We have to admit that monozygotic twins are pretty interesting. They come to life because sometimes a fertilized egg divides into two embryos within 2 weeks after conception. According to the moment when the division takes pace, each zygote could have its own placenta or membranes.
Types of placenta and identical twins
Two placentas and two amnios
If the fertilized egg gets divided into two embryos within 72 hours of conception, the two babies will develop in separate amniotic sacs and also they will have their own placentas. Nonetheless the findings of the studies show that the separate placentas could fuse at some point in the development of the pregnancy.
One placenta and two amnios
The twins that are identical could come to life as a result of the division of the fertilized egg after 3-8 days of conception. In this case the babies will have their own amniotic sacs but they will have the same placenta. This is similar to the case when the two placentas fuse.
One placenta and one amniotic sac case 1
The truth is that such monozygotic twins are quite rare. The babies will have the same placenta and amniotic sac if the fertilized egg gets divided 8-12 days after conception. Women have twins of this kind only in 1%-2% of all cases.
One placenta and one amniotic sac case 2
You might think that the identical twins are something like in the previous case. The truth is that this is a really rare case. If the division takes place during the 12th-13th day after conception the babies will have the same amniotic sac and placenta and they will also share some of their body parts.
Findings of the ultrasounds
When it comes to monozygotic twins it is quite possible that the doctors miss the signs on the ultrasound. This means that at the beginning the doctors may think that there is only one baby. The ultrasound images show a single placental site, fetuses of the same sex and thin dividing membrane.
Factors
There are some factors that make the appearance of twins that are identical more likely. The chances of having twins of this kind are of 3-5 in every 1,000 births. It looks like the chances are higher to have twins if the mother used ovulation induction techniques             .
In the same time the appearance of the monozygotic twins also depends on the number of blastocysts that were transferred into the uterus if the mother used IVF or in vitro fertilization. The family history of the parents of having twins is also an influencing factor.
It is believed that it is more likely to have geminates if the mother or the father has a twin sibling or has someone in the family who has twins. However, if you have a twin sibling that doesn’t mean that you will have twins as well.
Now you know a lot more about monozygotic twins and you should also know that, contrary to the common belief, the genes of the babies aren’t the same.
