In 37 pregnancies with placental mosaicism detected at first-trimester chorionic villus sampling in 2000 pregnancies, two pregnancies (5.4 per cent) ended in a spontaneous abortion at 15 weeks (46,XX 47,XX, + 16) and in a perinatal loss in a term pregnancy (46,XY/47,XY, + 10), respectively. The outcome of the other 35 pregnancies was normal. The total pregnancy loss rate before 28 weeks in the first 1000 pregnancies was previously reported to be 3.6 per cent.