[Trisomy 20 mosaicism in amniotic cell culture. Genetic counselling during the prenatal diagnosis].

The author presents a new case of trisomy 20 mosaicism in an amniotic fluid culture and emphasizes the special aspects of this chromosomal abnormality. The prenatal diagnosis of "pseudo-mosaicism" is easier when in situ culture techniques are used. Controls of the results on a new sample of amniotic fluid and/or on foetal blood are useful to reinforce the diagnosis and to allow pregnancy to be continued.