Placental Characteristics of Monoamniotic Twin Pregnancies in Relation to Perinatal Outcome

OBJECTIVE: To study placental characteristics in relation to perinatal outcome in 55 pairs of monochorionic monoamniotic (MA) twins. METHODS: Between January 1998 and May 2008 55 pairs of MA twins were delivered in 4 tertiary care centers and analysed for mortality, birth weight discordancy and twin-to-twin transfusion syndrome (TTTS) in relation to type of anastomoses, type and distance between cord insertions and placental sharing. Five acardiac twins, 2 conjoined twins, 4 higher order multiples and one early termination of pregnancy were excluded, leaving 43 MA placentas for analysis. Of these 43, one placenta could not be analysed for placental vascular anastomoses due to severe maceration after single intra-uterine demise leaving 42 placentas for analysis of anastomoses. RESULTS: Arterio-arterial (AA), venovenous (VV) and arteriovenous (AV) anastomoses were detected in 98%, 43% and 91% of MA placentas, respectively. Velamentous cord insertion was found in 4% of cases. Small distance between both umbilical cord insertions (