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Under natural circumstances, the probability of giving birth to twins is approximately 1 in 80–90 cases (around 1.1–1.5%). However, with the development of assisted reproductive technologies (ART), this figure has risen significantly. Multiple pregnancies following IVF are often regarded as a success, but modern medicine views them as a complication due to the increased risks for both mother and babies. Below, we will examine how the chances of having twins vary depending on the chosen protocol.
* This is a collaborative post
Why are twins born following IVF?
The main reason for the high incidence of multiple pregnancies in the past was the practice of transferring two or more embryos into the uterine cavity to increase the overall chances of the procedure’s success. If both take hold, dizygotic (fraternal) twins are born.
There is also a small chance (around 1.5–3%) that a single transferred embryo will split into two, resulting in the birth of monozygotic (identical) twins. This occurs slightly more frequently with IVF than in nature.
1. Standard IVF (own eggs)
In the classic IVF protocol, the chances of having twins depend directly on the woman’s age and the number of embryos transferred.
- When transferring 2 embryos: The chance of a multiple pregnancy is between 20% and 30%.
- When transferring 1 embryo (SET – Single Embryo Transfer): The chance drops to 1–2% (solely due to random embryo division).
The effect of age: In women under 35, the likelihood of both embryos implanting is significantly higher. After the age of 40, the ovaries produce fewer high-quality eggs, and even when two embryos are transferred, the likelihood of twins decreases due to natural genetic factors.
2. IVF with egg donation
In protocols using donor oocytes, the chances of a multiple pregnancy are maximum.
- Why the chances are higher: Donors are young (under 30) and healthy women with a high ovarian reserve. Their eggs have a high potential for implantation.
- Probability of twins: If a patient (regardless of her own age) decides to transfer two embryos obtained from a donor, the chance of giving birth to twins can reach 35–45%.
For this reason, many leading clinics worldwide strongly recommend transferring only one embryo when using donor material.
3. IVF with dual donation (eggs + sperm)
Dual donation involves the use of biomaterial from two young, vetted donors. This creates ‘ideal’ conditions for obtaining embryos of the highest quality (Grade A).
- Chances of twins: Similar to or slightly higher than with standard egg donation. When two embryos are transferred, the probability of twins remains consistently at 40% or higher.
- Key feature: As male infertility or age-related factors in both parents are eliminated in this scenario, embryo survival rates are extremely high. The risk of unplanned twins is highest here.
Summary table of probabilities (when transferring 2 embryos)
Protocol Approximate probability of twins Note
Standard IVF (<35 years) 25–30% Depends on the quality of her own oocytes
Standard IVF (>40 years) 5–10% Low probability of both implanting
Egg donation 35–45% High biological potential
Double donation 40–50% Maximum possible chance
FAQ: Frequently Asked Questions
Is it possible to specifically ‘order’ twins during IVF?
Although transferring two embryos technically increases the chances, fertility specialists do not recommend doing this specifically. A twin pregnancy carries risks of premature birth, pre-eclampsia and low birth weight in the babies.
If a single embryo is transferred, can twins result?
Yes. As mentioned above, in 1.5–3% of cases, a single embryo may split at the blastocyst stage. In this case, monozygotic (identical) twins will be born.
Does ICSI increase the chance of twins?
Statistically, the method of fertilisation (IVF or ICSI) has virtually no effect on the chance of having fraternal twins, but some studies suggest a slightly higher risk of embryo splitting (monozygosity) following manipulation of the egg’s outer layer.
Does cryopreservation (freezing) help to avoid twins?
Freezing does not affect ‘multiple pregnancy’ in itself, but it allows doctors to confidently recommend transferring only one embryo per cycle, knowing that the remaining high-quality embryos will be preserved for future attempts.
Does the chance of twins depend on the day of transfer?
Embryo transfer on day 5 (blastocyst stage) has a higher chance of implantation than on day 3. Consequently, if two blastocysts are transferred, the probability of twins will be higher than when transferring two ‘day-3’ embryos.
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