Culture of bloody amniotic fluid for chromosome analysis: an improved method.

Contamination of amniotic fluid samples with maternal or fetal red blood cells occurs in approximately 500 of amniocenteses. Culturing these samples for fetal chromosome analysis is often difficult, particularly when blood clots are present, because many of the amniotic fluid cells may become trapped within the clot. The combined use of trypsin to break up the clot and of ficoll-based lymphocyte separation medium (LSM) was found to be satisfactory for separating red cells from amniotic fluid cells. The procedure was as follows. Any clots present in the specimen of amniotic fluid were trypsinised at 370C for 30 to 40 minutes using a trypsin-versene solution (0 025% lyophilised trypsin, 0.025% EDTA disodium salt in phosphate buffered saline). Four types of culture were set up from each sample of amniotic fluid containing clots: (1) aliquots of untreated blood stained amniotic fluid; (2) aliquots of amniotic fluid treated with LSM to remove the majority of red cells (see below); (3) aliquots of trypsin cell suspension from the trypsinised clots; and (4) aliquots of the trypsin cell suspension which had also been subjected to LMS separation. Standard methods of culture maintenance and harvesting for chromosome preparations were used.'