Evaluation of transcervical chorionic villus sampling with a completed follow-up of 1550 consecutive pregnancies

Clinical proceduress in prenatal diagnosis

The prenatal diagnosis of fetal genetic disease has become a routine part of obstetric care. Pregnancies at risk are identified by a number of factors, including maternal age, positive serum screening, a history of a previous affected child, a parental chromosome rearrangement or an ultrasound-identified anomaly. Invasive diagnostic testing can be performed in the first trimester by chorionic villus sampling or in the second trimester by amniocentesis. Both procedures are safe, with an equivalent 0.5% risk of procedure-induced pregnancy loss. When performed prior to the routine sampling window of 15 weeks, amniocentesis may increase the risk of talipes equinovarus, the highest risk being encountered prior to 13 weeks' gestation. When chorionic villus sampling is performed prior to 9 weeks' gestation, there may be an increased risk of limb reduction defects. The laboratory analysis of both procedures is reliable. Chorionic villus sampling has a 1-2% incidence of confined placental mosaicism, requiring additional evaluation in some cases.

Chorionic villus sampling

Chorionic villus sampling (CVS) has been used a successful and safe first-trimester prenatal diagnostic technique for over 12 years. Developed to avoid the medical and psychological complications of later prenatal diagnosis by amniocentesis, CVS rapidly has become a primary tool for the diagnosis of fetal cytogenetic, molecular, and biochemical disorders. In addition, its development has led to an improved understanding of several biological processes, including confined placental mosaicism and uniparental disomy.

Chorionic villus sampling by biopsy forceps. Results of 1580 procedures from a single centre

The results of a prospective series of 1580 chorionic villus sampling (CVS) procedures using biopsy forceps are presented. Most of the procedures (1442), including 11 sets of twins, were performed by the transcervical approach (TC-CVS), using a curved-shank thin forceps, and 138 by the transabdominal approach (TA-CVS), using a trocar-guided straight thin forceps. The mean gestational age for TC-CVS was 10.9 weeks, and in 233 cases (16 per cent) the procedure was carried out between the 12th and 14th weeks. The mean gestational age for TA-CVS was 16.7 weeks. The major indication for CVS was advanced maternal age (92.7 per cent in the TC and 91.8 per cent in the TA approach), and indications for abnormal ultrasound findings were more common in the TA approach (4.5 per cent) than in TC-CVS (0.07 per cent). Although sampling was apparently accomplished in all the procedures, in 3.1 per cent of the TC-CVS and 2.2 per cent of TA-CVS procedures, the samples were less than 1 mg after dissection. A cytogenic report was obtained in 96.1 per cent of the TC-CVS and 90.6 per cent of the TA-CVS. Maternal serum alpha-fetoprotein (MSAFP) was measured before and after TC-CVS and the post-CVS MSAFP was positively correlated with the sample weight. Second-trimester amniocentesis following CVS was required in 5.2 per cent (TC-CVS) and 6.5 per cent (TA-CVS), due to the failure to obtain a cytogenetic report or diagnostic confirmation. The follow-up to the 20th week was 100 per cent by ultrasound scan, and 88.6 per cent from the 21st week to 1 week after delivery. Fetal loss rates within 2 weeks of the procedure were 1.7 per cent (TC-CVS) and 0.8 per cent (TA-CVS) and total fetal loss accumulated to 1 week after delivery was 4.6 per cent (TC-CVS) and 5.9 per cent (TA-CVS). Factors found to increase significantly fetal loss in the TC-CVS series were maternal age and the collection of very small samples, but not the number of forceps insertions.

Experience with 1251 transcervical chorionic villus samplings performed in the first trimester by a single team of operators

OBJECTIVE

We report our experience with 1251 chorionic villus samplings (CVS) performed by a single team of operators.

STUDY DESIGN

From April 1984 through August 1993, 1251 CVS were performed in 1236 pregnancies. The transcervical route was used in the vast majority and the sampling was performed during the 9th through 13th weeks of gestation in 1193 cases (96%). Follow-up was ensured to tabulate the pregnancy-related complications and fetal loss rate until 28 weeks' gestation. Pregnancy outcome was documented for all but 36 women (3%).

RESULTS

Most of the tests (72%-891/1236 pregnancies) were performed for advanced maternal age (> or = 35 years). The percentage of each indication remained relatively stable, around 90% for chromosomal indications and between 8 and 11% for DNA studies. Samples adequate for diagnosis were obtained in one or two sessions in 1179 pregnancies (95%). The rate of spontaneous abortion possibly related to CVS was 2.5% (28/1092). Mosaicism confined to the placenta was found in 23 cases (1.8%). The pregnancy outcome was known in 1098 pregnancies. There were 10 perinatal losses (0.9%) and nine congenital malformations (0.8%). No transverse limb defects were observed. The rate of premature deliveries (4.6%) and of small for gestational age were comparable to the general uninstrumented population.

CONCLUSION

CVS is a safe and effective mode of antenatal diagnosis when performed by a single team of experienced operators.

Retrospective study of trisomy 18 in chorionic villi with fluorescent in situ hybridization on archival direct preparations

Trisomy 18 in direct chorionic villus preparations needs further investigation since the chromosome abnormality may be confined to the placenta and may not represent the actual fetal karyotype. We performed, retrospectively, fluorescent in situ hybridization (FISH) with the chromosome 18 centromere probe (L1.84) on interphase nuclei of destained slides of all cases of full trisomy 18 (n = 22) and mosaic trisomy 18 (n = 8) detected among 7600 first-trimester chorionic villus samples during an 8-year period (1985-1992). More nuclei displaying three signals were encountered in cases of full and mosaic trisomy 18 confirmed in fetal tissue than in non-confirmed cases. FISH can be useful for the verification of trisomy 18 in direct chorionic villus preparations.

Testing for fetal abnormality in routine antenatal care

The detection of fetal abnormality is a major component of routine antenatal care. A variety of techniques are now in use, although these are constantly being modified in the pursuit of more accurate and earlier detection. In this paper we draw attention to the distinction between screening and diagnostic tests, and describe the techniques which have been most commonly used in the UK: serum-screening for neural tube defects; screening for Down's syndrome; ultrasound scanning; amniocentesis and chorionic villus sampling.

Terminal transverse limb defects and early chorionic villus sampling: evaluation of 4,300 cases with completed follow-up

Data from 4,300 consecutive cases following prenatal diagnosis by transcervical (TC) CVS (n = 1,570) and transabdominal (TA) CVS (n = 2,370) were evaluated. In the follow-up study only infants examined by a physician were included. Gestational age varied between 8.5 and 11.6 weeks (mean 10.3 weeks) for TC-CVS and between 9.3 and 20 weeks (mean 12.3 weeks) for TA-CVS 98% of TC-CVS was performed at 9-10 weeks, 80.7% of TA-CVS procedures were carried out at 12-15 weeks. Selective termination took place in 97 cases of TC-CVS (6.1%) and in 72 cases of TA-CVS (2.6%). Another 8 women had a termination for psychosocial reasons, resulting in 4,123 (1,469 TC, 2,654 TA) continuing pregnancies. The overall fetal loss rate < 28 weeks was 5.4% (n = 80) for TC-CVS and 2.6% (n = 70) for TA-CVS. The overall incidence of congenital abnormalities after birth was 0.9%. Two terminal transversal limb defects were detected in the TC-CVS group (0.14%) against one (0.04%) in the TA-CVS group.

Chorionic villus sampling: quality control--a continuous improvement model

OBJECTIVE

Our purpose was to describe Vanderbilt University Medical Center's experience in establishing a chorionic villus sampling program and the importance of quality control along with a continuous improvement model on the first 1000 cases.

STUDY DESIGN

A continuous improvement model was established with emphasis on a multidisciplinary team approach and quality assurance process. A computerized data base was used for continuing analysis of complications and for allowing facile access to pertinent information.

RESULTS

A continuous improvement model allowed for an improved process and outcome for patients, personnel, and referring health care providers. Follow-up for initial symptoms after chorionic villus sampling was obtained on 98.5% of patients. Pregnancy follow-up, including birth data, was obtained on 93%.

CONCLUSION

A continuous improvement mode from the project's onset resulted in an improved process and outcome, information helpful for accessing spontaneous abortion rates and pregnancy outcomes (including the incidence of limb abnormalities and factors associated with abortions) and recommendations for training personnel.

Importance of complete follow-up of spontaneous fetal loss after amniocentesis and chorion villus sampling

Women who are the most difficult to trace after amniocentesis or chorion villus sampling are often those who have had an adverse pregnancy outcome. To calculate total fetal loss figures for use in prenatal counselling we have followed in a multicentre study 100% of women who had undergone these procedures. Early spontaneous loss (within three weeks of the procedure) and total spontaneous loss were much lower after amniocentesis (0.2% and 1.3%, respectively) than after chorion villus sampling (1.2% and 2.9%). Four spontaneous fetal losses among the 20 pregnancies that were the most difficult to follow-up increased the loss rate by 0.5% for chorion villus sampling. Risk of early fetal loss after chorion villus sampling was related to experience of the operator (relative risk [RR] 4.3, p = 0.003), and total fetal loss was lower in pregnancies tested at 10 weeks' or more gestational age compared with those tested before 10 weeks' (RR 0.4, p = 0.01). A table showing the frequency of each of the seven possible outcomes after amniocentesis and chorion villus sampling is useful in counselling those considering one or other test.

Chorionic villus sampling: evaluation of obstetric performance

Chorionic villus sampling is frequently utilised in the Nottingham region as a means of early prenatal diagnosis of genetic problems. Its relative safety in the early antenatal period is well established but there has been some concern that perinatal mortality may be greater in the chorionic villus sampling group as compared to amniocentesis. We have in response studied our own data and report the obstetric outcome in 144 cases where the pregnancy has progressed beyond 28 weeks gestation. We have selected a procedure free control group matched for parity. We have found no significant difference in the perinatal outcome and obstetric performance and conclude that at this juncture we should continue to offer our services as chorionic villus sampling offers significant advantages in the first trimester over amniocentesis.

The contribution of DNA analysis to carrier detection and prenatal diagnosis of hemophilia A and B

Developments in DNA technology have provided a novel means of carrier detection and prenatal diagnosis of hemophilia A and B. The collection of a large set of data has enabled us to evaluate the present feasibility and reliability of a diagnosis at the gene level and its contribution to methods already available. Since 1984, 533 potential and obligate carriers belonging to 170 families with hemophilia have been referred to us. By the combined use of pedigree analysis, coagulation assays, and DNA (RFLP) analysis, certainty about the carrier status has been markedly increased for the potential carriers. Although RFLP analysis revealed the possible origin of the mutation in many families with an isolated patient, uncertainty remained for quite a number of their female relatives because of the possible occurrence of germline mosaicism. Forty-one women requested prenatal diagnosis during one or more pregnancies. The short time interval between pregnancies, even after abortion of an affected fetus, proved that first-trimester prenatal diagnosis has become an acceptable option for women at risk. Recently, efficient methods for direct identification of mutations have been developed, and they may allow a definite diagnosis for all families with hemophilia in the near future.

Acceptance of chorionic villus sampling in the southwest region of The Netherlands: a 5-year evaluation

The acceptance of chorionic villus sampling (CVS) for monitoring pregnancies at risk for chromosomal and genetic disorders was studied from its introduction in the Centre for Clinical Genetics in Rotterdam in 1984 until 1988. Special attention was given to increasing acceptance in the group with advanced maternal age (AMA) (12.6% CVS in 1984, 52.2% CVS in 1988) and the group with a high genetic risk (HGR) (42.7% in 1984, 86.7% in 1988). The odds-growth-rate in CVS was 1.64 and 1.67 respectively, which was not significantly different. The relatively limited use of CVS at AMA is most likely determined by the fact that a considerable number of patients are referred too late in pregnancy to have the option of CVS.

Chorionic villus sampling: analysis of fetal losses to delivery, placental pathology, and cervical microbiology

A population of 1639 patients were seen for chorionic villus sampling (CVS). Embryonic death was identified at ultrasound in 5.3 per cent of patients. The number of patients undergoing CVS was 1551, with 1416 transcervical procedures and 135 transabdominal procedures. The most common indication for CVS was advanced maternal age. Spontaneous pregnancy losses identified by increased risk of pregnancy loss with increasing aspiration attempts. The total fetal loss for this population was 5.4 per cent with the pregnancy loss estimated due to procedure being 1.2 per cent. Analysis of placentae from patients having CVS and amniocentesis showed no differences. Microbiological assessment prior to CVS was similar to previous publications.

Transcervical (TC) and transabdominal (TA) CVS for prenatal diagnosis in Rotterdam: experience with 3611 cases

Data from 3611 consecutive CVS (TC, N = 1780; TA, N = 1831) were analysed with emphasis put on influence of maternal and gestational age at CVS on the fetal loss rate less than 28 weeks. For TC-CVS the gestational age varied from 9.3-11.6 weeks, for TA-CVS from 9.3-20 weeks. Sampling efficacy at first attempt was 86.5 per cent and 95 per cent respectively. In 4.6 per cent an abnormal result was established. In older mothers (N = 2362) the fetal loss rate was significantly higher (p = less than 0.05) when sampled before 12 weeks (TC-CVS 6.2 per cent, TA-CVS 5.8 per cent). When the CVS (TA) was performed after 12 weeks the fetal loss rate decreased to 2.4 per cent. In 1079 younger women the fetal loss rate remained low (TC 2.8 per cent; TA less than 12 weeks 1.8 per cent; TA greater than 12 weeks 1.7 per cent) and was not influenced by gestational age at the time of sampling. We concluded both methods safe and reliable when the choice of application considers maternal age.

The safety of chorionic villus sampling. A synthesis of the literature

Altogether 10 reports on the safety of chorionic villus sampling, either by the transcervical (TC) or the transabdominal (TA) approach, were reviewed and combined with our own data. After discussion of how unintended fetal loss rates are best estimated, the excess total fetal loss after TC and TA compared with amniocentesis were estimated to be 1.70% (+/- 0.65%) and practically zero (+/- 1.0%), respectively (standard errors in parentheses). The absolute risk of unintended loss after TC is +2.7% (+/- 0.7%) and after TA 1.0% (+/- 1.0%). These estimates are still too uncertain to allow precise weighting of benefits and human costs. A uniform style of reporting studies in this area is proposed.

Transabdominal chorion villus sampling: a safe and reliable procedure

A complete follow-up of the first 578 patients undergoing transabdominal chorion villus sampling (TACVS) in our combined practices was undertaken to determine the pregnancy loss rate. Factors contributing to losses and the problems incurred in achieving a clinically relevant result were also examined. It was found that increasing experience led to fewer procedural difficulties but that there persisted a higher problem rate in those women with a retroverted uterus. In 98.1% of patients an adequate volume of tissue was obtained and in 95.5% a clinically relevant result was achieved. This second figure rose to 96.3% in the latter part of the study. There was a total fetal loss rate of 2%, with only 0.5% (3 patients) having a missed abortion within 4 weeks of the procedure. It is concluded that TACVS is a reliable procedure with a high level of safety.

Interpretation of chromosome mosaicism and discrepancies in chorionic villi studies

In 3,000 chorionic villi studies (CVS) 33 cases of mosaicism and 7 false-positive cell lines in all cells were seen. The mosaic cell lines were caused by aneuploidy of autosomes (13x), sex chromosomes (9x), and structural anomalies (11x). Mosaics of fetal origin were only 4 cases of trisomy 21 and one 47,XXY mosaic. In 7 cases abnormal karyotype of non-fetal origin was seen in all cells in direct studies, including trisomy 16 (3x) and trisomy 18 (2x). The combined use of direct CVS and cell cultures always uncovered the non-fetal origin of chromosome abnormalities and the study of cultured cells in all cases could have prevented 5 terminations. Complete follow-up studies demonstrated no false-negative results. Therefore, CVS can be nearly 100% accurate when both direct studies and cultures are examined in cases of mosaicism and other cell lines of possible non-fetal origin, such as trisomy 16, trisomy 18, translocation (21;21), and 45,X cells.

Direct chromosome preparation and culture using chorionic villi: an evaluation of the two techniques

We present a comparison between direct chromosome preparation and cell culture for first trimester fetal chromosome study using chorionic villi. The 2 techniques have advantages and disadvantages and are demonstrated to be appropriate for routine diagnostic work. The combined use of both methods may optimize the quality of the chromosome study and minimize the possibility of false-positive and false-negative findings.