OC01.04: Perinatal Outcome after First Trimester Risk Assessment in Monochorionic and Dichorionic Twin Pregnancies: a Danish National Database Study

To evaluate the influence of chorionicity on outcome in twin pregnancies, using a Danish national database including women having first trimester ultrasound and risk assessment. A cohort of 3,372 dichorionic twin (DC) pregnancies and 638 monochorionic twin (MC) pregnancies (608 diamniotic, MCDA, and 30 monoamniotic, MCMA) from the period July 2008–July 2011 was collected from the Danish national fetal medicine database. The database includes more than 97% of women having first trimester risk assessment in Denmark. Primary outcomes were fetal loss rate before week 22, intrauterine death rate from week 22 to birth, and neonatal mortality. Secondary outcomes were chromosomal trisomy, and rate of termination or selective fetocide. Outcome data was available in 97.1% of all twin pregnancies. In 98.3% of DC pregnancies, 90.7% of MCDA pregnancies and 56.7% of MCMA pregnancies at least one live infant was born. The rate of spontaneous loss of at least one fetus before gestational week 22 was 3.6% in both DC and MCDA pregnancies, and 30.0% in MCMA pregnancies. After week 21 + 6 the rate of spontaneous loss of at least one fetus was 0.6% in DC pregnancies, 2.6% in MC pregnancies (P < 0.005). The neonatal mortality rate was similar (1.0%) in DC and MC pregnancies. Prenatal karyotyping showed 15 DC fetuses and 2 MC fetuses with Down's syndrome. 13 DC infants had a postnatally diagnosed chromosome anomaly, and were all screen-negative. Termination or selective fetocide was performed in 1.7% of the DC and in 6.8% of the MCDA pregnancies (P < 0.005). MCDA and DC twins have comparable risks of spontaneous loss before week 22 as well as neonatal death in our study group, whereas the risk of spontaneous loss between week 22 and delivery as well as termination is higher in MCDA pregnancies.