RESUMEN
OBJECTIVES: To analyze chromosomal abnormalities according to patient's age and indications of patients in midtrimester amniocentesis for prenatal genetic diagnosis. METHODS: We retrospectively analyzed 1,565 cases of midtrimester prenatal genetic amniocentesis cases which were done in the cytogenetics laboratory at Kangnam St. Hospital, Catholic University Medical College from November1997 to May 2000. RESULTS: In 1,565 cases, the most common maternal and gestational age distributions were 35 to 39 years old and 17 to 17+6 weeks (32.78% and 21.47%, respectively). Abnormal maternal serum markers were the most common indication for amniocentesis (43.64%), and followed by advanced maternal age (40.45%) and abnormal ultrasonographic findings (3.64%). The overall incidence of chromosomal abnormalities was 4.47% (70 cases), of which numerical abnormalities and structural abnormalities were 1.86% (29 cases) and 2.61% (41 cases), respectively. Among the autosomal abnormalities, Down syndrome was most common (10 cases, 0.65%), and followed by Edward syndrome (9 cases, 0.59%). Among the sex chromosomal abnormalities, both of 47,XXX and 47,XXY were most common (3 cases, 0.20%, respectively). Chromosomal abnormalities were most frequently noted in the maternal age of 25 to 29 years old (5.10%), 30 to 34 years old (4.82%), 40 to 44 years old (4.31%), and followed by 35 to 39 years old (3.90%). On the other hand, chromosomal abnormalities were most frequently noted in abnormal ultrasonographic findings (7.02%), previous history of aneuploidy (5.88%), and followed by advanced maternal age (3.95%). CONCLUSION: This study suggested that although advanced maternal age is still important indication in midtrimester amniocentesis for prenatal diagnosis, abnormal maternal serum markers and ultrasonographic findings might be also important as indications. Therefore, they should be considered in prenatal genetic counseling.