What is blastocyst transfer and how does it differ from day 3 transfer? Learn about the evidence, the risks and the effect on how many embryos are frozen.
Blastocyst transfer is the growing of the embryo in the laboratory until about the fifth or sixth day and its transfer to the uterus at the blastocyst stage; in day 3 transfer, the embryo is transferred earlier, at the cleavage stage. Your doctor and embryologist decide together which day will be chosen, according to your number of embryos, their development and your situation. According to a review, a signal in favour of blastocyst transfer was found for live birth in fresh transfer, but the reliability of this finding is low; in the overall result in which fresh and frozen transfers were assessed together, no difference could be shown. In extended culture, some embryos may not reach the fifth day; in this case there may be no embryo left to transfer. The information below offers a general framework; it does not replace a diagnosis or treatment recommendation specific to the individual.
What is a blastocyst, and how does it differ from a third-day embryo?
In the first days after fertilisation the cells of the embryo divide; this is called the cleavage stage, and it is assessed around the third day. A blastocyst is a more advanced stage, reached on the fifth to sixth days, containing an inner cell mass and an outer layer called the trophectoderm. The basic difference between the two stages is how many days the embryo has been grown in the laboratory.
How is a blastocyst graded?
Blastocysts are graded by the Gardner system on expansion level, inner cell mass and trophectoderm. This grade, made up of letters and numbers, summarises the embryo's appearance in the laboratory; it does not mean that a pregnancy will occur.
How does extended culture proceed?
Your embryos are grown in an incubation environment in which temperature and gas ratio are controlled; the embryologist assesses development on certain days. Whether the embryo will be transferred on day 3 or at the blastocyst stage determines how many days culture will be continued.
Do all embryos reach day 5?
No, they may not. In a review, the likelihood of having no embryo to transfer was found to be more common with blastocyst transfer; the reason for this is largely that embryos stop developing before the fifth day. According to another assessment on this subject, in unselected groups of patients cancellation of the transfer is significantly more common with extended culture; in patients with a good prognosis this difference is not seen. This can be an unexpected and upsetting development for you or for your treatment plan; do not hesitate to ask for support. The next step is re-planned together with your doctor.
Is there a single transfer day suitable for everyone?
The current evidence does not show that there is a single ideal transfer day valid for all patients.
Has the benefit of the blastocyst stage been shown in fresh transfer?
A review combined many controlled studies; most of the participants were patients with a good prognosis. A signal in favour of the blastocyst was found for live birth per fresh transfer, and clinical pregnancy was also found in favour of the blastocyst. The reliability of the live birth finding was assessed as low, and that of the clinical pregnancy finding as moderate.
Does the result change when fresh and frozen transfers are assessed together?
In the same review, no marked difference was found in the cumulative pregnancy rate, in which fresh and frozen transfers obtained from the same egg collection cycle were assessed together. According to another assessment on this subject, although there are studies reporting higher live birth in patients with a good prognosis, when the evidence is restricted to studies of higher reliability this difference disappears and no difference remains in cumulative pregnancy; for this reason it is emphasised that the result of a treatment cycle should be assessed on the cumulative births obtained from that cycle. The review also found that the number of embryos to be frozen was lower with blastocyst transfer.
In which patients has it been studied most?
Most of the studies were carried out in patients with a good prognosis. There is no study using donor eggs; not enough studies have been done on women with a poor prognosis and of advanced age. For this reason it is difficult to interpret the results for these groups, and it is not possible to say that it is useful for a particular patient group.
Can the number of embryos to be transferred or stored fall in extended culture?
There are two outcomes that can be expected from extended culture: an increased likelihood of being unable to transfer, and a reduced number of embryos to be frozen and stored.
Is blastocyst transfer linked to twin pregnancy?
According to opinions on this subject, blastocyst culture may be linked to a small increase in identical (monozygotic) twinning; the data are inconsistent, and it is recommended that you be told about a small increase in risk on this subject. In a review, multiple pregnancy remained uncertain when all studies were taken together, while in studies of higher reliability it was reported that it might be increased with blastocyst transfer. The risks of multiple pregnancy, such as preterm birth, are dealt with on the embryo transfer page.
How many embryos are transferred?
According to current guidelines on this subject, whatever the stage of the embryo, single embryo transfer is recommended if there is more than one embryo. In fresh blastocyst transfer, the decision on whether two embryos are transferred should not be based on the appearance or quality of the blastocyst. Transferring blastocysts as a single embryo because of the risk of identical twinning has also been discussed in these guidelines. The number to be applied in Turkey is determined by current legislation and your doctor's assessment.
What happens after the transfer?
We give the details of subjects such as the procedure itself, preparation, medicine support after the transfer and the pregnancy test on the embryo transfer page. Your doctor will tell you the schedule and your medicine plan.
What can you ask your doctor when discussing the transfer day?
- On which day is the transfer planned for me, and what is the reasoning?
- What will be done if the embryos do not develop as far as the fifth day?
- If there are surplus blastocysts, will they be able to be frozen?
- How many embryos are planned to be transferred?
- Is there an additional cost for extended culture?
Frequently Asked Questions
Can a sixth-day blastocyst be transferred?
The rate of development of embryos can differ, and some reach the blastocyst stage later. According to the current expert view on this subject, the live birth rate is lower in blastocysts that develop slowly; in seventh-day blastocysts, chromosome number abnormality is more common and the implantation rate is lower. The rate of development is therefore taken into account in the assessment; but there is no definite rule of the form "it is not used".
Are the outcomes of babies born after blastocyst transfer different?
Assessments on this subject report a possible small increase in adverse newborn outcomes; but it has not been shown that this is a direct cause-and-effect relationship. It is stated that this effect arises largely from the increase in single embryo transfer, that is, from the decrease in multiple pregnancy.
Is blastocyst culture meaningful for those with few embryos?
According to a review, no difference was found according to prognosis; in a small controlled study carried out with women who had two or more failed implantations too, no significant difference was seen in implantation and pregnancy. For this reason no clear benefit or harm can be stated for this group; the approach is determined together with your doctor.
How are surplus blastocysts stored?
In centres that apply extended culture, surplus blastocysts can be frozen and stored; it is recommended that the possibility of freezing (cryopreservation) be available in such programmes. The conditions of freezing and storage depend on legislation and the consent form you have signed; you should confirm the current situation with the centre.
Does a good blastocyst grade show that pregnancy will occur?
No. The Gardner grade summarises the appearance of the embryo in the laboratory. This grade, made up of letters and numbers, is not an assurance of pregnancy.
Do all embryos reach the fifth day?
No. Some embryos may stop developing, and there may be no embryo left to transfer. The next step is re-planned together with your doctor.
Is the transfer day determined only by the number of embryos?
No. Your doctor and embryologist assess the number of embryos, their development and your situation together.
Is blastocyst transfer better for everyone?
No. The current evidence does not show a single ideal transfer day for everyone. Most of the studies were done in patients with a good prognosis.
Does a favourable result in fresh transfer also show that the overall treatment result is better?
This conclusion cannot be drawn. Although a signal in favour of the blastocyst was found for live birth in fresh transfer, its reliability is low. When fresh and frozen transfers obtained from the same collection cycle were assessed together, no marked difference was found in cumulative pregnancy.
Can extended culture reduce the number of embryos to be frozen?
Yes. The review found that the number of embryos to be frozen was lower with blastocyst transfer. You can talk about this possibility when the transfer day is being planned.
Can the results be interpreted with the same certainty at an advanced age or with a poor prognosis?
No. Because not enough studies have been done in these groups, it is hard to interpret the results. The approach is determined according to your circumstances.
Is the appearance of the blastocyst on its own a reason for transferring two embryos?
No. The decision to transfer two embryos should not be based on the appearance or quality of the blastocyst. Guidelines recommend single embryo transfer; in Turkey the number to be applied is determined by legislation and your doctor's assessment.
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