Short communication: trophoblast proliferation is increased in chorionic villi from pregnancies with fetal trisomy 18.

Pregnancies with fetal trisomy 18 suffer from severe intrauterine growth restriction from the first trimester. This cross-sectional study of chorionic villi obtained from ongoing singleton pregnancies at 10-14 weeks of gestation, semiquantitatively examines chorionic villus stromal and trophoblastic cell proliferation rates in ongoing chromosomally normal and trisomy 18 pregnancies. Chorionic villi were stained using a standard immunohistochemistry protocol with a monoclonal antibody to the Ki-67 antigen and the number of Ki-67 positive trophoblastic and stromal cells per villous cross-section was compared between groups. The number of Ki-67 positive trophoblastic and stromal cells was significantly higher in the group (n=10) with trisomy 18 compared to the chromosomally normal group (n=25;t=2.1, P=0.03 and t=5.3, P<0.001 respectively). Abnormalities in control of cell turnover during development may be important in the pathogenesis of the clinical features of trisomic pregnancies.