7% vs. 0.9%, respectively). On the other hand, a similar preterm delivery rate was present between the two methods (11.2% vs. 12.4%, respectively). No significant difference was observed between amniocentesis and CVS in the proportion of babies with birth weight of either <1,500 g (1.8% vs. 3.8%, respectively) or between 1,500 and 2,500 g (8.2% vs. 4.6%, respectively).

CONCLUSION(S)

Amniocentesis appears to result in a lower risk of fetal loss as compared with CVS in patients with a singleton pregnancy achieved by ICSI.

Amniocentesis and chorionic villus sampling for prenatal diagnosis

BACKGROUND

A major disadvantage of second trimester amniocentesis is that the result is usually available only after 18 weeks' gestation. Chorionic villus sampling (CVS) and early amniocentesis can be done between 9 and 14 weeks and offer an earlier alternative.

OBJECTIVES

The objective was to assess comparative safety and accuracy of second trimester amniocentesis, early amniocentesis, transcervical and transabdominal CVS.

SEARCH STRATEGY

We searched the Cochrane Pregnancy and Childbirth Group trials register (March 2003) and the Cochrane Central Register of Controlled Trials (The Cochrane Library, Issue 1, 2002).

SELECTION CRITERIA

All randomised trials comparing amniocentesis and CVS.

DATA COLLECTION AND ANALYSIS

Two reviewers assessed eligibility and trial quality and performed data extraction. We analysed the data using RevMan software.

MAIN RESULTS

A total of 14 randomised studies have been included. In a low risk population with a background pregnancy loss of around 2%, a second trimester amniocentesis will increase this risk by another 1%. This difference did not reach statistical significance, but the increase in spontaneous miscarriages following second trimester amniocentesis compared with controls (no amniocentesis) did (2.1% versus 1.3%; relative risk (RR) 1.02 to 2.52). Early amniocentesis is not a safe early alternative to second trimester amniocentesis because of increased pregnancy loss (7.6% versus 5.9%; RR 1.29, 95% CI 1.03 to 1.61) and higher incidence of talipes compared to CVS (1.8% versus 0.2%; RR 6.43, 95% CI 1.68 to 24.64).Compared with second trimester amniocentesis, transcervical CVS carries a significantly higher risk of pregnancy loss (14.5% versus 11%; RR 1.40, 95% CI 1.09 to 1.81) and spontaneous miscarriage (12.9% versus 9.4%; RR 1.50, 95% CI 1.07 to 2.11). One study compared transabdominal CVS with second trimester amniocentesis and found no significant difference in the total pregnancy loss between the two procedures (6.3% versus 7%). Transcervical CVS is more technically demanding than transabdominal CVS with more failures to obtain sample and more multiple insertions.

REVIEWER'S CONCLUSIONS

Second trimester amniocentesis is safer than transcervical CVS and early amniocentesis. If earlier diagnosis is required, transabdominal CVS is preferable to early amniocentesis or transcervical CVS. In circumstances where transabdominal CVS may be technically difficult the preferred options are transcervical CVS in the first trimester or second trimester amniocentesis.

Accuracy of abnormal karyotypes after the analysis of both short- and long-term culture of chorionic villi

We report in detail the cytogenetic results of 1838 consecutive chorionic villus samples with the availability of both short-term culture (STC-villi) and long-term culture (LTC-villi) preparations in 1561 cases (84.9%). A high degree of laboratory success (99.5%) and diagnostic accuracy (99.8%) was observed; in four cases of low mosaicism, all four associated with the final birth of a normal child, a small risk of uncertainty was accepted. The combined analysis of STC- and LTC-villi reduced follow-up amniocenteses by one-third in comparison with the analysis of STC-villi alone. We believe that the desired level of quality and accuracy of prenatal cytogenetics in chorionic villi can only be achieved when both STC- and LTC-villi are available. We conclude that CVS might then be the mode of prenatal diagnosis of first choice in pregnancies with a high (cytogenetic) risk.

Outcome of twin gestations after first trimester chorionic villus sampling

OBJECTIVE

To tabulate genetic results and obstetric outcomes of twin pregnancies after first-trimester chorionic villus sampling (CVS).

METHODS

The study included 262 consecutive women with twin pregnancies who had first-trimester CVS between 1988 and 1998.

RESULTS

Major indications for prenatal diagnosis included maternal age (n = 82), pregnancies after intracytoplasmic sperm injection (n = 114), or both (n = 33). Among 524 fetuses, 519 were sampled adequately. Cytogenetic results were incorrect because of sampling the same fetus twice in two pregnancies. In three pregnancies, contamination caused by mixed sampling made cytogenetic results uncertain. Correct genetic diagnoses were obtained in 509 fetuses, 24 of which had chromosomal abnormalities on direct preparations and four of which had monogenetic conditions. Additional invasive procedures were done on five occasions. Fifteen fetuses were terminated selectively. The total fetal loss rate was 5.5% (28 of 509). The indication for the procedure did not significantly determine the fetal loss rate. The mean +/- standard deviation (SD) gestational age at birth was 35.9 +/- 2.9 weeks, and the mean +/- SD birth weights for twins A and B were 2429 +/- 589.1 g and 2378 +/- 588.5 g, respectively.

CONCLUSION

First-trimester CVS is an accurate means of prenatal genetic diagnosis in twins, offering early selective termination in cases of abnormal genetic results in one of the fetuses.

Genetic analysis of fetal nucleated red blood cells from CVS washings

Chorionic villus sampling (CVS) is an established invasive prenatal diagnostic method for the detection of fetal chromosome aberrations. In 1-2% the karyotype result of CVS is inconclusive and follow-up confirmation will be required. To avoid another invasive procedure we examined fetal nucleated red blood cells (NRBCs) from CVS washings for genetic analysis. We analysed the washings of 20 chorionic villi samples of male fetuses. Fetal NRBCs were immunostained by an antibody against embryonic haemoglobin (HbE). FISH was performed with probes specific for the X and Y chromosome and the nucleus was counterstained with DAPI. Cells positive for the antibody, as well as for DAPI, were collected and stored by a semi-automated microscope. An operator reviewed those cells for their FISH signals. In 19 out of 20 CVS washings we found nucleated cells positive for HbE together with XY FISH signals. In none of the washings HbE positive cells with two X signals were found. Our results indicate that anti-HbE is a very specific antibody for identifying fetal NRBCs. NRBCs from CVS washings can be used as an additional fetal tissue for first trimester prenatal diagnosis.

First-trimester transcervical chorionic villus sampling by biopsy forceps versus mid-trimester amniocentesis: a randomized controlled trial project

Up to now, no data are available comparing amniocentesis and chorionic villus sampling (CVS) using biopsy forceps. A series of 1313 consecutive women referred to our unit before 12 weeks of pregnancy for fetal cytogenetic analysis because of advanced maternal age, were randomized into CVS with the use of transcervical biopsy forceps or mid-trimester amniocentesis. The diagnostic success rates of the two groups were 98 per cent and 100 per cent, and a second procedure was needed in 4.1 per cent (13/314) and in 0. 3 per cent (1/358), respectively. Follow-up was achieved in 98.7 per cent of the pregnancies. Postprocedure spontaneous fetal losses, until the first week after birth, in the 672 pregnancies that completed the trial accounted for 2.2 per cent (7/314) in the CVS group and 2.8 per cent (10/358) in the amniocentesis group. Although the trial was prematurely discontinued, and therefore the sample size was smaller than initially planned, the results indicate that transcervical CVS was as safe as mid-trimester amniocentesis.

When and how to assess fast-changing technologies: a comparative study of medical applications of four generic technologies

OBJECTIVES. To try to identify the optimal time at which to start assessing new and fast-evolving health technologies. To provide insight into factors influencing the timing of assessments and the choice of methods for assessing new and fast-changing technologies. HOW THE RESEARCH WAS CONDUCTED. A series of literature reviews were undertaken covering the general principles involved in the timing of health technology assessments (HTAs). Additionally, the reported assessments of laparoscopic cholecystectomy, chorionic villus sampling (CVS), teleradiology, teledermatology, genetic screening for predisposition to breast cancer, and gene therapy for cystic fibrosis were reviewed to try to identify the factors that influenced the timing of these assessments. Key individuals in each field were also interviewed. The selected technologies allowed comparison between those that were new and evolving and those that were relatively well-established. A bibliometric study of publication trends was also undertaken to see whether these trends would suggest points in the development of a technology that could be used as indicators that assessment should be started. RESEARCH FINDINGS. TIMING. The precise point at which assessment should start was not identified but the bibliometric study suggested that extending this approach might give useful results. For all health technologies, more regular reporting of outcomes and side-effects should be encouraged during the period after initial assessment and, where the technology is fast-changing, reassessment should take place from time to time. The precise intervals were not identified and the problem remains of deciding when a technology has changed enough to warrant reassessment. FACTORS INFLUENCING TIMING. Published reports of assessments did not generally specify the reasons for their timing, but a number of factors appear to have influenced the timing of those assessments, directly or indirectly. Product champions and opinion leaders pioneer the introduction of new technologies into clinical practice, and their reports may lead to the rapid diffusion of such technologies before they have been adequately evaluated, as was the case with laparoscopic cholecystectomy; this diffusion may limit the methods of evaluation that can then be used. It is therefore important to assess new health technologies before diffusion takes place. The extent to which regulatory control is imposed on the introduction of new health technologies can also influence the timing of assessments. Such controls might have helped to restrict the diffusion of laparoscopic cholecystectomy, making a large and widely generalisable randomised controlled trial (RCT) feasible. The source and availability of funding for studies may influence the nature and timing of trials. Many telemedicine evaluations were funded by commercial telecommunications organisations and were thus restricted in their timing (and biased towards the technological aspects of the applications) by the availability of funds. Media coverage undoubtedly has an influence although this influence is not always predictable; it may generate 'favourable' publicity about new health technologies, which can lead to immediate demands for the new technique, as was the case with laparosocpic cholecystectomy with its apparent benefits. Thus assessments should be made before media coverage exerts popular pressure on purchasers to adopt the technology and dissuades patients from participating in RCTs (because of fear they may be randomised to the standard treatment as occurred in a US trial of CVS). Innovators should also be cautious in the claims that they make to the media.(ABSTRACT TRUNCATED)

Accuracy of cytogenetic findings on chorionic villus sampling (CVS)--diagnostic consequences of CVS mosaicism and non-mosaic discrepancy in centres contributing to EUCROMIC 1986-1992

Of 62,865 karyotyped chorionic villus (CV) samples that were reported to EUCROMIC 1986-1992, 98.5 per cent showed either a normal karyotype (true negative result; 94.8 per cent of the total) or a non-mosaic chromosomal aberration (true positive non-mosaic result; 3.7 per cent). True fetal mosaicism was diagnosed in about 0.15 per cent of the 62,865 CV samples, while confined placental mosaicism (CPM) occurred in 1.0 per cent. False-positive non-mosaic aberrations were observed in 0.15 per cent and false-negative CVS (chorionic villus sampling) results in only 0.03 per cent. The remaining 0.15 per cent of the CVS results were unclassifiable. These figures determined a sensitivity of CVS for prenatal detection of chromosome aberrations of 98.9-99.6 per cent (95 per cent confidence intervals), a specificity of 98.5-98.8 per cent, a positive predictive value of 72.6-78.3 per cent, and a negative predictive value of 99.95-99.98 per cent. False-positive non-mosaic aberrations that could not from the outset be suspected of being confined to the placenta were very rare (0.07 per cent of CV samples). They most often involved non-mosaic monosomy X and trisomy 18 encountered after direct preparation alone. False-negative CVS results were extremely rare (0.03 per cent) and occurred, with only one exception, after direct preparation alone. Thirteen of the 19 false-negative CVS diagnoses were from pregnancies at a particularly high risk for fetal chromosomal aberration. Seventy-five per cent of the pregnancies with CVS mosaicism or non-mosaic discrepancy and known outcome continued to livebirth. When CVS mosaicism was encountered, the definitive prenatal cytogenetic diagnosis was most often obtained through subsequent amniocentesis. However, the use of amniocentesis and the frequency of pregnancy termination depended on the type of chromosomal aberration involved. We conclude that CVS is an accurate method for prenatal chromosome analysis. In pregnancies at high risk for fetal chromosomal abnormality, we recommend, however, not relying solely on a normal karyotype obtained after direct preparation alone.

Incidence and outcome of chromosomal mosaicism found at the time of chorionic villus sampling

OBJECTIVE

Chromosomal mosaicism has been reported in about 1% to 3% of chorionic villus sampling specimens. This report provides incidence and outcome information that should be useful in counseling patients found to have mosaicism on chorionic villus sampling.

STUDY DESIGN

A retrospective analysis of 11,200 consecutive patients undergoing chorionic villus sampling at the University of California, San Francisco, during the period from Jan. 1, 1984, to June 1, 1996, was undertaken.

RESULTS

A total of 140 cases of mosaicism were identified for an incidence of 1.3%. Follow-up information was available for 130 cases, 26 of which (20%) were confirmed in fetal tissue. Confirmation rates for specific types of mosaicism were as follows: autosomal trisomy 7.6%, sex chromosome 25%, structural abnormality 27.3%, and marker chromosome 77.8%. Neonatal outcome was normal in all cases for which pregnancy continued.

CONCLUSION

The data indicate that in most cases of chromosomal mosaicism found by chorionic villus sampling the mosaicism is unlikely to be clinically significant in the fetus.

Chorionic villus sampling and amniocentesis: recommendations for prenatal counseling. Centers for Disease Control and Prevention

Chorionic villus sampling (CVS) and amniocentesis are prenatal diagnostic procedures that are performed to detect fetal abnormalities. In 1991, concerns about the relative safety of these procedures arose after reports were published that described a possible association between CVS and birth defects in infants. Subsequent studies support the hypothesis that CVS can cause transverse limb deficiencies. Following CVS, rates of these defects, estimated to be 0.03%-0.10% (1/3,000-1/1,000), generally have been increased over background rates. Rates and severity of limb deficiencies are associated with the timing of CVS; most of the birth defects reported after procedures that were performed at > or = 70 days' gestation were limited to the fingers or toes. The risk for either digital or limb deficiency after CVS is only one of several important factors that must be considered in making complex and personal decisions about prenatal testing. For example, CVS is generally done earlier in pregnancy than amniocentesis and is particularly advantageous for detecting certain genetic conditions. Another important factor is the risk for miscarriage, which has been attributed to 0.5%-1.0% of CVS procedures and 0.25%-0.50% of amniocentesis procedures. Prospective parents considering the use of either CVS or amniocentesis should be counseled about the benefits and risks of these procedures. The counselor should also discuss both the mother's and father's risk(s) for transmitting genetic abnormalities to the fetus.

First trimester prenatal diagnosis: earlier is not necessarily better

In the past few years considerable attention has been given to a relatively new method of prenatal diagnosis known as chorionic villus sampling (CVS). Because CVS can be performed in the first trimester it is hailed by many as a significant advance over amniocentesis. What has not been as publicized, however, are the disadvantages of CVS and earlier prenatal diagnosis. The emotional costs of CVS in terms of the greater number of both spontaneous and selective abortions following CVS, the use of CVS for sex selection and, because of the greater social acceptability of first trimester abortion, the possibility of increased pressure on women to undergo prenatal diagnosis by health insurance companies, medical professionals and government agencies, all need to be weighed against the advantages of early prenatal diagnosis.

The predictive value of cytogenetic diagnosis after CVS based on 4860 cases with both direct and culture methods

Cytogenetic analysis was performed in 4860 chorionic villus samples by means of both direct preparation and long-term culture. The results of the analysis were compared with a classification including all theoretical types of combinations between the chromosomal constitution of the cytotrophoblast, extraembryonal mesoderm, and fetus, with the aim of evaluating the cytogenetic variability along the trophoblast-embryo axis. Eighteen of 29 possible combinations were found demonstrating a considerable heterogeneity. A mosaic conceptus was found in 1.5 per cent of cases, with generalized mosaicisms and confined mosaicisms in 0.2 and 1.3 per cent, respectively. Cytogenetic variability along the trophoblast-embryo axis was found in 1.42 per cent of cases. Results possibly leading to diagnostic errors (false-positive and false-negative results) were found in only 1.38 per cent. False-positive results of direct preparation were the most commonly observed discrepancy (0.8 per cent), while the incidence of false-positive results of the culture method and of both methods was 0.31 and 0.16 per cent respectively. The incidence of false-negative results was 0.1 per cent, with false-negative results of direct preparation 0.08 per cent and false-negative results of both methods 0.02 per cent. False-negative results of the culture method were not found. Our data confirm the high diagnostic accuracy of chorionic villus sampling and the utility of the combined use of the two methods in minimizing diagnostic errors and in reducing the need for follow-up amniocentesis.

A quantitative estimation of the effect of prenatal diagnosis in dizygotic twin pregnancies in women of advanced maternal age

Genetic counselling in a dizygotic twin pregnancy is complicated by the large number of possible pregnancy outcomes and by the conceivable differences in the parental valuation of these outcomes. We present the probability distributions of the pregnancy outcomes in dizygotic twin pregnancies for women from 35 to 45 years old without prenatal diagnosis and with transabdominal chorionic villus sampling (TA-CVS) or amniocentesis (AC), using data from the literature. TA-CVS always gives a higher probability of a favourable pregnancy outcome (the birth of one or two infants with a normal karyotype) than AC. For a 35-year-old woman, a 0.7 per cent risk of an unfavourable pregnancy outcome without prenatal diagnosis has to be weighed against the 2.1 per cent excess risk of loss of the entire pregnancy after TA-CVS. For a 45-year-old woman, a 10.2 per cent risk of an unfavourable pregnancy outcome without TA-CVS has to be balanced against a 4.4 per cent excess risk of pregnancy loss after TA-CVS. This study provides a quantitative tool for the support of individual parents with respect to the decision to undergo prenatal diagnosis in a dizygotic twin pregnancy.

Amniocentesis and chorionic villus sampling

Amniocentesis performed at 16 to 18 weeks' gestation has been the gold standard approach for prenatal cytogenetic diagnosis. Over the past few years, large collaborative studies on chorionic villus sampling have confirmed the safety and efficacy of chorionic villus sampling as a viable alternative for women seeking prenatal diagnosis. While the expanding experience with chorionic villus sampling has answered questions regarding the safety of the transabdominal approach, it has also raised questions concerning possible associations with limb abnormalities, its usefulness in multiple gestations, and the clinical significance of confined placental mosaicism. These issues, as well as the technical and gestational age limitations of chorionic villus sampling, have led many investigators to study the technical feasibility, safety, and accuracy of amniocentesis performed in the first trimester or early second trimester. While this approach appears both safe and efficacious, there are concerns regarding orthopedic abnormalities and the reliability of first-trimester amniotic fluid acetylcholinesterase and alpha-fetoprotein levels in the diagnosis of neural tube defects.

[Prenatal diagnosis of trisomy 21: limits of chorionic villi sampling]

An analysis of the limits, risks and difficulties of interpreting trophocentesis leads to the conclusion that the method is effective and free from maternal risk. The unsuccessful cases and the "fetal losses" are however more numerous than for amniocentesis.

Chorionic villus sampling in Auckland 1989-90

AIMS

to perform an audit of all 197 chorionic villus sampling procedures performed in Auckland in 1989-90.

METHOD

an attempt to trace the outcome in all 197 cases and this was possible in 188 cases.

RESULTS

89% of chorionic villus samples were performed transvaginally and 11% transabdominally. The total fetal loss rate was 9.6% (18) with six spontaneous miscarriages before 20 weeks gestation (3.2%), one intermediate fetal death and one neonatal death. There were 10 elective terminations of pregnancy following abnormal results so the spontaneous loss rate was 4.3%.

CONCLUSIONS

the loss rate was lower than that reported in the European and Canadian multicentre trials. The sampling success rate, however, was poor with 13.7% failed procedures. This improved in the second year of the service to 10%. There were no failure cultures or examples of mosaicism.

[Chorionic villi sampling and prenatal diagnosis]

The authors report their experience of 790 villous specimens taken either early (for 430 cases) or late (360 cases) between 10 and 37 weeks of amenorrhea (WA) using a transabdominal syringe. In the early choriocentesis cases, they conclude that use of the transabdominal route after 12.5 WA, regardless of the position of the chorion, makes it possible significantly to reduce the rate of fetal loss which becomes similar to that for amniocentesis. Placentocentesis has been used at later stages, either for high-risk couples as an alternative to amniocentesis (183 cases), or in cases of ultrasound abnormalities (177 cases) as an alternative to amniocentesis or cordocentesis. Placentocentesis makes it possible to obtain the fetal karyotype very rapidly within 1 to 2 days.

Fetal therapy

In the past year, the results of the European trial comparing chorionic villus sampling and amniocentesis have been published, supporting the findings of the Canadian Collaborative Study of an increased risk associated with chorionic villus sampling. The reporting of an increase in limb reduction abnormalities with chorionic villus sampling before 9 weeks has made us review our current practice. Other developments covered by this review include the management of mild cerebral ventriculomegaly, the treatment of tachyarrhythmias, and developments in fetal surgery. Throughout, the needs for continued collaboration, pooling of data, and the formation of international registers to extend the database from which both doctors and patients may benefit are highlighted.

[Cytogenic anomalies and placental function]

Over the past few years growing knowledge of placental cytogenetics has led to the surprising observation that the chromosomal constitution of the placenta is not always identical to that of its fetus. This information comes primarily from three sources: analyses of chorionic villi obtained by choriocentesis (chorionic villus sampling); studies of abortions, particularly spontaneous ones; and analyses of extrafetal tissues performed following dubious prenatal diagnoses, or to investigate fetal pathologies such as intrauterine growth retardation. Our personal data and those reviewed in this article allow the conclusion that chromosomal aberrations, particularly in the mosaic state, are frequent in the placenta, and that at least some of these have less severe consequences when present in extrafetal tissues than when present in the fetus itself. The types of chromosomal errors observed differ according to the method of ascertainment, in spontaneous abortions for example as compared to pregnancies developing as far as the third trimester. The presence of a partially aneuploid placenta may be compatible with a continuing pregnancy, but be associated with problems such as inadequate fetal growth.

[Experience with chorionic villi sampling]

The authors discuss their experiences from 412 chorion villus samplings, (CVS), which they have done under four and a half years since 1985. They used eight types of instruments in performing their examinations and each instrument proved to be satisfactory in the gaining of chorion villus samples, suitable for further tests. They also discuss the bacteria found most frequently in the vagina on the basis of the examination and culturing of both vaginal and cervical fluid done prior to 151 CVS examinations and the effective method with which ascending infection can be prevented. They discuss a distributional pattern of their results based on the different indications for the CVS examinations, and the outcome of each of the pregnancies after CVS. In 377 cases they did direct karyotyping, in 30 cases DNA examination and in five cases enzyme determination also occurred.

Medical Research Council European trial of chorion villus sampling. MRC working party on the evaluation pf chorion villus sampling

First-trimester chorion villus sampling has the advantage over second-trimester amniocentesis of allowing earlier prenatal diagnosis of various genetic and cytogenetic disorders in the fetus (and therefore earlier termination in affected pregnancies) but the relative safety and diagnostic accuracy remain unclear. Between 1985 and 1989, 3248 women seeking prenatal diagnosis, principally because of their age, were recruited to an international, multicentre, randomised comparison of the safety and diagnostic accuracy of the two techniques--5% of women allocated chorion villus sampling and 8% of those allocated amniocentesis were not tested, usually because of spontaneous miscarriage. 6% and 2% were retested, in most because of sampling failure. The endpoint of a liveborn infant who survived was achieved by 86% of women allocated chorion villus sampling and 91% of those allocated amniocentesis; statistical analysis, after appropriate weighting for a centre's contribution, showed that the typical difference between the groups was 4.6% (95% confidence interval 1.6-7.5%; p less than 0.01). This difference reflected more spontaneous fetal deaths before 28 weeks' gestation (2.9% [0.6-5.3%]); more terminations of pregnancy for chromosomal anomalies (1.0% [0.0-2.1%]); and more neonatal deaths (0.3% [-0.1 to 0.7%]). The difference in neonatal deaths was due to a preponderance of very immature liveborn infants in the chorion villus sampling group, and this factor also explained that group's longer mean stay in hospital. More abnormal diagnoses followed chorion villus than amniotic fluid analyses (5.6% vs 3.9%). This difference was largely due to diagnoses of trisomy 18 and of (usually mosaic) abnormalities known to be confined to the placenta. 3 terminated pregnancies were false positives, 1 tested by chorion villus sampling and 2 by amniocentesis, and 2 other mosaic cases diagnosed by chorion villus sampling may have been false positives. There was 1 false-negative result in the chorion villus sampling group. The possibility of earlier exclusion or diagnosis of some fetal disorders afforded by first-trimester chorion villus sampling must be set against its clinical risks.

Transabdominal chorionic villus sampling for rapid karyotyping in advanced gestation

Late pregnancy fetal karyotyping is not employed often because a clinical decision about labor and delivery may be required before the results would be available. However, percutaneous umbilical blood sampling (PUBS) has been used recently to obtain fast karyotypes. We have extended our chorionic villus sampling (CVS) procedure to the second and third trimesters and compared the results obtained with late CVS and PUBS. CVS karyotypes were obtained faster and may be technically easier to perform.

Randomized clinical trial of transabdominal versus transcervical chorionic villus sampling methods

The relative advantages and disadvantages of transabdominal (TA) and transcervical (TC) chorionic villus sampling (CVS) in terms of fetal risks and efficacy were evaluated in a clinical trial conducted on 1194 women randomized at 7-12 weeks' gestation. The results of the study indicate that, if any, the relative risk of fetal loss following either procedure is less than double that of the alternative technique when performed by a skilled operator. Overall, the fetal loss rate (spontaneous abortions following randomization, terminations of pregnancy, and perinatal deaths) is 16.5 and 15.5 per cent, respectively, among women allocated to TA- and TC-CVS. The two procedures are equally effective, although TA-CVS is associated with a significantly lower rate of repeat device insertions; on the other hand, a higher weight of chorionic tissue is obtained, on average, with TC-CVS. Bleeding is more common following TC-CVS, while peritoneal reaction developed only after TA-CVS. No diagnostic problems specifically related to one sampling technique were identified.

Chromosome analysis guidelines preliminary report

These guidelines have been developed by the Association of Cytogenetic Technologists (ACT) for chromosome analysis. In formulating its recommendations, the task force reviewed guidelines established by several states and regional genetics groups. Draft guidelines prepared by the task force were reviewed by a panel of expert consultants, all of whom are laboratory directors and well known in their respective fields of expertise. The intention of the task force was to reflect procedures that are believed to be generally accepted by cytogenetic laboratories as basic criteria for effective chromosome analysis and that are consistent with existing cytogenetic quality assurance guidelines. It is important to stress that the primary purpose of the task force at this time is to establish guidelines for chromosome analysis. While the present guidelines address issues other than chromosome analysis, they do so incidentally and only in general terms. A more comprehensive discussion of other technical aspects of cytogenetics can be found in the forthcoming second edition of the ACT Cytogenetics Laboratory Manual. It is important to note that these guidelines are not intended to prescribe appropriate analyses for all individual circumstances. That determination is appropriately a matter for the judgment of the laboratories concerned. ACT, its members, and the task force that assisted in preparation of these guidelines make no warranty and assume no liability with respect to the information contained herein.