Filtration and recirculation of early amniotic fluid. Evaluation of cell cultures from 100 diagnostic cases.

Due to the low cell concentration, cultures from early amniotic fluid specimens usually require 2-3 weeks in culture prior to karyotyping. The purpose of this study was to evaluate the culture quality of amniotic fluid cells from early pregnancy, obtained by a new filter technique. The hypothetical advantage of the technique was that the increased cell yield might reduce the culture time before karyotyping. Culture quality was assessed by the number of colonies, the percentage of colonies containing mitoses in filter and control cultures, and the culture time. The setting was a consecutive clinical trial. One hundred samples were obtained from ongoing pregnancies at 11-14 weeks of gestation (mean 12.8 weeks). By circulating a mean of 26 ml of amniotic fluid through a cell filter system leading the cell-free fluid back to the amniotic cavity, the cell yield was increased in the sample of 7 ml corresponding to the dead space of the filter system. The culture results were compared with control cultures from 5 ml samples drawn from the same pregnancies prior to recirculation. The cultures from the first flushing of the filter system yielded 2.6 times more colonies and in total 4.2 times more colonies were found in the three cultures grown from each filter sample when compared with the control cultures. Moreover, the filter cultures showed significantly more colonies with mitoses. The mean culture time was 8.0 days for the filter cultures, from which the karyotypes were analysed. The controls would have needed more time in culture to fulfil the diagnostic criteria for karyotyping. One case of 47,XY,+21 was found; the rest had normal karyotypes. We conclude that the filter technique improves the culture quality of early amniotic fluid samples and allows early arrest of the cultures.