Question for Embryologist on twins
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This question is for doctor.
I am having a difficult time understanding the diagnosis of identical diamniotic-dichorionic twins compared to fraternal twins.
If I understand correctly, di/di twins are identical twins that split within 3-4 days of fertilization, before the embryo reaches blastocyst stage. They go on to have their own chorion and amniotic sacs during gestation.
A discussion on another forums says that these "di/di" twins still begin inutero in the same gestational sac even though they have divided prior to implantation. That in early u/s, this is how fraternal twins can be distinguished from "di/di" twins. All types of identical twins including di/di originally beginning in one gestational sac, and all fraternal twins in two sacs.
This is where I am confused. If the divide occurs prior to blastocyst stage, how do the embryos come to share the same gestational sac? Wouldn't they be traveling around the uterus/tubes as two distinct embryos once the split is made and before the burrowing process of implantation begins? Or is there some sort of adhesion that binds them until a later date into the pregnancy at which point they do have their own placenta and sac?
I would really appreciate clarification on this topic as I am having trouble grasping how/why the di/di identicals would *always* be in the same gestational sac given the early division.
Thank you for your input!
Kindredly~
Lizzie :D :D[b][/b][b][/b]
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