If division of feilized egg takes place in between 5-8 days. It would give rise to which kind of twin pregnancy: March 2009, March 2013 (c)

Ans. B: Monochorionic/diamniotic Approximately 70% of monozygotic twins are monochorionic /diamniotic. If splitting occurs later (ie, 9-12 d after feilization), monochorionic/ monoamniotic placentation occurs. Monochorionic/monoamniotic twins are rare; only 1% of monozygotic twins have this form of placentation. twins have a common placenta, with vascular communications between the 2 circulations. These twins can develop twin-to-twin transfusion syndrome (TTTS). If twinning occurs more than 12 days after feilization, then the monozygotic feilized ovum only paially splits resulting in conjoined twins.