EVALUATION OF AMNIOTIC-FLUID CELL FILTRATION - AN EXPERIMENTAL APPROACH TO EARLY AMNIOCENTESIS

Prior to a prospective application of amniotic fluid (AF) cell filtrat ion to early amniocentesis, we tested the technique on a surplus from mid-trimester samples. By using the same sample size of 5 ml in experi ments with a filter and in routine diagnostic procedures (control), we evaluated an optimal filter system. The prolonged culture time of fil tered cells and the reduced number of clones are most probably due to mechanical stress (filtration pressure), whereas loss of the cells by adhesion to the filter system, and an AF-free culture medium (growth f actors) are suggested to be less important. The AF cells are very sens itive to mechanical stress. Slow filtration (less-than-or-equal-to 3 m l AF/min) through filters with a high porosity and the largest possibl e pore size should be preferred. A mixed cellulose ester filter membra ne with a pore size of 5.0 mum proved to be the most efficient, allowi ng harvest of the filtered cells after only a slight prolongation of t he culture time (+ 2.4 days) compared with unfiltered aliquots. A filt er set with a bypass connected by three-way taps allows cell filtratio n during either aspiration or reinjection of the AF. Cell filtration a fter amniocentesis and consecutive reverse flushing of the membrane wi th the appropriate amount of culture medium proved to be the best with regard to easy handling and reducing the risk of bacterial contaminat ion.