Chorionic villus sampling. Evaluating safety and efficacy

Uptake of noninvasive prenatal testing at a large academic referral center

OBJECTIVE

Noninvasive prenatal testing (NIPT) is a recently developed risk-assessment technique with high sensitivity and specificity for fetal aneuploidy. The effect NIPT has had on traditional screening and diagnostic testing has not been clearly demonstrated. In this study, NIPT uptake and subsequent changes in the utilization of first-trimester screen (FTS), chorionic villus sampling (CVS), and amniocentesis in a single referral center is reported.

STUDY DESIGN

Monthly numbers of NIPT (in high-risk patients), FTS, CVS, and amniocentesis were compared between a 35-month baseline period (April 2009 through February 2012) before introduction of NIPT, and the initial 16 months following NIPT introduction divided in 4-month quarters beginning in March 2012 through June 2013.

RESULTS

A total of 1265 NIPT, 6637 FTS, 251 CVS, and 1134 amniocentesis were recorded over the 51-month study period in singleton pregnancies of women who desired prenatal screening and diagnostic testing. NIPT became the predominant FTS method by the second quarter following its introduction, increasing by 55.0% over the course of the study period. Total first-trimester risk assessments (NIPT+FTS) were not statistically different following NIPT (P = .312), but average monthly FTS procedures significantly decreased following NIPT introduction, decreasing by 48.7% over the course of the study period. Average monthly CVS and amniocentesis procedures significantly decreased following NIPT introduction, representing a 77.2% and 52.5% decrease in testing, respectively. Screening and testing per 100 morphological ultrasounds followed a similar trend.

CONCLUSION

NIPT was quickly adopted by our high-risk patient population, and significantly decreased alternate prenatal screening and diagnostic testing in a short period of time.

Genetic testing: predictive value of genotyping for diagnosis and management of disease

This article describes predictive, preventive value of genetic tests and the implication of the use of testing for personalized treatment. This year marks the 10th anniversity of publishing of the sequence of the human genome. One important area of application of this mega project is a development of genetic tests for mutation detection in single gene disorders that has impact for pediatric age group patients and analyzing susceptibility genes as risk factors in common disorders. Types of genetic tests, new emerging technologies will enable developments of high-throughput approaches by microarrays of great application capacity as described here. As it is usual for all technologies used in health care, bioethical concerns has to be delt with. The ethical, social and governance issues associated with genetic testing are discussed.

Is routine AFP screening in pregnancy reassuring?

The purpose of the study is to examine the impact of a negative result on a routine prenatal screening test, maternal serum alpha-fetoprotein screening for spina bifida and Down's syndrome. Three-hundred and nine women had the test and 30 did not. Twenty-one of the 309 did not think that they had been tested, and seven women who did not have the test thought that they had been tested. There were no significant differences between these four groups in anxiety, certainty about the baby's health or worry about the baby's health. These results suggest that the receipt of a negative result on this screening test does not provide reassurance. There are several possible explanations for this finding: the test is reassuring, but only for a small number of those undergoing the test; the test is reassuring but the study method was inappropriate and hence failed to detect it; the test is not reassuring because of a lack of knowledge about the meaning of a negative result or, the way in which results of testing are conveyed. The latter two explanations suggest that the potentially reassuring effects of such a result may be realised with more effective communication about test results.

Prenatal diagnosis of beta thalassaemia based on restriction endonuclease analysis of amplified fetal DNA

In the Mediterranean area, 50% of the beta thalassaemia mutations abolish or create a restriction endonuclease site in the beta globin gene. This study describes a new procedure for prenatal detection of these beta thalassaemia defects based on the direct visualisation, on an ethidium bromide stained polyacrylamide gel, of the discrete DNA fragments produced by restriction endonuclease digestion of fetal DNA, enzymatically amplified using the DNA polymerase from the thermophilus bacterium Thermus aquaticus. We applied this procedure to the Sardinian population to detect the nonsense mutation at codon 39 and the frameshift at codon 6 of the beta globin gene; these are the most frequent beta thalassaemia mutations in this population, accounting for 95% and 2.2% of the beta thalassaemia chromosomes. The main advantages of this procedure are simplicity (no radioactivity), sensitivity (0.2 microgram of DNA), and rapidity (12 hours). The very small amount of fetal material required makes amniotic fluid cell culture unnecessary and may decrease the fetal loss rate associated with trophoblast sampling. By circumventing the use of radioactive and non-radioactive probes, the spread of this technology to the high risk areas will be facilitated.

Spontaneous and induced chromosome breakage in chorionic villus samples: a cytogenetic approach to first trimester prenatal diagnosis of ataxia telangiectasia syndrome

Patients with ataxia telangiectasia (AT) syndrome exhibit a high level of spontaneous chromosome aberrations, with hypersensitivity to gamma radiation and radiomimetic chemicals at the chromosomal and cellular level. Previously pregnancies at risk for AT have been screened solely by analysis of amniotic fluid samples. In this report we describe a cytogenetic approach to the prenatal diagnosis of AT using chorionic villus sampling (CVS). Levels of spontaneous and induced (gamma radiation and bleomycin) chromosome breakage were established in direct, semidirect, and culture preparations of CVS samples from normal pregnancies. The methods developed were then successfully applied to the screening of a pregnancy at risk for AT. Semidirect preparations showed normal levels of chromosome breakage, and this result was further confirmed in chorion, amniotic fluid, and lymphocyte cultures. In chorion villus samples, gamma radiation is probably the easiest and most reliable way of discriminating between unaffected fetuses and those with AT.

Investigations of chorionic villi after chorionic villus sampling (CVS). Correlation of morphological with clinical and laboratory data

This report documents the first 262 cases of chorionic villus sampling (CVS) performed in parallel with cytogenetic and morphological investigations. Histomorphological examination of these CVS specimens gave suitable results in about 96% (251 cases). Of the latter, 201 samples (80.1%) exhibited villi and 176 (70.1%), maternal tissue. Viability and maturation of the chorionic villi were determined light microscopically even in cases with few villus trees. Smooth avascular villi with poorly defined margins observed under an inverted microscope, less than 10 mitoses after short-term incubation, and reduced growth of cell cultures were significantly correlated with sampling at the chorion laeve by means of histomorphologic criteria. Villi from cases exhibiting cytogenetically proved chromosomal abnormalities were characterized by molar degeneration or stromal fibrosis, or both, in 4 out of 9 cases, including 3 mosaics. In early abortions (within 3 weeks after CVS), an unexpectedly high rate of pathohistological changes within maternal tissue was evident. These results need further confirmation by investigation of a greater number of samples with immunohistochemical and morphometric methods.

The impact of prenatal screening and diagnostic testing upon the cognitions, emotions and behaviour of pregnant women

The purpose of most screening and diagnostic tests is to initiate treatment when a problem is found and, otherwise, to allay anxiety. The extent to which the second of these objectives is met was studied in a prospective study of 179 pregnant women. Women who had amniocentesis to detect Down's Syndrome or were screened for a fetal neural tube defect had significantly lower anxiety levels in the third trimester of pregnancy than women who did not undergo these tests. Undergoing screening for a neural tube defect was also associated with a more positive attitude towards the pregnancy in the second trimester. These results suggest that the previously reported raised levels of anxiety in women undergoing such tests do not necessarily remain high for the duration of the pregnancy and, indeed, undergoing testing may serve to protect women against high levels of anxiety in the third trimester of pregnancy.

Chromosome banding in direct preparations of chorionic villi

Chorionic villus sampling (CVS) is now currently offered for first trimester prenatal diagnosis of genetic disorders. Chromosome analysis of CVS in direct and culture preparations is possible using modifications of standard banding techniques. We summarize our experience in applying QFQ, GTG, RBG, CBG, DA/DAPI, NOR, and SC differentiation protocols to direct preparations. Characteristic chromosome regions are properly labelled by these techniques, and analysis of 300 band stage karyotypes is consistently achievable on GTG banded direct preparations. However, banding of CVS direct chromosomes has proved to be difficult, and the analysis needs to be backed up by culture preparations.

Chorionic villi sampling: a nursing perspective

A relatively new procedure, chorionic villi sampling is now available as an alternative method for prenatal diagnoses of genetic disorders during pregnancy. Indications, procedures, risks, advantages, and nursing implications of this procedure are defined and described. Readers are thereby provided with current information concerning prenatal genetic diagnosis that may be passed on to patients in need of this information.

Importance of databases for technology assessment

The data indispensable for carrying out the comprehensive, multi-faceted process of medical technology assessment (MTA) should be collected from a variety of sources. The authors distinguish between type "A" general data, useful for assessment but collected without this specific aim, and type "B" data. Registries of health care procedures or of diseases, as well as clinical data bases are quoted as examples of type "B" data, specifically relating to MTA. Since demographic methods are of importance for the evaluation of long-term effects of medical technologies, examples of sources of type "A" data are presented. Their significance for health policy making is discussed.

Data bases for the assessment of medical technologies. Examples from Europe

The assessment of medical technologies has to answer several questions ranging from safety and effectiveness to complex economical, social, and health policy issues. The type of data needed to carry out such evaluation depends on the specific questions to be answered, as well as on the stage of development of a technology. Basically two types of data may be distinguished: (a) general demographic, administrative, or financial data which has been collected not specifically for technology assessment; (b) the data collected with respect either to a specific technology or to a disease or medical problem. On the basis of a pilot inquiry in Europe and bibliographic research, the following categories of type (b) data bases have been identified: registries, clinical data bases, banks of factual and bibliographic knowledge, and expert systems. Examples of each category are discussed briefly. The following aims for further research and practical goals are proposed: criteria for the minimal data set required, improvement to the registries and clinical data banks, and development of an international clearinghouse to enhance information diffusion on both existing data bases and available reports on medical technology assessments.

Difficulties encountered in a randomization trial of CVS versus amniocentesis for prenatal diagnosis

In April 1985, having completed a study of the short-term complications of chorionic villus sampling (CVS), we began a randomized comparison of CVS versus amniocentesis. Our study continued over a 15-month period, and during that time we had difficulty recruiting patients, with only 10.6% of 1254 women referred for prenatal diagnosis fully participating in this study. However, 30.2% of those eligible by dates and indication chose to enter the study. CVS was available in our province only through this study, and the two most common reasons for such a low rate of recruitment were reporting too late in pregnancy and the concern about the potential risks of CVS. Patients continued to seek counselling too late for CVS despite direct and continuous contact with regional physicians. Our patients' concern about risk might well vary with the attitude of their physicians towards CVS, and with the information provided at the time of pre-test counselling. The small number of patients actually enrolled did not permit any meaningful comparison of amniocentesis to CVS. However, our experience with pregnancies lost post-CVS suggests that a pregnancy with an apparent low implantation at the time of sampling may be at a higher risk of loss.

Risks of chorion villus sampling

From the experience accumulated in less than 4 years of chorionic villus sampling activity, much has been learned about the advantages of prenatal diagnosis in the first trimester. The safety of the procedure during this developmental stage has been extremely good. The record in this centre with over 2700 cases sampled and over 2000 deliveries has demonstrated a fetal loss rate similar to that observed in amniocentesis studies. It appears that fetal loss that may be attributed to the procedure is not more than 1% and may be less. Some of that loss appears to be correlated with avoidable trauma to the chorionic membrane area. If this conclusion is valid, then avoidance of this pattern even in the occasional difficult case may further improve the already acceptable safety record of the procedure.

Chorionic villus sampling by rigid forceps: experience with 300 cases at risk for thalassemia major

In this article we report the results of chorionic villus sampling by a biopsy forceps inserted via the cervix under ultrasonic guidance in 300 pregnancies at risk for thalassemia major. A sufficient amount of chorionic villi for deoxyribonucleic acid analysis by oligonucleotide hybridization was obtained in all cases tested but one, with a success rate of 99.7%. The percentage of fetal loss, expressed as proportion of continuing pregnancies, was 4.8%. To verify the results, we carried out amniocyte deoxyribonucleic acid analysis in all the continuing pregnancies for the first 100 cases and in those in which trophoblast deoxyribonucleic acid analysis showed the heterozygous state for beta-thalassemia for the second 200 cases. At the beginning we had two cases of decidual contamination in such an amount to cause misdiagnosis. Successively more careful elimination of decidual tissue from villi avoided avoided this pitfall. These results indicate that chorionic villus sampling by a rigid forceps is a reliable and relatively safe method for fetal diagnosis of genetic diseases by deoxyribonucleic acid analysis.

Fetal blood group determination in first-trimester pregnancy for the management of severe immunization

The presence or absence of Rho (D) and Kell antigens on fetal red blood cells was determined in the first trimester of pregnancy on erythrocytes obtained by chorionic villi sampling with the use of mixed agglutination and solid phase microimmunofluorescence techniques. Pregnancies in one Kell-sensitized woman and seven severely RH-sensitized women with a poor obstetric history and a partner heterozygous for the offending antigen were examined. A conclusive diagnosis could be made in seven of the eight cases studied.

Chromosomal mosaicism of trisomy 7 restricted to chorionic villi

Chromosomal mosaicism confined to the placenta is a serious problem in first-trimester fetal diagnosis. We report a case of mosaicism of trisomy 7. The aneuploid cell line could not be confirmed in fetal tissue.

Effect of chorionic villus sampling and early pregnancy counselling on uptake of prenatal diagnosis

An early pregnancy counselling clinic was introduced to improve the uptake of prenatal diagnosis and to offer chorionic villus sampling to women aged 38 and over by their expected date of delivery. Ninety eight (62%) unselected older mothers were seen before 11 weeks' gestation, and 23 (32%) of those with viable pregnancies elected to undergo chorionic villus sampling compared with 38 (52%) electing amniocentesis. A quarter of the patients booking before 11 weeks had a miscarriage. Because of the future potential demand for chorionic villus sampling counselling during pregnancy and referral of eligible patients should occur as early as possible.

Clinical applications of gene probes in human genetic disease, malignancy, and infectious disease

Recent developments in recombinant DNA technology have made possible the production of gene probes consisting of cloned gene segments, cloned segments of DNA linked to genes, and synthetic gene fragments. Several methods have been developed by which these probes may be used for the diagnosis of human disease. This technology has been outstandingly successful for prenatal diagnosis and carrier detection in many genetic diseases. These methods have also been successfully applied to the analysis of human malignancies, by providing for the determination of cell lineage and clonality in lymphoid neoplasms. Finally, these methods have shown potential for rapid and sensitive diagnosis of some infectious diseases.

Transabdominal chorionic villus sampling

Transabdominal chorionic villus sampling, carried out with a fine-bore needle and cannula under ultrasound guidance, was as successful as transcervical aspiration but avoided the risks of bacterial contamination associated with the latter technique. The transabdominal procedure can be carried out under local anaesthesia, and multiple samples can be obtained, if necessary, through a single cannula.

First trimester diagnosis of beta-thalassaemia in a twin pregnancy

This paper reports the results of first trimester prenatal diagnosis in a twin pregnancy at risk for homozygous beta 0-thalassaemia (beta 0-39 mutant). Trophoblast samples from both twins were obtained at 10 weeks gestation with a forceps guided by ultrasound. Trophoblast DNA analysis, carried out with the oligonucleotide technique, revealed that one fetus was homozygous and the other heterozygous for the beta-39 mutant. This diagnosis was confirmed at 17 weeks gestation by amniocyte DNA analysis. DNA polymorphism analysis within the alpha-globin gene provided useful genetic markers for twin differentiation.