Chapter 24: CHORIONIC VILLUS SAMPLING

INTRODUCTION

Sonographically guided chorionic villus sampling (CVS) has been available in the United States since the early 1980s and has offered couples at genetic risk an early and rapid prenatal diagnosis.¹ The procedure, which can be performed as early as 10 weeks of menstrual age, provides preliminary cytogenetic results within 48 hours and final culture results within 7 days. In contrast, genetic amniocentesis is not routinely performed until approximately 16 weeks of menstrual age with an additional 7 to 10 days required to culture the amniotic fluid cells. Fluorescent in situ hybridization (FISH) can be used for both of these techniques. Thus, the pregnancy is nearly half completed before a definitive diagnosis can be established with amniocentesis. If a significant fetal abnormality is identified, the prospective parents must make a difficult choice of whether to continue or terminate the pregnancy. Postponing this decision until the mid-trimester is extremely difficult because fetal movement has been perceived and significant bonding between the parent and fetus has occurred. In addition, the pregnancy is public knowledge, thereby precluding an element of privacy in decision making. If termination is chosen, maternal risks are greater than in the first trimester, with maternal mortality being up to 5 times higher.²

Despite the advantages of CVS, the procedure has struggled to become universally accepted. This has been due predominantly to a perception that the sampling and laboratory procedures are more complex than amniocentesis. In addition, there have been concerns that the procedure may induce fetal limb defects. Recently, however, enthusiasm for CVS has been renewed. First, contemporaneous studies have demonstrated the accuracy of the laboratory results, the reliability of the sampling, and the safety of the procedure if performed after 10 weeks of gestation by experienced operators. Second, studies have established the superior safety to CVS over first trimester amniocentesis.^{3,4, and 5} Additionally, over the last decade, the complication rates of CVS and mid-trimester amniocentesis are comparable due to the reduction of CVS problems.⁶ Third, the recent success of first trimester screening for fetal chromosomal abnormalities provides an impetus for a first trimester diagnostic procedure for fetal karyotype.⁷

CONCEPTS AND INDICATIONS FOR CHORIONIC VILLUS SAMPLING