A sample of amniotic fluid containing cells may be taken out from the amniotic cavity by penetrating the wall of the amniotic cavity by means of a hollow needle (15) through which a volume of the amniotic fluid may be withdrawn. Outside the amniotic cavity the cells or part thereof are separated from the amniotic fluid which is immediately thereafter returned to the amniotic cavity. This means that it is possible to withdraw a relatively large amount of cells without considerably reducing the total volume of the amniotic fluid present in the amniotic cavity. Therefore, it is possible to take out a sample at an early stage of the pregnancy period. The sample may, for example, be withdrawn by means of a sampling device comprising a one-way valve (16, 17) including a cell filter (17). The sampling device may further comprise a syringe with cylinder (10) and a piston (11) movably arranged therein. By moving the piston (11) through a suitable number of consecutive suction and pressure strokes a suitable amount of cell material is deposited on the cell filter (17). The filter (17) may be withdrawn from the sampling device and the cells may be cultured on the cell filter or the cells may be flushed from the filter by means of a culturing medium.