following pictures and text explain the difference between identical and
Twins (also known as Uniovular or Monozygotic twins).
During the fertilization
process, only one ovum is impregnated by only one spermatozoid, but the egg divides in 2
embryos afterwards. They have exactly the same chromosomes, they
have a perfect resemblance and they have the same sex.
There are 3 different
ways that identical
twins can develop and be carried:
the first case there is only
one placenta that feeds the babies, but there can be two amniotic sacs
(as in the diagram at the side). When there is 1 placenta and 2
amniotic sacs then the pregnancy is referred to as having a "mono-chorial"
placenta and is "bi-amniotic".
In the second scenario,
there is only one
amniotic sac. In the case of 1 placenta and 1 amniotic sac then the
pregnancy is referred to as having a "mono-chorial"
placenta and is "mono-amniotic".
The third scenario is
where there are two placentae and each embryo has its own amniotic pocket.
there are two placentas and two amniotic pockets like this, then one speaks of
a "bi-chorial" pregnancy
that is "bi-amniotic".
(This last case is an identical situation to fraternal twins as shown
Twins (also known as Fraternal, Binovular or Dyzygotic twins).
When twins are non-identical, then two seperate eggs have been impregnated by 2
They each have a different chromosome make-up, they don't look alike
and they can be either the same or different sex. In fact, this is
simply two separate pregnancies that just happened to occur at the same
Each embryo is in its own
amniotic sac and has its own placenta. This type of pregnancy is
referred to as "bi-chorial" and
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