Monochorionic diamniotic conjoined twins

Monochorionic diamniotic (MCDA) conjoined twins are extremely rare. In monochorionic monoamniotic (MCMA) conjoined twins, the embryonic disc failed to undergo complete separation at 15-17 th day of gestation. Conversely, MCDA conjoined twins occur when two originally separate monovular embryonic discs undergo secondary infusion. Literature review shows four reported cases. Two cases were detected in the first trimester and terminated. The third case detected at 14 weeks was a triplet pregnancy, but unfortunately miscarried after a fetal reduction procedure. The fourth case reported was detected only at 31 weeks, and delivered at 35 weeks, with the fetuses joined at the umbilicus separated successfully. We report the 5 th case. Patient E was in her third pregnancy having had two normal deliveries previously. Her current pregnancy was booked at 12 weeks, and ultrasound at this gestation confirmed MCDA twins, with no suspicion of the fetuses being conjoined. At 19 weeks9 scan, a connection (24mm x 29mm) above the level of the male fetuses9 bladders was noted at the lower abdomen. The scrotums appeared bifid, and the bladders appeared small on ultrasound. Patient E made an uneventful progress to term and delivered the conjoined fetuses by a classical caesarean section. Bowels were noted in the connecting bridge and successfully separated after birth. Accurate prenatal diagnosis is challenging in MCDA twins, but important for parental counselling by paediatric surgeons. Management from diagnosis to delivery and twin separation requires a multidisciplinary input involving fetal medicine specialists, obstetricians, neonatologists and paediatric surgeons.