What are the chances to expect twins after an assisted reproduction treatment?
70% of pregnancies in Spain are achieved thanks to assisted reproduction techniques with an outcome of single babies while 30% are multiple pregnancies. In this rate, most of them are twin pregnancies and in just 1% of the cases three eggs are fertilized. According to the Spanish legislation on Assisted reproduction, up to 3 embryos per cycle are allowed to be transferred. Exceeding this number would represent a high risk for the woman and the chances of a multiple pregnancies would be increased. At Eva Clinics, our team supports the transfer of two embryos except in those cases where one more embryo is required to enhance the chance to get pregnant.
The main fertility techniques, In vitro Fertilization (IVF) and Intrauterine Insemination (IUI) are associated with possibility of expecting twins or more babies.
Twin pregnancy: fraternal or identical twins?
Whether they are fraternal or identical twins, a pregnancy where two fetuses develop simultaneously are called multiple pregnancies. In assisted reproduction, twin pregnancies are usually more likely referred to fraternal twins (dizygotic) and not identical twins (monozygotic). What is the difference between fraternal or identical twins?
- Fraternal or dizygotic twins: This occurs when two eggs are developed from two different sperm cells; two different embryos are developed within the same pregnancy. Fraternal twins do not necessarily have the same sex but they are either very similar or just a little as two brothers. They are simply two siblings of the same age.
- Identical twins: It is when one single egg is fertilized by one single sperm cell. During the cell division, the same embryo is split in two identical embryos. Therefore, they share genetic information, sex and a great physical similarity.
Why is there greater chance of having twins following assisted reproduction techniques?
Multiple birth rates are increasing considerably after fertility treatments. On one hand, in IVF procedures from 1 to 3 embryos are transferred (depending on each case) in order to improve the pregnancy success rates. In the Intrauterine Insemination, multiple pregnancies are due to ovarian stimulation which the future mother undergoes in order to obtain more than one mature egg.
According to the statistical report about assisted reproduction techniques from the Spanish Fertility Society, multiple pregnancy rates in IVF (fraternal and identical twins) are about 19, 4% and in Intrauterine Insemination are 10,6%. Nevertheless, in order to avoid multiple pregnancies, the assisted reproduction clinics transfer one embryo, depending on the specific case, and closely monitor the medication’s protocol to obtain one or two embryos. So, thanks to improved methods for embryo selection, it is possible increasing the pregnancy rates by implanting just one embryo and reducing the risk of multiple pregnancies.