What is the difference between chorionic villus sampling and amniocentesis

For example, from through , the major complication rate was 0. However, the risk for developing major complications from abortion at any gestational age decreased during the s. More contemporary national morbidity data based on current abortion practices are not yet available. CDC surveillance data also indicate an increase in the risk for maternal death with increasing gestation.

From through , the risk for abortion-related death was 1. The lower risk associated with first-trimester abortions may be an important factor for prospective parents who are deciding between CVS and amniocentesis. Amniocentesis is usually performed at weeks' gestation, but more amniocentesis procedures are now being performed at weeks' gestation. Adjusting for confounding factors such as gestational age, the CVS-related miscarriage rate is approximately 0. Although uterine infection i.

In one study, no episodes of septic shock were reported after 4, CVS procedures, although less severe infections may have been associated with 12 of the 89 observed fetal losses 5. Overall infection rates have been Cytogenetically ambiguous results caused by factors such as maternal cell contamination or culture-related mosaicism are reported more often after CVS than after amniocentesis 2. In these instances, follow-up amniocentesis might be required to clarify results, increasing both the total cost of testing and the risk for miscarriage.

However, ambiguous CVS results also may indicate a condition e. Thus, in these situations, CVS may be more informative than amniocentesis alone. CVS Certain congenital defects of the extremities, known as limb deficiencies or limb-reduction defects, have been reported among infants whose mothers underwent CVS.

This section addresses 1 the expected frequency and classification of these birth defects, 2 the physical features of reported infants in relation to the timing of associated CVS procedures, and 3 cohort and case-control studies that have been done to systematically examine whether CVS increases the risk for limb deficiencies. Population-based studies indicate that the risk for all limb deficiencies is from per 10, live births Limb deficiencies usually are classified into distinct anatomic and pathogenetic categories.

The most common subtypes are transverse terminal defects, which involve absence of distal structures with intact proximal segments, with the axis of deficiency perpendicular to the extremity.

Transverse deficiencies occur as either isolated defects or with other major defects. Although the cause of many isolated limb deficiencies and multiple anomalies that include transverse deficiencies is unknown, researchers have hypothesized that these deficiencies are caused by vascular disruption either during the formation of embryonic limbs or in already-formed fetal limbs 17, Reports of clusters of infants born with limb deficiencies after CVS were first published in Three studies illustrate the spectrum of CVS-associated defects Data from these studies suggest that the severity of the outcome is associated with the specific time of CVS exposure.

Exposure at greater than or equal to 70 days' gestation has been associated with more limited defects, isolated to the distal extremities, whereas earlier exposures have been associated with more proximal limb deficiencies and orofacial defects. For example, in a study involving 14 infants exposed to CVS at days' gestation and examined by a single pediatrician, 13 had isolated transverse digital deficiencies In another study in Oxford of five infants exposed to CVS at days' gestation, four had transverse deficiencies with oromandibular hypogenesis In a review of published worldwide data, associated defects of the tongue or lower jaw were reported for 19 of 75 cases of CVS-associated limb deficiencies Of those 19 infants with oromandibular-limb hypogenesis, 17 were exposed to CVS before 68 days' gestation.

Cohort studies usually measure rates of a specified outcome in an exposed group compared with an unexposed group. Ideally, both groups should be selected randomly from the same study population. The three largest collaborative trials of CVS in Europe, Canada, and the United States were designed originally in this way; however, in these studies, the outcome of interest was fetal death.

The report of the first U. After the initial case reports in , neonatal outcomes from the collaborative trials were analyzed more intensively However, rather than comparing rates for limb defects in the CVS-exposed cohorts with those of amniocentesis-exposed cohorts from the same study population, the rates in the CVS groups were compared with population-based rates.

Consequently, these comparisons must be interpreted with caution because population-based rates are derived differently i. CVS-associated risk for limb deficiencies could be underestimated by these comparisons if follow-up of pregnancies in the exposed cohort is incomplete. Other epidemiologic issues must also be considered when interpreting comparisons of crude rates.

Unless a formal meta-analysis is performed, these comparisons neither account for heterogeneity between studies nor assign individual "weights" to studies. Comparisons of crude rates also do not adjust for potential confounding variables, such as maternal age. Methods of anatomic subclassification also vary between registries and can differ from methods applied to CVS-exposed cohorts.

In addition, comparing overall rates of limb deficiency in groups exposed to CVS with groups unexposed to CVS might overlook an association with a specific phenotype, such as transverse deficiency. These rates include studies that describe affected limbs in sufficient detail to exclude nontransverse defects.

Rates calculated for the smaller cohorts i. The range of rates for these two populations 1. The threefold to fivefold increase in the overall rate for the 65 centers compared with the rates for Victoria or Boston is statistically significant chi-square: p Investigators participating in the International Registry also have combined birth-defect data from multiple CVS centers, including some of the 65 CVS centers 16, An abstract published in includes information about , procedures reported to the International Registry.

The rate of transverse deficiencies in the reporting centers was 1. Different methods of classification. The method of classification of limb deficiencies for the International Registry resulted in a smaller proportion of transverse deficiencies compared with all limb deficiencies than some population based studies 17,32,36, The reason for this smaller proportion is that the definition of "transverse terminal deficiencies" is more restrictive and includes only defects that extend across the complete width of a limb and excludes terminal deficiencies of fewer than five digits.

Ascertainment of outcomes. Ascertainment of outcomes may be incomplete in CVS registries because deliveries can occur at a hospital remote from where the CVS was performed and might not be reported back to the CVS center. The effect of this incomplete ascertainment would be to underestimate risk for adverse outcomes. Differences among centers in the performance of CVS.

Investigators have compared rates of miscarriages and rates of limb deficiencies at individual facilities. This comparison is based on the assumption that the causes of both miscarriage and limb defects might be related to particular techniques of sampling by individual obstetricians. The association between high miscarriage and limb-deficiency rates in one U. CVS center was cited as potential evidence of the role of surgical inexperience A cluster of limb deficiencies in another U.

Case-control approaches with a minimum of case and control patients have greater statistical power than cohort studies of 10, or fewer births to detect a fourfold increase in risk for transverse deficiencies the degree of relative risk suggested by data from the 65 CVS centers Previous: FDA Advisories. Next: Toxoplasmosis in Pregnancy. Oct 15, Issue. Am Fam Physician. What is prenatal diagnosis?

Do all pregnant women have these tests? What is amniocentesis? What is CVS? When are the tests done? Is one test better than the other? Are there risks involved with these tests? Read the full article.

Get immediate access, anytime, anywhere. Choose a single article, issue, or full-access subscription. Earn up to 6 CME credits per issue. Purchase Access: See My Options close. Discuss the options with your doctor. Amniocentesis or CVS is done when there is an increased risk that the baby may have genetic disorders or birth defects. Before either procedure, you may have counseling with a genetic expert. This allows you to learn about the conditions the test may find. You will have a better idea of what those mean for you and your baby.

In this procedure, a sample of amniotic fluid fluid around the baby is removed from your uterus. A doctor inserts a long, thin needle through your abdomen into your uterus. He or she withdraws a small amount of fluid. The fluid is sent to a laboratory for evaluation. In the lab, the fluid can be tested for:.

Your body will make more fluid to replace the fluid that is taken out. The baby will not be hurt during the procedure. Some women feel mild cramping during or after the procedure. Your doctor may tell you to rest on the day of the test. Usually you can resume normal activity the next day. CVS removes a small sample of placenta tissue from the uterus. The sample is then sent to the lab for testing. The sample can be taken 2 ways:.

Local anesthesia is used for this test to reduce pain and discomfort. Most women feel fine after the test. Some may have mild bleeding spotting afterward. Amniocentesis is usually performed during the 15th week of pregnancy or later.

CVS is usually performed between the 10th and 13th weeks of pregnancy. Royal College of Obstetricians and Gynecologists. Please note: we will endeavour to respond to your enquiry within five 5 business days. Follow us on. Chorionic villus sampling CVS and amniocentesis Chorionic villus sampling CVS and amniocentesis are tests performed in pregnancy to identify chromosomal abnormalities such as Down syndrome or genetic conditions such as cystic fibrosis. Reasons for having CVS or amniocentesis Women may choose to have a CVS or an amniocentesis if: the results from a screening test showed the baby to be at high risk for a chromosomal abnormality they require certainty regarding the diagnosis of Down syndrome or another chromosomal abnormality or genetic condition an ultrasound during their pregnancy has identified an abnormality in the baby there is a known family history of a genetic disorder.

Chorionic villus sampling CVS CVS is performed at 11 to 14 weeks of pregnancy by taking a small sample of placental tissue chorionic villi. Transabdominal CVS The procedure is performed under local anaesthetic which numbs the area of skin prior to inserting the needle.

The risk of pregnancy loss due to a transcervical CVS is up to two per cent one in procedures. Light bleeding can occur after a CVS but usually settles without further problems. In one per cent of cases, a CVS result may be difficult to interpret due to a situation called mosaicism. This uncertainty can be resolved by performing an amniocentesis. In rare cases a result can not be provided from a CVS and repeat sampling may be required. Amniocentesis Amniocentesis is performed after 15 weeks of pregnancy by taking a sample of amniotic fluid that surrounds the baby.

Risks associated with amniocentesis The risk of pregnancy loss due amniocentesis is one in procedures. Infection following amniocentesis is very rare and occurs in less than one in procedures performed.

In rare cases a result can not be provided from amniocentesis and repeat sampling may be required.