Risks of chorionic villus sampling and amniocentesis
CVS and amniocentesis are ultrasound-guided procedures performed for prenatal diagnosis of chromosomal abnormalities, genetic disorders and other abnormalities. Data suggests that transabdominal CVS and amniocentesis have equivalent loss rates.
CVS and Amniocentesis
- CVS is a procedure in which a small sample of placental tissue (chorionic villi) is obtained either transcervically (TC) or transabdominally (TA) under ultrasound guidance. It is performed generally between 10-13 weeks of gestation.
- Amniocentesis refers to the removal of amniotic fluid by placing a needle into the amniotic cavity under ultrasound guidance. It is usually performed between 15-18 weeks gestational age for prenatal diagnosis of genetic disorders.
Advances in first-trimester aneuploidy screening have increased the need for early prenatal diagnosis, and CVS in the only diagnostic test currently available in the first trimester. However, CVS is not widely utilized, partly because of its limited availability, and partly because of the perception that CVS confers increased risks compared with amniocentesis.
Fetal loss rates following CVS and amniocentesis are often difficult to estimate, as large populations have not been followed from early pregnancy to provide accurate background loss rates of pregnancy. The majority of data are from studies comparing loss rates in patients undergoing CVS with those under amniocentesis. These studies looked at total pregnancy losses. The total pregnancy loss rate in necessarily higher following CVS than amniocentesis, because CVS is performed at an earlier gestational age, when the risk of spontaneous loss is higher. A Cochrane review found that the total pregnancy loss rate following TA CVS was equivalent to that of 2nd trimester amniocentesis, whereas TC CVS was associated with a slightly higher risk of miscarriage. The most recent systematic review demonstrated pregnancy loss rates for CVS vs. amniocentesis to be 0.7% vs. 0.6% within 2 weeks post-procedure, 1.3% vs. 0.9% up to 24 weeks, and 2.0% vs. 1.9% for the entire pregnancy, suggesting similar risks. Several nonrandomized observational studies suggest that loss rates from either TA CVS or amniocentesis are somewhat similar to those in women not undergoing invasive procedures. Specifically for amniocentesis more recent literature, although not perfect, suggests that loss rates appear no higher than 1/300-1/500 or even 1/1000, and may be even lower in experienced centers.
- Limb-reduction defects after CVS: current evidence suggests that performing CVS between 10 and 13 weeks does not increase the risk of limb reduction defects
- Leakage of amniotic fluid(AF) after amniocentesis: 1.7% of pregnancies may experience AF leakage after amniocentesis compared with 0.4% controls, although other practitioners quotes even lower figures. The fluid leakage usually stops within 1 week, with normalization of AF volume within 3 weeks. Perinatal survival is reported in > 90% of cases.
OB-GYN, Sub-specialist, Certified Nurse Midwife and Laborist
Retired SMFM Document