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Conjoined twins are born attached at the chest. Examination of the placenta would likely reveal which of the following arrangements of the fetal membranes?


b.-Diamnionic, fused dichorionic

c.-Diamnionic, monochorionic

d.-Monoamnionic ,dichorionic

e.-Monoamnionic, monochorionic


e.-Monoamnionic, monochorionic ??

As i see it is like this

Dizygotic twins/ Faternal twins = 2 separate aminions and placentas. Everything different as 2 separate sperms fertilize 2 separate ova.

Monozygotic twins = A single FERTILIZED OVUM SPLITS into 2 during the following 2 weeks of conception.

Split @ days 5-6 (cleavage of blastomere) will have two complete sacks, both amnionic and chorionic. 30% of monozygotic twins are like this.

Split @ days 6-11 (cleavage of inner cell mass) will have separate amnionic sacks but will be within the same chorionic sack. The membrane separation (amnionic) will be very thin. Around 70% of the monozygotic twins are like this

Split @ day 12 will have same chorionic and amnionic sack. 1 out of every 100 monozygotic twins is in the same sack.

Split @ day 14 causes incomplete division, conjoined twins.

Split @ day 16 causes parasitic twinning. Can have, for example, extra limbs or pelvis.

Split after day 16 can causes teratoma.

Had this info written down somewhere in my old embryo notes had to find this one. Hope this helps.


It's E.


E. Conjoined twins/Siamese twins----monochorionic,monoamniotic placenta(due to incomplete splitting of the embryo)

Good explanation n_n_l


Logically if the twins are conjoined, there must be monochorionic and monoamnionic.

Maybe attached image could be help.


Thanks, guys. explanation and images are great

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