Traditionally, chorionic villus sampling (CVS) has been used for diagnosis of genetic abnormality at an earlier gestational age than amniocentesis. More recently, interest has been growing in using either procedure at 11 to 14 weeks’ gestation. Philip and colleagues studied the comparative safety and efficacy of the two techniques at 11 to 14 weeks’ gestation in a large study involving 14 centers in the United States, Canada, and Denmark.

They studied women seeking genetic diagnoses because of advanced maternal age (older than 34 years), history of fetal trisomy, or positive screening. Ultrasonography was used to determine gestational age. Excluding factors included multiple pregnancy, serious maternal illness, bleeding disorders, and recognized fetal abnormality. After ultrasonography, the mothers were randomized to amniocentesis or CVS. Operators were required to have completed at least 25 of each type of procedure between 77 and 104 days of gestation and to follow standard procedures. The main study outcome was fetal loss or preterm delivery before 28 weeks’ gestation in normal pregnancies. The study also assessed fetal loss, neonatal deaths, oligohydramnios, gestational age at delivery, intrauterine growth restriction, respiratory distress syndrome, and congenital malformations.

The 1,914 women assigned to CVS were comparable to the 1,861 women assigned to amniocentesis, except that 44.6 percent of the CVS group had had a previous miscarriage or preterm birth compared with 39.7 percent of the amniocentesis group. Cytogenetic abnormalities were diagnosed in 72 pregnancies (34 in the CVS group and 38 in the amniocentesis group). Pregnancy outcome data were available for 3,698 cytogenetically normal pregnancies. The rate of loss or delivery before 28 weeks was comparable in the two groups. Amniocentesis was associated with a slightly higher rate of spontaneous loss before 20 weeks, procedure-related terminations, and early leaking of amniotic fluid. Cramping after the procedure was significantly more common with CVS. The rate of talipes equinovarus (clubfoot) was low but increased fourfold after amniocentesis (0.16 percent for CVS; 0.66 percent for amniocentesis), and most cases required surgical correction. The rate of talipes equinovarus was significantly increased in cases in which amniotic fluid leakage was observed.

The authors conclude that, compared with CVS, amniocentesis in cytogenetically normal pregnancies at 13 weeks has an increased risk of talipes equinovarus. This risk appears to be related to the stage of gestation and the loss of fluid during and after the procedure. Amniotic fluid loss following amniocentesis also appears to be related to a slight increase in early pregnancy loss.