How are identical twins formed?

Predisposition favors twin pregnancies

One in 85 pregnancies is a twin pregnancy. About a third of these are identical twins. The probability of giving birth to identical twins is just 0.4 percent. Whether you will have twins at all depends heavily on whether there are already twins in your maternal family. If this is the case, the probability of a twin pregnancy  increases fivefold. 

Identical and fraternal twins – the differences

Twins can look confusingly alike or have almost no physical similarities. The reason for this lies in the emergence of the twins.

If two mature egg cells migrate into the fallopian tube after ovulation and are fertilized by two sperm cells, dizygotic twins are formed. The genome of the two growing embryos is therefore different. Consequently, fraternal twins can be of different sexes. In principle, fraternal twins are no different from other pairs of siblings.

One egg cell fertilized by one sperm cell is sufficient for the creation of identical twins. If this egg cell divides into two separate cells after fertilization, they each develop into their own child. The DNA of identical twins is therefore identical. It is therefore not possible for identical twins to have different sexes. You get either two boys or two girls. Since the twins share the same genetic makeup, they look confusingly similar.

Identical twins – possible variants of origin

Whether identical twins share the amniotic sac and placenta depends on when the fertilized egg divides.

• If the division takes place within the first few hours after fertilization, this is still happening in the fallopian tube. The two separated eggs then implant themselves in different places in the uterus. Thus, each of the two children has its own placenta and its own amniotic sac.
• If the division occurs between the 4th and 7th day after fertilization, the egg cell is already in the uterus and has implanted itself. The twins then share a placenta and an amniotic sac. However, it may be that each of the children is surrounded by its own membrane.
• If the cell division only takes place between the 8th and 12th day, the twins have to share both the placenta and the amniotic sac and also have a common membrane.

Twin pregnancies are always high-risk pregnancies

The cheapest option is when each child is supplied by its own placenta and has its own amniotic sac. If they have to share both, there is a risk of the so-called twin transfusion syndrome. These are connections of the baby’s bloodstream in the placenta. The result can be an undersupply of one of the children. If the twins also have to share an egg membrane, there is a risk that the umbilical cords will become entangled.

In general, the risk of premature placenta detachment and premature birth is significantly increased in multiple pregnancies. If you are pregnant with twins, your doctor will examine you closely. He will use an ultrasound to check how your children are doing. In addition, he will keep an eye on your blood pressure. In twin pregnancies, the risk of EPH gestosis  is twice as high as in singleton pregnancies.

What to expect when you are pregnant with twins

• Two children in the womb also means more pregnancy hormones that your body releases. Especially in the first trimester of pregnancy, nausea can really get to you.
• Hormone production in twin pregnancies is also running at full speed in the second trimester of pregnancy. The body releases more of the hormone progesterone than with a singleton pregnancy. Unfortunately, this hormone causes increased water retention in the tissue.
• When the children grow up in your belly, things get pretty cramped over time. Your lungs then no longer have as much space to expand in the direction of your stomach. So it may be that you run out of breath quite quickly .
• Pregnant women often have to deal with back problems anyway . With twin pregnancies, the problem is exacerbated for one simple reason: you’re carrying twice the weight in your belly.

Finally, a tip: Build the nest for your twins as early as possible. Take care of the initial equipment and the room furnishings, as long as your stomach is not that big. The closer the birth gets, the less rest you will have. Your twins in the belly have little space and possibly a different sleep rhythm. There will probably be a lot of boxing and kicking.