RAPID KARYOTYPING IN THE 2ND-TRIMESTER AN D 3RD-TRIMESTER - RESULTS AND EXPERIENCES

Rapid karyotyping in the second and third trimester is an increasing f ield of collaboration between womens hospitals and humans genetics. Te chniques available for rapid karyotyping are: 1. Amniocentesis; to obt ain amniotic fluid cells for culturing and subsequent chromosome harve sting using the pipette method or the ,,in situ'' technique. The avera ge time between preparation of the amniotic fluid and the verbal notif ication of the analysed karyotype is 4.65 days for the pipette method and 5.97 days for the ,,in situ'' technique. The major advantages are that amniocentesis can be handled safely by many gynaecologists, and t he amniotic fluid samples can be posted easily to cytogenetic units fa miliar with rapid karyotyping. The main disadvantage is that currently only a few laboratories are able to handle the pipette method or the ,,in situ'' technique for rapid karyotyping. 2. Fetal blood sampling ( cordocentesis); and subsequent chromosome analysis on cultivated fetal lymphocytes leading to results within 2 to 4 days. The main advantage of this procedure is the reliability of the results obtained. Fetal b lood sampling, however, is restricted to specialists; this may involve scheduling delays. 3. Placental biopsy; with subsequent direct prepar ation and long term culturing. In comparison to both other techniques this procedure is faster if direct preparation is used. Results can be obtained even on the same day. The main disadvantage, however, is the problem with reliability of the direct preparation results. They must be confirmed by timeconsuming long-term culturing. Data are presented on the likelihood of abnormal ultrasound findings being caused by chr omosomal aberrations. These findings include hydramnios, oligohydramni os, growth retardation, fetal effusions, neural tube defects, craniofa cial defects, heart defects, gastroschisis and omphalocele, gastro-int estinal tract defects, urogenital defects, and limb defects. In future , such data needs to contain larger numbers of cases for each week of gestation. This well lead to better risk evaluation in each case with abnormal ultrasound findings and for those then requiring rapid karyot yping, to better management of these pregnancies at risk.