Blastocyst Transfer Success Rate: A Guide to Day 5 Embryos and IVF Outcomes

Reviewed By: Dr. Kavya Reddy, fertility specialist at Ferty9 Fertility Center, Visakhapatnam

Blastocyst transfer in IVF is an innovative breakthrough in the field of assisted reproduction. It has various advantages over standard transmission methods. The procedure improves the chances of successful implantation, reduces the risk of multiple pregnancies, and allows for better embryo selection. Blastocyst transfer is a true blessing for couples to fulfill their dream of having a child and starting their family.

What is Blastocyst Transfer?

Blastocyst culture and transfer is an assisted reproductive technology (ART) treatment that can help people or couples who are having difficulty conceiving. Blastocyst transfer is an apparent technological improvement in IVF that involves the strategy of incubating embryos in the laboratory for an extended period of time. Culturing the embryo for such an extended period provides numerous benefits. As the embryo develops further throughout the prolonged culturing process, it is only transferred to the uterus if it is able to make it from the early cleavage stage to the blastocyst stage. After fertilization, blastocyst culture lasts for five or six days, whereas standard embryo culturing lasts only for two to three days.

Also read: Ferty 9 and its Blastocyst Culture and Transfer

Why Choose a Day 5 Embryo Transfer?

Several options have been proposed to improve the success rate of ART, including extending embryo culture. The rationale for this new strategy is that embryos normally implant in the uterus at the blastocyst stage, and prolonged embryo culture until day five may result in embryo selection that has positive results. During day 5 blastocyst transfer, they are cultured for an extended period of time, allowing embryologists to analyze and discard poor embryos while transferring only the most robust ones. As the embryo develops during the culturing procedure, embryologists analyze its development rate and quality, and only the most viable one is transmitted, resulting in a higher chance of successful implantation. One main advantage is that, compared to standard transfer, blastocyst transfer timing is more in line with this advantageous implantation time frame. Compared to earlier-stage transfers, day 5 blastocyst transfers had higher success rates, better embryo growth, and a higher chance of implantation, all of which led to improved pregnancy outcomes.

Also read: What to Avoid After Blastocyst Transfer?

Why is Blastocyst Transfer Preferred in IVF?

During the early phases of the development of IVF technology, researchers were unable to produce lab culture mediums and incubation techniques that allow embryos to develop into blastocysts. Since then, breakthroughs in embryo culturing techniques have allowed for development to the blastocyst stage. 
During traditional IVF, embryos are developed for two to three days before being placed back into the uterus. At this stage of development, the embryo contains between four and eight cells inside the shell, or zona pellucida, and they must continue to develop inside the uterus for another four to five days before becoming blastocyst-stage embryos that are ready for implantation. It is too early to determine which embryos are capable of blastocyst development when a set of embryos is chosen for uterine placement (embryo transfer) on day two or three after ovulation. 

This is why conventional IVF usually involves transplanting 2-3 embryos. The embryologist, no matter how experienced, cannot tell which embryos can and cannot mature into a blastocyst embryo. So, keeping the embryos in the IVF laboratory for a further 2-3 days promotes blastocyst development and helps the IVF team choose good-quality embryos for replacement. Thus, blastocyst transfer is preferred in IVF, as it increases the likelihood of successful implantation and pregnancy.

Factors Affecting Blastocyst Transfer Success Rates

Additionally, there are also other factors that determine whether embryos reach the blastocyst stage or stop developing during the early cleavage stage. Day 5 blastocyst transfer success rates depend on the following: 

• Age of the woman: Maternal age is an important factor in influencing pregnancy outcome. As a woman matures, her ovarian reserve and the quality of the eggs she produces begin to deteriorate. This affects the possibility of the embryos developing effectively during culture, thus affecting embryo survival.
• The quality of the embryos: When the eggs are fertilized and deemed to be cultured, their initial quality is a crucial factor in whether the embryo survives to day 5 or fails during the early cleavage stage.
• The endometrial lining: It is the innermost layer of the uterus where embryos implant. If the lining is not thick enough or not prepared, the chances of pregnancy may decrease.
• Previous fertility treatments: Women who have had unsuccessful reproductive treatments, like in vitro fertilization (IVF), may have a reduced success rate with blastocyst transfer.
• Medical conditions: Uterine abnormalities or fallopian tube issues can impact the likelihood of pregnancy after blastocyst transfer.
• Lifestyle variables: Smoking, alcohol consumption, and obesity can have a adverse impact on fertility and pregnancy rates after blastocyst transfer.

Success Rates of Blastocyst Transfers

The maternal age of the woman having a blastocyst transfer has a considerable influence on the blastocyst transfer success rate. As in other nations, age is an important factor influencing the result of IVF or other assisted pregnancy techniques. Other than maternal age, a number of other factors can influence the likelihood of pregnancy following embryo implantation. However, a woman's age, which is related to a number of biological changes, has a significant role in determining pregnancy rates.

• Women under 35: Their odds of becoming pregnant and having a healthy childbirth are slightly higher than those of other age groups, with a higher success rate.
• Women between 35 and 37: They have a slightly lower chance of successfully transferring blastocysts. A noticeable decline in fertility rates is seen. 
• Women between 38 and 40: As aging continues, women experience fertility decline, and the chances of achieving a pregnancy and giving live birth with blastocyst transfer become very low. 
• Women over 40: Compared to younger age groups, women over 40 who are nearing menopause have the lowest odds of a healthy pregnancy and a live birth. Despite a significant decline in fertility, new technological developments give hope.

Challenges and Limitations of Blastocyst Transfer

Blastocyst transfer can be challenging due to poor embryo survival during extended culture, which reduces the number of viable embryos. It necessitates advanced laboratory conditions and knowledge, which raises costs and complexity. Furthermore, some patients might not produce enough embryos to make this method effective.

How to Improve Success Rates with Blastocyst Transfer?

To improve blastocyst transfer success rates, the following strategies can be followed:

• Good-quality embryos: Culturing embryos to the blastocyst stage provides for improved selection of viable embryos, which increases implantation chances.
• Preimplantation Genetic Testing (PGT): Screening embryos for genetic abnormalities ensures that only healthy embryos are transferred, improving blastocyst transfer success rates.
• Optimized Uterine Environment: Implementing the uterine lining's adaptability with embryo transfer timing improves implantation.​
• Single Embryo Transfer (SET): Reducing the number of embryos transplanted decreases the risks of multiple pregnancies while maintaining success.
• Lifestyle Factors: Maintaining a healthy weight, avoiding stress, and following a balanced diet and activity can all help improve outcomes.

These measures, tailored to individual needs, are supported by advanced techniques and expert guidance at fertility clinics. Because of the embryo's enhanced growth and improved synchronization with the uterine environment, which increases implantation potential, day 5 blastocyst transfer success rates are usually higher.​

Who is a Good Candidate for Blastocyst Transfer?

In general, good candidates for blastocyst transfer can include:

• Women under 35 years old, as fertility decreases with age.
• Women with good-quality embryos, as confirmed by laboratory tests.
• Women have a normal uterus and healthy fallopian tubes.
• Women who have not previously received other fertility procedures, such as in vitro fertilization (IVF)
• Women who are in good general health and have no medical issues that could influence fertility.

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Conclusion

Blastocyst transfer in IVF is a game-changing development in assisted reproductive technology. It has various advantages over conventional transfer methods. The procedure improves the chances of successful implantation, reduces the risk of multiple pregnancies, and allows for better and good-quality embryo selection. Each case is unique; therefore, careful consideration of possibilities such as cleavage-stage embryo transfer, frozen embryo transfer, and preimplantation genetic testing is essential. The developing landscape of IVF offers promise and possibility, with higher pregnancy success rates that give hope to infertile couples struggling to start their family for a long time.

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