Fetal karyotyping by chorionic villus sampling after the first trimester

Area of Science:

• Prenatal Diagnosis
• Cytogenetics
• Reproductive Medicine

Background:

• Chorionic villus sampling (CVS) is a common first-trimester prenatal diagnostic technique.
• Karyotyping is essential for detecting chromosomal abnormalities in fetuses.
• Evaluating CVS efficacy beyond the first trimester is crucial for clinical decision-making.

Purpose of the Study:

• To assess chorionic villus sampling (CVS) for karyotyping after the first trimester.
• To determine the incidence of result failure, confined placental mosaicism, and diagnostic errors at various gestational ages.
• To compare the utility of CVS with alternative methods in later pregnancy.

Main Methods:

• Retrospective analysis of 2424 CVS results from 1989-1997.
• Categorization of samples based on gestational age at sampling (8-14, 15-20, 21-28, and >29 weeks).
• Evaluation of direct preparation and cell culture methods, focusing on failure rates, confined placental mosaicism, and false results.

Main Results:

• No significant difference in failed direct preparation rates across gestational age groups (3.8%-6.6%).
• Significantly higher incidence of confined placental mosaicism after 21 weeks gestation compared to before 14 weeks.
• Low rates of false positive (6) and false negative (1) results with no significant gestational age dependency.

Conclusions:

• CVS remains a valuable tool for rapid prenatal karyotyping after the first trimester.
• After 20 weeks gestation, cordocentesis may be a preferable option due to a higher rate of cytogenetic discordancy between placenta and fetus.
• Gestational age influences the risk of confined placental mosaicism, impacting diagnostic accuracy.