In vitro fertilization (IVF) and artificial insemination (AI), the main assisted reproductive techniques, are associated with an increased likelihood of pregnancy with twins (non-identical twins) or more babies.
Although these fertility treatments may increase the likelihood of a double pregnancy, there are many current studies aimed at reducing any multiple pregnancies. The main reason for this is the high risk to both maternal health and the development of babies.
For this reason, more and more fertility specialists are recommending that patients transfer a single embryo. This has helped to reduce the rate of multiple pregnancy in the field of assisted reproduction.
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Twins or twins?
It is important to note that, in the case of a double pregnancy after IVF, it is usually a case of twins or twins with twins and not monozygotic twins or identical twins. Below, we explain the difference between the two:
- Twins or bicigotic twins: they come from two different eggs and two different sperm, that is, from different embryos that have developed in the same pregnancy. Twins do not necessarily have to have the same sex or physical characteristics. Therefore, they would simply be two siblings who are the same age.
- Identical twins: they come from the same embryo that, during the first rounds of cell division, has fragmented into two parts giving rise to two identical embryos. Therefore, they contain the same genetic information, which means that they are necessarily of the same sex and very similar physically.
Whether twins or identical twins, pregnancies in which two fetuses develop simultaneously are called twins.
Natural Multiple Pregnancy
For a multiple pregnancy to occur naturally, the following factors must be involved:
- Maternal age
- the older the mother, the higher the probability of having twins. This is due to the increased release of FSH hormone, a hormone that promotes the release of one (or more) egg each cycle. From the age of 33 onwards, the release of this hormone is greater, thereby increasing the chances of ovulation of more than one egg and, therefore, the rate of twin pregnancy.
- Family Inheritance
- there is a greater chance of having a multiple pregnancy if there have been multiple pregnancies in the family history, especially on the mother's side.
- Race and geographic area
- there is a higher incidence of twins in blacks, followed by Caucasians, Hispanics and Asians.
- Maternal weight
- a Body Mass Index (BMI) of 30 or higher means that a woman has a tendency to release more than one egg at each ovulation, so there is a greater chance of having twins.
- The diet
- inadequate nutrition is associated with a lower rate of twin gestation, while women who eat properly and take folic acid supplements have a higher rate.
On the other hand, those women who have had twins before, double the chances of conceiving two babies again. In addition, in women who are not having their first pregnancy, they also have a high chance of a multiple pregnancy.
In any case, either by family tendency or by assisted reproduction, the most common is that the pregnancy is dizygotic. However, cases of identical twins can occur in either case.
Assisted procreation, as any other medical treatment, requires that you rely on the professionalism of the doctors and staff of the clinic you choose. Obviously, each clinic is different. Get now your Fertility Report, which will select several clinics for you out of the pool of clinics that meet our strict quality criteria. Moreover, it will offer you a comparison between the fees and conditions each clinic offers in order for you to make a well informed choice.
Probability of twin pregnancy and twin pregnancy
The probability of having twins in a natural pregnancy is approximately 1.1%, while the percentage of having identical twins naturally is 0.4%.
In contrast, the rates of twin births (both twins and twins) with own eggs in assisted reproduction are 8.7% for each transfer in IVF and 8.2% with artificial insemination. These data have been extracted from the latest statistical report of the Spanish Fertility Society (SEF) corresponding to the year 2021.
As can be seen, twin pregnancy and delivery rates increase considerably when assisted reproductive techniques are used. There are two main reasons for this:
- The transfer of two or three embryos in IVF.
- Stimulation of ovulation so that more than one egg matures in AI.
In both cases, there is the possibility of implanting more than one embryo, so a twin pregnancy could occur. The goal is to increase the chance of pregnancy, but this also increases the chance of multiple pregnancy (pregnancy with two or more babies).
However, the increasingly common trend in assisted reproduction is to transfer a single embryo. In addition, ovarian stimulation for AI is perfectly controlled to avoid a possible multiple pregnancy.
Single or multiple embryo transfer?
In vitro fertilization (IVF) is an assisted reproductive technique in which a woman is given hormone medication to stimulate ovarian production. In this way, the development and maturation of more than one egg is achieved and, therefore, a greater number of embryos will be obtained by recovering a greater number of eggs in the follicular puncture.
After the culture of the embryos, the embryos with the highest implantation potential, that is to say, those of the highest quality, will be transferred. This embryo transfer can be done on either day 3 or day 5, depending on the patient's needs and the possibilities of the reproductive center.
The Spanish law on assisted human reproduction techniques (law 14/2006) allows the transfer of up to three embryos.
The decision of the number of embryos to transfer will be made by the patient or couple, but always taking into account the medical recommendation. The goal is to achieve pregnancy, but without forgetting the risks associated with multiple gestation. In this sense, Dr. Gorka Barrenetxea is clear:
what increases the risk of multiple pregnancy is not a stimulation protocol with GnRH antagonists or agonists, but the number of embryos transferred. In short, what prevents multiple pregnancy in assisted reproduction is the transfer of an embryo. That is why today almost all assisted reproduction centers try to transfer an embryo.
Therefore, more and more specialists recommend the transfer of a single embryo. Thanks to the improvement of embryo selection methods, it is possible to have a very good chance of pregnancy with only one embryo, thus reducing the probability of twin pregnancy.
Probability of twin pregnancy in IVF
According to data collected from 22 European countries by the European Society of Human Reproduction and Embryology (ESHRE), after IVF or ICSI 73.6% of pregnancies are singleton pregnancies (singleton pregnancies), while 24.4% are twins.
On the other hand, according to the 2021 statistical report of the Spanish Fertility Society (SEF), the rate of twin births with own eggs per transfer in Spain stands at 8.7% this year. However, in previous years this percentage was higher. For example, the twin birth rate in 2000 was 28.7%.
Therefore, the strategies followed by reproductive health professionals are decreasing the rates of twin pregnancy, as well as the risks associated with it.
Probability of identical twins
Although the majority of multiple pregnancies resulting from in vitro fertilization are twins (dizygotic twins), there also seems to be a greater tendency for twin pregnancies (monozygotic twins).
It is estimated that there is an increase of approximately 1.5-2% of monozygotic twin pregnancies. This means that even by transferring a single embryo there would be a small chance of a twin pregnancy in IVF.
It is not known exactly why this increase occurs, although there are different hypotheses about the mechanisms that may explain it. The zona pellucida of the embryo seems to play an important role, since for the embryo to implant in the uterus it is essential that it comes out of this envelope once it has reached the blastocyst stage.
In general, the embryo comes out without problems thanks to the mechanical and enzymatic action exerted on it. Under certain circumstances, the embryo may split in two as it emerges from the zona pellucida. This may be induced by the following factors:
- Manipulation of the zona pellucida in ICSI (intracytoplasmic sperm injection), which can be used as an alternative to conventional IVF to fertilize eggs.
- Assisted hatching, which consists of making a hole in the zona pellucida to facilitate the exit of the embryo for its subsequent implantation.
- The hardening of the zona pellucida caused by ovarian stimulation.
- The development of the embryo in culture media under conditions of in vitro.
In any case, the probability of this happening is quite low. As a result, more and more IVF pregnancies are ending with a single healthy baby at home.
If you want to know more in depth information about IVF success and read about other statistics, you can visit this article: What Are the Average IVF Outcomes by Age?
Probability of twin pregnancy by AI
In artificial insemination (AI) there is also a previous step of ovarian stimulation, but in a much gentler way than in the case of IVF. This difference lies in the fact that AI is only intended to achieve the development of 1-2 ovarian follicles. Otherwise, if there is a major development, the AI will be cancelled.
Therefore, low doses of hormonal medication are used in an AI treatment. This allows greater control of the exact time of ovulation and follicular growth. When the follicles have reached the desired size, the patient will be given medication to induce ovulation and the insemination will be scheduled.
According to the 2021 statistical report of the Spanish Fertility Society (SEF), the percentage of twin birth with AI is 8.2%; while the singleton birth rate is 91.5%. In addition, these results vary depending on whether it is an AI with conjugal sperm or donor sperm at 7.9% and 8.5% respectively.
FAQs from users
Is it more likely to have twins by artificial insemination or in vitro fertilization?
Spontaneous twin pregnancy occurs in approximately 1-2 out of every 100 pregnancies. In recent decades in developed countries, the rate of twin pregnancy has increased to 3-4% due to multiple causes such as the increase in maternal age, the increase in assisted reproductive techniques, etc.
Reproductive treatments substantially increase the prevalence of twin pregnancy in our population, compared to natural conception.
Within twin gestation we can differentiate two large groups: monozygotic twins (fertilization of a single oocyte by one sperm, which divides after fertilization) and dizygotic twins (fertilization of two oocytes by two sperm).
Dizygotic twins are more common in IVF cycle gestations than in spontaneous conditions because some patients receive a double embryo transfer. IVF increases the percentage of embryo division and is also responsible for an increase in the number of monozygotic twins.
As for cycles without IVF, with ovulation inducers and artificial insemination, they also increase the percentage of dizygotic twin pregnancies because of the possibility of multiple ovulation and fertilization. This possibility can be diminished by being selective when performing our insemination protocols, trying to prioritize monofollicular development in the AI cycle.
How can I get pregnant with male twins through in vitro fertilisation?
There is no way to increase the likelihood of identical twins or to ensure that you will have two babies. However, it is possible to increase the chance of having twins by transferring two embryos. It is important to keep in mind that the risks are increased in this type of pregnancy, as there is a greater likelihood of maternal and foetal complications.
To choose the sex of the embryos, pre-implantation genetic diagnosis (PGD) would be necessary, but in Spain sex selection is only allowed for therapeutic purposes.
Can I choose to have twins in my fertility treatment?
You can choose to transfer two embryos instead of one to increase the likelihood of pregnancy and thus increase the likelihood of a twin pregnancy. However, there is no way to ensure that both will implant.
What is the probability of having twins in DAI?
According to the latest statistical registry of the Spanish Fertility Society (SEF) for 2021, the rate of twin births in AI with donor sperm is 8.5% compared to the 91.2% chance of a single birth. The remaining 0.3% corresponds to triple births.
Is a multiple pregnancy of twins more risky because of in vitro fertilisation or artificial insemination?
In principle, there is no increased risk because the pregnancy is achieved through assisted reproduction. Multiple pregnancy itself is considered high-risk, whether it is achieved naturally or not. In the mother, pathologies such as gestational diabetes, hypertension or pre-eclampsia may appear in a higher proportion.
In the baby, there may be prematurity and low birth weight. This means that organs such as the lungs are not mature and, therefore, the probability of survival is reduced.
How does twin pregnancy occur in AI?
In order for a twin pregnancy to occur by inseminating a woman, it is necessary that two eggs are expelled at ovulation. In addition, it is essential that both eggs are fertilised, that the two embryos generated develop to blastocyst and that they manage to implant in the patient's uterus.
In contrast, for a twin pregnancy, the embryo resulting from the fertilisation of one egg must be divided into two. In artificial insemination, the fact that the embryo fragments during its development does not seem to be increased, so the probability of identical twins can be considered the same as naturally.
What are my chances of having twins with ICSI?
No, it basically depends on the number of embryos to transfer. The chances of having a multiple pregnancy with single embryo transfers (SET) are very low. However, with two embryos, it rises to 6%.
Suggested for you
If you are interested in learning more information about the general IVF process, we recommend you read the following article: The IVF Process - How Is It Done Step by Step?
However, if you would like to continue reading about the possible risks of a multiple pregnancy, don't forget to visit this link: Potential Complications of Multiple Pregnancies.
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References
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FAQs from users: 'Is it more likely to have twins by artificial insemination or in vitro fertilization?', 'How can I get pregnant with male twins through in vitro fertilisation?', 'Can I choose to have twins in my fertility treatment?', 'What is the probability of having twins in DAI?', 'Is a multiple pregnancy of twins more risky because of in vitro fertilisation or artificial insemination?', 'How does twin pregnancy occur in AI?' and 'What are my chances of having twins with ICSI?'.
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