Chromosome Analysis, Amniotic Fluid

Fetal loss rate at 14 to 18 week sampling is considered to be 0.5%, and 2% to 3% at 10 to 13 weeks.¹ Chorionic villus sampling (CVS) may be safer than early amniocentesis for early prenatal diagnosis of cytogenetic abnormalities.^2,3 The risk of miscarriage with CVS is 1% to 1.5% but the risk of maternal infection appears to be higher with CVS than with amniocentesis.⁴ Cytogenetic analyses using such samples allow for an early gestational testing based on a 10- to 11-week placental biopsy and a five-day cytogenetic study. Most failures are due to an inappropriate biopsy containing only maternal decidua. Chromosomal aberrations were found in 4.6% of fetuses in women older than 38 to 40 years of age. Trisomy 21 was the most common abnormality (62%). Klinefelter syndrome (11%) and Edwards syndrome, trisomy 18 (11%) were next most frequent in the cases of advanced maternal age.

Prenatal diagnosis is possible for more than 1000 inherited diseases. Most are inherited in an autosomal recessive manner. Antenatal diagnosis using gene probes has become available for cystic fibrosis, muscular dystrophy, sickle cell anemia, hemophilia, and many other genetic abnormalities. This can be done from either cultured amniotic fluid cells or chorionic villous sampling.⁵