A survey of current clinical practice of chorionic villus sampling.

OBJECTIVE: The number of invasive procedures (chorionic villus sampling (CVS) or amniocentesis) for fetal testing is decreasing because of the availability of non-invasive prenatal test (NIPT) leading to a centralisation of prenatal diagnostic services to accredited fetal medicine centres. A new survey was conducted 10 years after the previous one to update the current clinical practice among clinicians who regularly perform CVS. METHOD: Consultants from 32 centres in the United Kingdom were invited to take part in an online survey evaluating: The total number of CVS procedures carried out in the unit in a typical week, the preferred route (transabdominal [TA] vs transcervical [TC]), technique (use of local anaesthetic [LA] and needle technique). RESULTS: Response rate was 96.9%; TA was the preferred route (96.8%) in all centres except one. Single-needle technique is used exclusively in half the centres (51.6%). LA is used by most operators (90.3%) before the procedure. Three centres did not routinely use LA for CVS. CONCLUSIONS: Operators across the United Kingdom almost exclusively use the TA route for CVS with single-needle technique in 51.6% of cases. The use of LA prior to CVS is a very common practice in the United Kingdom.

Instruments for chorionic villus sampling for prenatal diagnosis.

BACKGROUND: Chorionic villus sampling (CVS) is the method of choice for obtaining fetal tissue for prenatal diagnosis before 15 weeks of pregnancy. CVS can be performed using either a transabdominal or transcervical approach. The type of instrument and technique used could have a significant impact on the outcome of the procedure. An ability to manoeuvre the instrument within the uterine cavity without puncturing the gestational sac, to see the tip of the instrument on ultrasound scanning and to minimise the number of instrument passes into the uterus are particularly important. OBJECTIVES: To compare the efficacy and safety of different instruments and techniques used to obtain chorionic tissue in early pregnancy by the transabdominal or transcervical route. Primary outcomes included failure to obtain an adequate sample (greater than 5 mg of chorionic villi), need for reinsertion of the instrument, pain, and miscarriage following the procedure. Secondary outcomes included mean weight of tissue obtained, successful culture, difficult instrument insertion, poor visualisation of instrument, vaginal bleeding following the procedure and cost per procedure. SEARCH METHODS: We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (31 August 2012). SELECTION CRITERIA: Randomised trials comparing different instruments (forceps, cannula, needle) or techniques for CVS using either transabdominal or transcervical approach. DATA COLLECTION AND ANALYSIS: Two review authors assessed eligibility and trial quality. MAIN RESULTS: For transcervical CVS, forceps and cannulae were evaluated in five trials involving 472 women. When a cannula was used, operators failed to obtain an adequate sample (greater than 5 mg of chorionic villi) more often (average risk ratio (RR) 3.81; 95% confidence interval (CI) 1.52 to 9.56). There was no difference in the need for reinsertion of instruments (average RR 2.44; 95% CI 0.83 to 7.20). However, inserting a cannula was more painful (RR 1.93; 95% CI 1.11 to 3.37). There was no difference in spontaneous miscarriage when the use of a cannula was compared with biopsy forceps (RR 1.00; 95% CI 0.14 to 6.96). One study reported the cost of the procedures and found CVS with a cannula to be more expensive (mean difference (MD) $183.7; 95% CI 152.62 to 214.78).When different types of cannulae for transcervical CVS were compared, a Portex cannula was more likely to result in an inadequate sample (RR 2.23; 95% CI 1.25 to 3.98) compared with the silver cannula and to result in a difficult (RR 3.26; 95% CI 1.38 to 7.67) or painful (RR 5.81; 95% CI 1.41 to 23.88) procedure when compared with the aluminium cannula.For transabdominal CVS, two trials comparing different needle techniques were included involving 285 women. One study using an ex vivo system of term placentae was excluded. The included trials compared different continuous negative pressure aspiration techniques with a discontinuous negative pressure system created by a syringe attached to a 20 gauge needle. The studies produced discrepant results. One study found there was no significant difference between groups in the mean weight of chorionic villi obtained (MD 0.40; 95% CI -2.25 to 3.05) or in failure to obtain an adequate sample (more than 5 mg of chorionic villi) on the first attempt (RR 1.02; 95% CI 0.54 to 1.93), whereas the other study found both of these outcomes to be significantly less favourable with the standard discontinuous technique using a syringe (mean weight of chorionic villi obtained: MD -14.80; 95% CI -21.71 to -7.89; failure to obtain an adequate sample on the first attempt: RR 2.73; 95% CI 1.08 to 6.92). There was no difference in rate of miscarriage following the procedure in either study (RR 7.15; 95% CI 0.37 to 136.50; RR 2.93; 95% CI 0.12 to 70.00). Perceived pain by the patient was similar between groups (MD 0.00; 95% CI -0.04 to 0.04) as was success of culture (no failed cases). AUTHORS' CONCLUSIONS: For transcervical CVS, although there is some evidence to support the use of small forceps instead of cannulae, the evidence is not strong enough to support change in practice for clinicians who have become familiar with a particular technique. For transabdominal CVS, based on current evidence, there is no difference in clinically important outcomes with the use of a continuous compared with a discontinuous negative pressure needle aspiration system.

First trimester transabdominal chorionic villus sampling--does the needle matter?

PURPOSE: To compare first-trimester transabdominal chorionic villus samples (TA-CVS) when obtained by 20-gauge amniocentesis versus lancet needles. METHODS: This is a retrospective study of all women with viable singleton pregnancies undergoing TA-CVS from 01/01/2009 to 03/31/2011. All CVS were performed by a single operator using a freehand technique and amniocentesis needles from 01/01/2009 to 08/31/2010 and lancet needles from 09/01/2010 to 03/31/2011. All samples were processed by the same laboratory. RESULTS: There were no differences between groups regarding maternal age, weight, gestational age at CVS, indication for CVS, uterine position, or placental location. Lancet needles were associated with significantly larger samples (median 18 [range 3-40] versus 7 [range 1-33] mg, p < 0.0001), more successful in situ hybridization (96% versus 74.2%, p = 0.03), and faster result reporting (median 7 [range 5-12] versus 9 [range 6-26] days, p = 0.002). CONCLUSIONS: Needle type may be clinically important when selecting 20-gauge TA-CVS needles.

10 años de experiencia en diagnóstico prenatal invasivo en el Instituto Dexeus / Invasive prenatal diagnostic practice: a review of a ten years experience at Dexeus Institut

Objetivos. Describir nuestra experiencia en la realización y resultados de las técnicas invasivas (TI) de diagnóstico prenatal (DP). Métodos. Se trata de un estudio descriptivo retrospectivo de las pacientes sometidas a una TI de DP desde enero de 1999 a diciembre de 2008, incluyendo todos los casos consecutivos de biopsia corial (BC) y amniocentesis (AC) genéticas. Resultados. Hemos analizado un total de 9.340 TI (8.928 AC y 412 BC). La edad gestacional ha sido de 15,9 (rango 10-38) y 11,6 (rango 9-16) semanas, respectivamente. Las principales indicaciones de referencia son la edad materna avanzada y la ansiedad. El porcentaje de cultivos no informativos ha sido de 0,49% para BC y 0,1% para AC. Se han diagnosticado un total de 380 anomalías cromosómicas (4,1%), 269 clínicamente relevantes. El valor predictivo positivo (VPP) para cromosomopatía relevante es del 2,9% (2,14% en la serie de AC y 19,6% en la serie de BC). El mayor VPP se obtiene ante las indicaciones de referencia ecográficas. Se han recogido un total de 88 complicaciones atribuibles a la TI (0,94%), con una tasa de pérdida fetal pos-procedimiento del 0,6%. La tasa de pérdida gestacional es del 0,9% (0,8% en la serie de AC y 4,3% en BC). Cuando analizamos los aspectos relacionados con la tasa de complicaciones y pérdidas fetales pos-procedimiento, únicamente el n.° de fetos, aspecto del LA, la indicación de la TI y la experiencia del operador son factores significativos. Conclusiones. El seguimiento y monitorización de las TI de DP constituye un primer paso en el proceso de control de calidad, recientemente introducido en la práctica médica en el área del diagnóstico prenatal(AU)

Objective. To describe invasive prenatal diagnostic practice in a single-center over a 10-years period. Methods. Included in this study were all consecutive pregnancies with genetic amniocentesis (AC) or chorionic villous sampling (CVS) procedure done during the period January 1999-December 2008. Results. A total of 8928 AC and 412 CVS were performed. Main indications for referral were increased maternal age and anxiety. The mean gestational age in which the procedure was done was 15,9 weeks (range 10-38) in AC and 11,6 weeks (range 9-16) in CVS. In this series, 380 cases of chromosome abnormalities (CA) were detectable by conventional cytogenetic analysis (4,1%), 269 of them considered clinically significant. The positive predictive value (PPV) for significant CA was 2,9%, 2,1% and 19,6% in the overall, AC and CVS group, respectively. The highest PPV were obtained for sonographic referral indications. A total of 88 complications during the 4 weeks’ period after the procedure were register (0,94%). The post procedural loss rate was 0,6% (0,4% after AC and 4,1% after CVS), 0,3% in singles and 1,6% in twin pregnancies AC group. The overall loss rate was 0,9% (0,8% in AC group, 4,3% in CVS group). There was a significant correlation between post procedure complications and number of fetuses, technical aspects (dark amniotic fluid), indications for referral and operator's experience. Conclusions. Monitoring of prenatal diagnostic invasive tests is the first step in the process of quality control, recently introduced into medical practice in the area of prenatal diagnosis(AU)

Reacción en cadena de la polimerasa cuantitativa y cultivo largo: ¿el mejor método para el estudio citogenético de muestras de vellosidad corial? / Quantitative Polymerase Chain Reaction and long term culture: the best method for cytogenetic study of chorionic villus sampling?

El diagnóstico prenatal citogenético durante el primer trimestre de gestación se realiza a partir de biopsias de vellosidad corial. Para la obtención de metafases se utilizan dos métodos: el cultivo corto o semidirecto (STC) y cultivo largo (LTC). La principal ventaja del STC es que no presenta contaminación materna y la del LTC es que no hay descritos en la literatura falsos negativos. Se considera que la combinación de las dos técnicas (STC y LTC) es la estrategia diagnóstica más eficaz para este tipo de estudios. La técnica de PCR cuantitativa fluorescente (QF-PCR) permite evaluar las aneuploidías más frecuentemente implicadas en el diagnóstico prenatal en 24-48 horas en muestras de vellosidad corial. El objetivo de este trabajo es evaluar la combinación de QF-PCR y LTC como sustituto de las clásicas STC y LTC para el diagnóstico prenatal en muestras de vellosidad corial. Para ello presentamos nuestra experiencia en 900 muestras de vellosidad corial(AU)

First trimester cytogenetic prenatal diagnosis is performed on chorionic villus biopsies. Two methods are used to obtain metaphases: the short-term or semi-direct culture (STC) and long term culture (LTC). The main advantage of STC is that there is no risk of maternal contamination, and of LTC that no false-negative findings are described in the literature. It is considered that the combination of the two techniques (STC and LTC) is the most effective diagnostic strategy for this type of study. The technique of quantitative fluorescent PCR (QF-PCR) allows the evaluation of aneuploidy most frequently involved in prenatal diagnosis in 24-48 hours in chorionic villus samples. The aim of this study is to evaluate the combination of QF-PCR and LTC as a substitute for classical STC and LTC for prenatal diagnosis in chorionic villus samples. We present our experience in 900 chorionic villus samples(AU)

The transvaginal probe as a uterine manipulator: a new technique to simplify transabdominal chorionic villus sampling in cases with difficult access to the trophoblast.

OBJECTIVES: To evaluate the efficacy of using the transvaginal probe to manipulate the uterus and change the position of the trophoblast, and to simplify access to the chorionic villus under difficult conditions. METHODS: One thousand five hundred and thirty-nine procedures were performed in our centre in 1524 pregnant women from September 2006 to September 2009. In 90 of these, a difficult access to the trophoblast was observed and uterine manipulation under continuous ultrasound guidance with a double needle technique, was applied to obtain the sample. Of these, 86 samples were taken from singleton pregnancies and 4 from two bichorionic twin pregnancies RESULTS: One thousand five hundred and thirty-nine transabdominal chorionic villus sampling (TA-CVS) procedures were conducted on 1524 pregnant women. As many as 1449 were performed without manipulation with the transvaginal probe and in 90 cases the manipulation was carried out. In 89 cases, access to the trophoblast was difficult and the uterus was manipulated, which enabled an adequate TA-CVS to be performed with a single aspiration. In one case, TA-CVS was not performed due to significant pelvic pain in a patient with a fixed, retroflexed uterus and a previous history of endometriosis. CONCLUSIONS: Uterine manipulation with the transvaginal probe may be a useful solution in cases where TA-CVS is limited by difficult access to the trophoblast.

Evaluation of the feasibility of a new method for performing chorion villus sampling.

OBJECTIVE: This study aimed to evaluate the usefulness and safety of a new method for taking a placental biopsy. METHODS: The procedures were performed using the traditional single needle technique (group 1) or the new method (group 2). In group 2, the piston was fixed in a simple metallic clip and the negative pressure was maintained in a continuous manner which was controlled with a three-way stopcock. RESULTS: Multiple uterine insertion was necessary in 14 cases (32.6%) in group 1 and five (11.9%) in group 2 (p < 0.05). The amount of chorionic tissue obtained was significantly higher in group 2 (19.1 +/- 15.0 mg vs. 33.9 +/- 17.4 mg p < 0.05). The abortion rates did not differ in either group. CONCLUSION: While using this technique, the operator is capable of performing the procedure without any assistance and of applying constant negative pressure only in the placenta. The advantageous outcomes are probably related to the size as well as the incessant fashion of the vacuum force.

A randomized study to assess two different techniques of aspiration while performing transabdominal chorionic villus sampling.

OBJECTIVE: The technique used to perform transabdominal chorionic villus sampling (CVS) is not standardized, but aspiration of villi is generally obtained by discontinuous vacuum created in a syringe, manually or by a hand-grip device. We evaluated the feasibility of a new method of performing CVS which employs a 4-mL Vacutainer connected to the needle, producing a continuous negative pressure. METHODS: Two hundred pregnant women, whose gestational age ranged from 10 + 2 to 16 + 2 (mean, 12 + 1) weeks, entered the randomized study, which was powered to detect with 90% probability the absence of any difference in the size of chorionic samples obtained by using a 20-mL syringe with the vacuum obtained by a hand-grip device (Group 1) or by a vacutainer (Group 2). Four operators with different levels of experience performed all the procedures, which were done transabdominally using a freehand technique with a 20-gauge needle under ultrasound guidance. RESULTS: Maternal age, body mass index, gestational age and the way the needle was inserted within the chorion were similar in the two groups. The median amount of villi sampled was 20 mg, with no differences between the two groups. The rate of fetal loss was 1.7%. All losses occurred in women of Group 1 who had only one needle insertion. A second needle insertion was required more frequently while using the vacutainer. CONCLUSION: This new technique for performing transabdominal CVS uses a readily available device and is as effective as traditional sampling systems to aspirate villi. It has the advantage of being a one-operator procedure.

Chorionic villus sampling for early prenatal diagnosis at Bhumibol Adulyadej Hospital.

OBJECTIVE: To evaluate results of chorionic villus sampling for early prenatal diagnosis at Bhumibol Adulyadej Hospital. DESIGN: Retrospective descriptive study. SETTING: Perinatal unit, Department of Obstetrics and Gynaecology, Bhumibol Adulyadej Hospital. SUBJECTS: Three hundred and eighty three women were enrolled to chorionic villus sampling at the perinatal unit, Department of Obstetrics and Gynecology, Bhumibol Adulyadej Hospital, from November 10,1997 to October 17, 2006. RESULTS: During the present study periods three hundred and eighty three women were recruited, of these chorionic villus sampling for chromosome diagnosis were performed on 355 while 6 were for abnormal Thalassemia screening. Twenty two cases were excluded because ultrasound examination showed anembryonic pregnancy or fetal demise in utero in 13 cases, multiple fibroids in 4 cases, large area of placental hemorrhage in 3 cases, 1 case of multiple pregnancy and in 1 case the placenta was in an inappropriate position. The most common indication was elderly gravidarum (95.84%). Other indications were abnormal Thalassemia screening, abnormal ultrasound findings, family chromosome disorder previous Down syndrome, and severe oligohydramnios. The authors found eleven cases of chromosome abnormalities, four cases of maternal cell contamination and three cases of failed tissue culture (two cases from transcervical chorionic villus sampling and one case from transabdominal chorionic villus sampling) and two cases of mosaicism. There were two fetal losses in the present study and all the babies from the normal chromosome result looked normal. Second trimester amniocentesis following chorionic villus sampling was required due to maternal cell contamination, mosaicism and failed tissue culture. (2.77%) All cases had follow-up ultrasound scan during 18-20 weeks. CONCLUSION: The authors found that chorionic villus sampling is a possible alternative technique for prenatal diagnosis of cytogenetic abnormalities and abnormal Thalassemia screening in Thailand. It probably has a slightly higher rate of failed tissue culture and maternal cell contamination than amniocentesis, but it is generally done earlier in pregnancy than amniocentesis and is particularly advantageous for detecting certain genetic conditions.

Pain experience during chorionic villus sampling and amniocentesis: a preliminary study.

OBJECTIVE: To investigate the maternal perception of pain before and after amniocentesis (AC) or transabdominal chorionic villus sampling (TA-CVS). STUDY DESIGN: Three hundred women were divided into groups of 100 participants destined to undergo three different fetal sampling procedures: amniocentesis (group 1), transabdominal chorionic villus sampling (CVS) with a 19 gauge Blache needle (group 2) and transabdominal CVS with a 20 gauge needle (group 3). The visual analog scale (VAS) was used to quantify the patient's pre-sampling expected pain level and the real pain level was measured immediately after the sampling procedure. The factors liable to influence the VAS score after the sampling procedure were studied by single and multivariate analysis and concerned either the sampling procedure or patient demographic data. RESULTS: The VAS scores obtained before the procedure were not significantly different for the three sampling groups. When performed with a 19 gauge Blache needle TA-CVS is significantly more painful than the other sampling procedures (p=0.0002): VAS score of 3.62 (group 2), 2.49 (group 3) and 2.68 (group 1) for CVS with 20 gauge needle and amniocentesis. Multivariate analysis identified a group of patients for which the perception of pain induced by sampling was higher compared to the other patients: nulliparous patients, having undergone 19 gauge Blache needle CVS, with a high pre-sampling VAS score. CONCLUSION: Transabdominal chorionic villus sampling with a 19 gauge Blache needle seems to be the most painful sampling procedure. We question the need to use a 19 gauge needle as acceptable results are obtained with a 20 gauge needle.

Transabdominal chorionic villus sampling (CVS) for prenatal diagnosis of genetic disorders.

OBJECTIVE: To determine the safety and outcome of transabdominal Chorionic Villus Sampling (CVS) for prenatal diagnosis of genetic disorders. DESIGN: Descriptive study. PLACE AND DURATION OF STUDY: Department of Pathology, PNS Shifa, Karachi, from January 2003 to December 2004. PATIENTS AND METHODS: A total of 143 couples with request for prenatal diagnosis of various genetic disorders were studied. Transabdominal CVS was done under local anesthesia and ultrasound guidance. A Co-axial Chorion Biopsy needle set with an outer guide and an inner aspiration needle was used. The needle was introduced into the placenta in its longitudinal direction. Once the needle was adequately placed, the chorionic villi were aspirated with a to and fro jiggling movement of the aspiration needle and a suction force was applied through a syringe. Results were recorded and analyzed for descriptive statistics. RESULTS: A total of 144 CVSs were done in the outdoor on 143 couples including one with a twin pregnancy. The most common indication was b-thalassaemia (97%). Most procedures (76%) were done between 12 and 14 weeks (range 10-21 weeks). All placental positions including 52% anterior and 48% posterior were approachable through the trans-abdominal route. Most aspirations were easy, however, in 28% the aspiration was difficult due to a variety of factors. The overall success rate was 100%. In 85% of the cases sample yield was >25mg while in the remaining cases 10-25mg of sample was obtained that allowed a comfortable diagnosis. The procedure related abortion occurred in 1/144 (0.7%). CONCLUSION: Transabdominal CVS is a useful outdoor procedure for prenatal diagnosis. Placentae in almost any position can be approached without significant risk to the mother and the fetus.

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. 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.

The influence of needle and syringe size on chorionic villus sampling of term placentae: a randomised trial.

OBJECTIVE: To determine the effect of needle and syringe size on the amount of tissue obtained at chorionic villus sampling METHODS: Two needle sizes, 18 and 20 gauge, and two syringe sizes 5 mL and 20 mL, were used to assess samples from term post-partum placentae. Each of the four combinations was tested by 25 aspirations. The placentae were divided into 100 grid spaces and each grid space was randomly allocated to a needle/syringe combination. The resulting samples were cleaned to separate the chorionic villi (CV), centrifuged and then weighed. RESULTS: Significantly more tissue was obtained with an 18-g needle compared with a smaller 20-g needle (median weight difference 1.5 mg, 95% CI 0.8-2.3 mg). More tissue was also obtained with the larger 20-mL syringe though the impact of the syringe size was less than that of the needle size (median difference 0.8 mg, 95% CI 0-1.6). CONCLUSION: A larger syringe and needle size yields a larger quantity of chorionic villi from the post-partum term placenta.

Instruments for chorionic villus sampling for prenatal diagnosis.

BACKGROUND: Chorionic villus sampling (CVS) is the method of choice for obtaining fetal tissue for prenatal diagnosis before 15 weeks of pregnancy. CVS can be performed using either transabdominal or transcervical approach. The type of instrument used could have a significant impact on the success rate of the procedure. An ability to manoeuvre the instrument within the uterine cavity without puncturing the gestational sac, and to see the tip of the instrument on ultrasound scanning are particularly important. OBJECTIVES: The objective of this review was to assess the effects of instruments used to obtain chorionic tissue in early pregnancy by transabdominal or transcervical route (chorionic villus sampling). The outcomes of interest were technical difficulties during the procedure, quality and quantity of obtained tissue, maternal adverse effects, pregnancy outcome and cost-effectiveness. SEARCH STRATEGY: The Cochrane Pregnancy and Childbirth Group trials register was searched. Date of last search: November 2002. SELECTION CRITERIA: Randomised trials comparing different instruments (forceps, cannula, needle) for chorionic villus sampling using either transabdominal or transcervical approach. DATA COLLECTION AND ANALYSIS: Eligibility and trial quality were assessed by two reviewers. MAIN RESULTS: There were no trials comparing instruments for transabdominal CVS. Forceps and cannula were evaluated in five transcervical CVS trials involving 472 women. When a cannula was used, operators obtained an inadequate sample (less than 5 mg) more often (relative risk (RR) 4.21, 95% confidence interval (CI) 2.15 to 8.25). Compared with forceps, cannulae had to be re-inserted more often (RR 2.98, 95% CI 1.62 to 5.47). Also, inserting a cannula was more painful (RR 1.93, 95% CI 1.11 to 3.37). One study reported the cost of the procedures and found CVS with cannula to be more expensive (weighted mean difference $183.7, 95% confidence interval 152.62 to 214.78). When different types of cannulae were compared, Portex cannula was more likely to result in an inadequate sample and a difficult or painful procedure when compared with either the silver or aluminum cannula respectively. REVIEWER'S CONCLUSIONS: Although there is some evidence to support the use of small forceps for transcervical chorionic villus sampling, the evidence is not strong enough to support change in practice for clinicians who have become familiar with aspiration cannulae.