THE HIDDEN MORTALITY OF MONOCHORIONIC TWIN PREGNANCIES

In an ultrasound screening study at 10 to 14 weeks of gestation for me asurement of fetal nuchal translucency thickness there were 102 monoch orionic and 365 dichorionic twin pregnancies. In the monochorionic com pared with the dichorionic pregnancies there was a higher rate of feta l loss before 24 weeks of gestation (12.2% versus 1.8%), perinatal mor tality (2.8% versus 1.6%), prevalence of delivery before 32 weeks (9.2 % versus 5.5%), and prevalence of birthweight below the 5th centile in both twins (7.5% versus 1.7%). However, the proportion of pregnancies with a birthweight discordancy of more than 25% was similar in the tw o groups (11.3% versus 12.1%).