Extraction of DNA from chorionic villi

Antenatal diagnosis by DNA analysis is almost ten years old (Kan et al., 1976; Orkin et a1.,1978; Kan and Dozy, 1978). These analyses used cultured amniocytes as the source of fetal DNA. Cultures are established at about the sixteenth week of pregnancy and some two to three weeks are needed to allow the cells to replicate so that there are sufficient to enable DNA to be extracted in usable quantities. The analysis of the DNA obtained in this way takes perhaps a week (although this may be reduced, Law et al., 1984). If everything goes well a result should be available at about 19–20 weeks gestation. Such a time-scale serves to demonstrate the special advantage of chorion villus sampling (CVS) because using such tissue fetal DNA (and chromosomes) can be obtained and analysed within the first trimester.