Is zygosity or chorionicity the main determinant of fetal outcome in twin pregnancies?

Objective: The purpose of this study was to examine whether fetal outcome in twin pregnancies is dependent on zygosity or chorionicity.

Study Design: This was a prospective observational study comprised of women with twin pregnancies who attended the fetal medicine unit at St Michael's Hospital, Bristol, Ireland, during the years 1998 to 2000 and who were delivered in hospitals in south west England. After delivery, zygosity was determined with umbilical cord blood with the use of microsatellite markers that were amplified by polymerase chain reaction.