Outcome of pregnancies with trisomy 2 cells in chorionic villi.

OBJECTIVE To describe the outcome of pregnancies with trisomy 2 in cultures of first-trimester chorionic villous samples (CVS) and determine whether amniocentesis is necessary in the management of such cases. METHODS Cultures of chorionic villi were performed at 11-13 weeks in 37 474 pregnancies. In those with trisomy 2 cells, amniocentesis was performed at 16 weeks. Pregnancy outcome was obtained from maternity records. RESULTS Trisomy 2 cells in CVS cultures were observed in 45 of 37 474 pregnancies (1.2 per 1000). In 43 cases ultrasound examination at 16-20 weeks showed no fetal abnormalities, amniocentesis demonstrated the presence of only normal cells, and all 43 pregnancies ended in normal healthy live births. The birth weight was below the 5th centile in six neonates (13.9%). There was a significant association between the birth weight centile and the percentage of trisomic cells in the CVS culture (r = 0.409, p = 0.010). In one case, there was fetal death at 15 weeks. In a second case, amniocentesis showed one cell with trisomy 2 in a total of 53 cells, and ultrasound examination at 18 weeks showed severe fetal growth restriction and coarctation of the aorta. CONCLUSION In at least 95% of cases with trisomy 2 in CVS cultures there is confined placental mosaicism (CPM). The prognosis is good, but in about 15% of cases there is fetal growth restriction.