The present preimplantation diagnosis test is able to screen for the most common aneuploidies from single blastomeres in about five hours with a 15 per cent misdiagnosis. This means that the risk of spontaneous abortion and trisomic offspring for women of advanced maternal age could be reduced to the same level as younger women for whom prenatal diagnosis is usually not necessary. Better probes and more fluorochromes could improve the success rate of the test.