Single vs. Double Embryo Transfer: Understanding Success Rates and Twin Risks with Data

In fertility treatment, embryo transfer is a vital step that brings hope to many couples on their TTC journey. During this process, your doctor may present you with the option of transferring either one embryo or two. This decision involves balancing the desire for pregnancy success with the potential risks associated with a twin pregnancy, making it a challenging choice for many. In this article, we'll objectively explain this difficult decision, drawing on the latest evidence and relevant statistics.

Basics of Embryo Transfer: Single Embryo Transfer (SET) vs. Double Embryo Transfer (DET)

Embryo transfer is the process of placing embryos, obtained through in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI), back into the uterus. The number of embryos transferred leads to two main approaches:

Single Embryo Transfer (SET): Only one high-quality embryo is transferred to the uterus. The primary goal of SET is to achieve a singleton pregnancy.
Double Embryo Transfer (DET): Two embryos are transferred to the uterus. This approach is sometimes chosen with the expectation of increasing the pregnancy rate.

Benefits of Single Embryo Transfer (SET) and Why It's Recommended

Global reproductive medicine societies, including those in Japan, recommend Single Embryo Transfer (SET) as the first choice. The primary reason for this recommendation is the safety associated with singleton pregnancies. Singleton pregnancies minimize risks to both the mother and the baby.

Higher Success Rates for Singleton Births: By selecting and transferring a single high-quality embryo, the overall pregnancy rate can be maintained for singleton births while avoiding the risks of multiple pregnancies.
Reduced Maternal Risks: Twin pregnancies significantly increase the risk of complications such as preeclampsia, gestational diabetes, placenta previa, and preterm birth compared to singleton pregnancies.
Reduced Fetal Risks: Twin pregnancies are known to increase the risks of low birth weight, prematurity, and cerebral palsy.

Thanks to advancements in embryo culture and cryopreservation technologies, pregnancy rates with SET are now comparable to, or even surpass, those achieved with DET, but without the increased risks. This has made SET the standard treatment in many clinics. To make the best choice for your situation, proactive preconception care is essential.

When Double Embryo Transfer (DET) May Be Considered and Its Caveats

Double Embryo Transfer (DET) may be chosen in specific circumstances where an improved pregnancy rate is anticipated. These might include cases of advanced maternal age, lower embryo quality, or prior unsuccessful SET cycles.

However, when opting for DET, it is crucial to understand that while it may offer a slightly higher chance of a BFP, it comes with a significantly increased risk of twin pregnancy.

Limited Increase in Pregnancy Rates: DET does not "dramatically" increase pregnancy rates. Especially when good quality embryos are available, the difference in pregnancy rates compared to SET is often small, yet the twin pregnancy rate substantially rises.
Risks Associated with Twin Pregnancy: As mentioned, the risks of twin pregnancy are extensive. These are not merely "the joy of having twins" but can involve significant medical, physical, and emotional burdens for both the parents and the children. From a long-term perspective, avoiding risks like preterm birth is preferable for supporting a child's healthy development.

Your doctor will comprehensively assess your age, medical history, embryo quality, and overall health to determine if DET is appropriate. It's important not to choose DET with the simplistic assumption that "transferring two embryos will definitely result in twins." Your feelings are valid, but making an informed choice is key during your two-week wait (2WW).

Understanding the Trade-off: Success Rates vs. Twin Risks

Let's look at some concrete numbers. Generally, for good quality embryos, pregnancy rates for SET and DET are often similar or show only a marginal difference. However, the incidence of twin pregnancies can jump several to more than ten-fold with DET compared to SET.

For instance, some studies report that while a singleton pregnancy rate with SET using a good quality embryo might be around 40%, DET might increase the overall pregnancy rate to about 50%, but approximately 30% to 40% of these pregnancies would be twin pregnancies. When considering the value of a safe singleton birth, the reasons for recommending SET to avoid high-risk twin pregnancies become much clearer.

It is crucial to take ample time to discuss your specific situation and embryo status with your treating physician. Ensure you fully understand the pros, cons, and specific statistics of each option. This decision can significantly impact your future pregnancy, childbirth, and career plans.

Frequently Asked Questions (FAQ)

Q1: Does transferring two embryos always guarantee a higher chance of pregnancy?

A1: Not necessarily. If you have good quality embryos, SET can achieve a pregnancy rate comparable to DET, but without the significant increase in twin pregnancy risk. The slight potential increase in pregnancy rate with DET needs to be weighed against the increased risks to both mother and babies.

Q2: What are the main risks associated with having twins?

A2: Twin pregnancies carry numerous risks for both the mother and the fetuses, including preterm birth (especially threatened preterm labor), low birth weight, preeclampsia, gestational diabetes, placenta previa, and an increased rate of C-sections. These risks are considerably higher than in singleton pregnancies.

Q3: How should I decide between SET and DET?

A3: The final decision should be made through comprehensive discussion with your reproductive medicine specialist. They will consider your age, embryo quality, past treatment history, health status, and family preferences, providing recommendations based on the latest evidence. Your doctor is your guide to help you navigate this important choice on your TTC journey.

Summary

The choice between Single Embryo Transfer and Double Embryo Transfer is a delicate balance between the desire for pregnancy success and the avoidance of twin pregnancy risks. Advances in reproductive medicine have highlighted the importance of SET for aiming for a singleton pregnancy, though DET may still be considered in specific individual circumstances.

It is crucial to understand your own situation, leverage evidence-based information, and have a thorough discussion with your treating physician until you feel comfortable with your decision. If you have any concerns or questions, do not hesitate to ask, and actively gather information to ensure you make the optimal choice.

References

Japan Society for Reproductive Medicine. Reproductive Medicine Guidelines 2021.
American Society for Reproductive Medicine. Optimizing Natural Fertility. 2022.

Written by the same author — a general guide to preconception care and fertility planning: https://amazon.com/dp/B0F7XTWJ3X?tag=ttcguide-enblog-22