Direct vision chorion biopsy and chromosome-specific DNA probes for determination of fetal sex in first-trimester prenatal diagnosis.

Fetal sex was determined prenatally by molecular analysis of DNA from chorionic biopsy specimens taken in the first trimester of pregnancy. Single villi were obtained transcervically under direct vision with ultrasound guidance. The results of restriction endonuclease analysis of Y-chromosome-specific DNA from the biopsy specimens of 13 patients were confirmed in all cases by fetal karyotype analysis of cultures of biopsy specimens taken in parallel and of cultures of the products of conception. Prenatal sex determination by this method takes only 3-4 days and is not subject to the same errors as F-body identification.