[Cytogenetical prenatal diagnosis by amniocentesis during the II and III gestation trimesters in Costa Rica]

The identification of fetal abnormal chromosomes in high risk pregnancies allows proper pediatric and obstetric management of the cases as well as genetic counseling. The results of 842 genetic amniocentesis from 1986 to 1999 are reported. All procedures were performed transabdominally and under ultrasound guidance, in hospitals of the social security system and in private facilities. There were two main reasons for referral: abnormal ultrasound assessment (48% of cases) and advanced maternal age (35%). Most procedures (66%) were performed during the second trimester of pregnancy and 34% during the third trimester. Fetal cells were closed cultured and suspension harvested. Median turn around time was 14 days. In 217 amniotic fluid samples no diagnosis could be obtained, mainly due to absence of cell growth in late gestation samples or because of blood contamination. Of 625 fetal karyotypes 55 (9%) were abnormal, due to 33 trisomies (including a Robertsonian translocation trisomy 13), eight cases of monosomy X, three mosaics (including a mosaic trisomy 22), balanced and unbalanced translocations, extra structurally abnormal chromosomes and other defects. Pseudomosaicism was detected in five cases. Taking into account the reason for referral, cases studied as a result of abnormal ultrasound assessment exhibited 17% abnormal karyotypes, in contrast to 2.5% cytogenetic defects in pregnancies of women 35 years or older. Prenatal cytogenetic and sonographic findings correlated with the phenotype of the newborn in 211 cases available for follow-up. Prenatal diagnosis of fetal defects allowed genetic counseling as well as better obstetric management and pediatric care. Normal results of both tests provided reassurance to prospective parents.