Culture and Karyotyping of Amniotic Fluid Cells

Abstract

Introduction Prenatal diagnosis for an increasing variety of genetic disorders and congenital defects has been possible since about 1970. During the last decade the demand for prenatal diagnostic services has increased almost logarithmically and has become an overwhelming service load for many cytogenetic laboratories. This demand will probably continue to grow during the 1980s. Requests for chromosome studies are the most common. followed by requests to diagnose errors of morphogenesis (mostly neural tube defects), inborn errors of metabolism, and other Mendelian disorders. The most common indication for a prenatal cytogenetic study is advanced maternal age, which has an associated increased risk for trisomy 21 (Down syndrome) and other aneuploid conditions (Table 1). Prenatal diagnosis is indicated for pregnant women 35 years of age or more. The incidence of trisomy 21 is greater in amniotic fluid samples than at birth partly because about 65% of trisomy 21 fetuses abort spontane~usly,~ many after the 16th week of gestation.= Couples who have had a child with karyotype abnormality may be at increased risk in subsequent pregnancies; the recurrence risk for trisomy 21 is about 1 % . Individuals who carrv a balanced chromosome rearrangement are also at risk of having offspring or abortuses with unbalanced karyotypes. The risk of the amniocentesis procedure to the mother and fetus has been the subiect of considerable discussion. Only about 2% of women experience apparent complication such as vaginal bleeding, leakage of amniotic fluid, or abdominal cramping. The chance of miscarriage or problems associated with labor and delivery have not been shown to be significantly increased, and injury to the fetus from the needle appears very rare. A study undertaken in the United States concluded that