Let's start by understanding the meaning of multiple births. After an IVF cycle, a woman may give birth to more than one baby, even up to 6 or 7. When discussing IVF, one may hear about the chances of having multiple pregnancies. However, is this information true, and what are the numbers?
First, we have to define two important terms for us to understand the mechanism of IVF with embryos.
Monozygotic twins come from the same egg, and the embryo divides just before uterine implantation.
Dizygotic twins come from two fertilized embryos, each from two fertilized eggs.
As for the mechanism of multiple pregnancies, what happens is that during "normal" fertilization, a single egg is fertilized and becomes a single zygote. This zygote will grow into a single embryo.
There are two different ways in which multiple pregnancies can occur.
A single zygote splits into two different embryos that grow into monozygotic siblings, known as identical twins.
One egg is fertilized and develops into dizygotic siblings.
More rarely, there can be a combination of monozygotic and dizygotic siblings.
Until 2010, the simultaneous transfer of more than one embryo was practiced a lot. This usually resulted in multiple births (30 to 35% of the cases), 30% of whom were twins and 5% triplets.
Today, the average percentage of multiple births is only 4%, and triplet pregnancies are almost nonexistent. This is because, for each IVF, only one embryo is transferred at a time.
The average chance of having multiple births is usually higher with intrauterine insemination. This higher number is due to the use of ovulatory agents during this technique, meaning that the twins from this technique are typically dizygotic.
In addition, superovulation, which consists of hormonal treatment to promote the recruitment and development of several follicles to the preovulatory stage, can induce a higher rate of multiple births that can go up from 8 to 20%.
A higher risk concerning multiple births after an IVF treatment is explained by the fact that during a cycle of IVF, multiple embryos are used to have the best chance of conceiving. Usually, only one of the embryos transforms into a fetus and then a baby. But since there are more embryos than during a natural cycle, women undergoing IVF treatments are more likely to be pregnant with more than one baby than women who undergo natural pregnancies.
However, you don't need to worry about automatically having twins or triplets! The chances of having multiple pregnancies are pretty low, especially concerning more than two babies.
At Unica, we are here to answer all your questions and make your doubts disappear. Don't hesitate to join us on the journey of having your baby!
