Amnifiltration in the first trimester: feasibility, technical aspects and cytological outcome

An amnifiltration system has been developed which allows collection of cells from the amniotic sac in the first trimester of pregnancy whilst only removing 1 ml of amniotic fluid in total. The cells can be cultured and harvested, using the same methods as early amniocentesis, to enable prenatal diagnosis of fetal karyotype. A range of filters constructed from different materials and of differing pore sizes were examined for their ability to trap and subsequently release a maximum number of amniotic fluid cells. The best filter membrane was found to be a cellulose acetate filter of 0.8 micro m pore size. To achieve the same cytogenetic outcome as a 10 ml amniocentesis, a minimum of 20 ml amniotic fluid must be filtered and recirculated through the system.