From the Guidelines
Transferring multiple embryos during IVF can increase the chances of having twins, but it is not a recommended approach due to the associated risks of multiple pregnancies, such as premature birth, low birth weight, and pregnancy complications, as highlighted in the ESHRE guideline 1. The most common way to have twins through IVF is by transferring multiple embryos during the procedure. However, many fertility specialists now recommend single embryo transfer (SET) to reduce the risks associated with multiple pregnancies.
Key Considerations
- The ESHRE guideline 1 emphasizes the importance of considering various factors, including patient age, medical history, and embryo quality, when deciding on the number of embryos to transfer.
- The guideline also highlights the increased risk of ectopic pregnancy, neonatal death, and complications associated with double embryo transfer (DET) 1.
- Even with single embryo transfer, identical twins can still occur if the embryo spontaneously splits after transfer, though this happens in only about 1-2% of IVF pregnancies.
Recommendations
- Elective single embryo transfer (eSET) is considered the preferable approach towards safe and effective ART, as recommended by several international and national professional organizations 1.
- Patients who strongly desire twins should discuss transferring two embryos with their doctor, but this decision should be made carefully considering their age, medical history, and embryo quality.
- The medications used during IVF stimulation do not directly cause twinning in IVF, as they might in treatments like intrauterine insemination.
Important Factors to Consider
- The number of previously failed treatments has long been recognized as a prognostic factor of poor outcomes, with each unsuccessful ART cycle decreasing the odds of ongoing implantation 1.
- Patients for whom DET is considered should be counseled regarding the chances their treatment will be successful, as well as the short- and long-term medical risks, social, and economic factors, preferably as part of shared decision-making 1.
From the Research
IVF and Twin Selection
- IVF can be used to select twins, but it is not a guaranteed method 2, 3.
- The number of embryos transferred during IVF is a key factor in determining the likelihood of twins 4, 5.
- Transferring a single embryo can reduce the risk of twins, but it may also lower the chances of pregnancy 6, 5.
- Repeated single embryo transfer may be an effective way to achieve pregnancy while minimizing the risk of twins 5.
Factors Influencing Embryo Transfer
- Patient-specific, embryo-specific, and cycle-specific factors can influence the decision to transfer one or two embryos 4, 6.
- Women's age, previous childbirth, and spare embryos to freeze are important factors in deciding the number of embryos to transfer 6.
- Knowledge about the risks of multiple pregnancies is higher in females than in males, but many patients still wish to have two embryos transferred 6.
Guidelines for Embryo Transfer
- Guidelines recommend transferring no more than two embryos in women under 35 years, and no more than three embryos in women between 35-37 years 4.
- Single embryo transfer should be considered in women with excellent prognoses, and in those with high-quality embryos and favorable prognoses 4, 5.
- Elective single embryo transfer can reduce the risk of multiple pregnancies, but it may require repeated cycles to achieve pregnancy 5.