Instruments to use for chorionic villus sampling for prenatal diagnosis

More research is needed to identify the best surgical instruments and techniques to use for chorionic villus sampling testing during early pregnancy (before 15 weeks).

Chorionic villus sampling (CVS) is a test where a small piece of placental tissue (chorion) is removed from the pregnant woman's womb (uterus) and used for testing for genetic disorders. The tissue can be removed through the cervix or through the abdomen using plastic or metal tubes (cannulae), biopsy forceps or fine needles. The woman's risk of miscarriage increases if several attempts are needed to obtain sufficient placental tissue or the gestational sac is damaged during the procedure using ultrasound guidance.

The review found there is some evidence that small forceps may be more effective and less painful for the woman than using an aspiration cannula for sampling through the cervix (transcervical CVS). However, there was no difference in risk of miscarriage. When sampling was obtained through the abdomen (transabdominal CVS) using a needle with either a continuous or discontinuous negative pressure aspiration system, there was no difference in the effectiveness of the techniques, the amount of pain or in the risk of miscarriage. Forceps and cannulae were evaluated in five transcervical CVS trials involving 472 women. Two trials involving 285 women compared different needle techniques for transabdominal CVS. These randomised trials are too small to provide reliable evidence in favour of one particular instrument or technique for transcervical or transabdominal chorionic villus sampling.

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.

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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 strategy: 

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).

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