What Is Blastocyst Culture and Transfer?
In a standard IVF cycle, embryos are transferred to the uterus (womb) usually on day 5, when they have reached the blastocyst stage – which is typically more than 100 cells.
Blastocyst culture extends the laboratory period by two additional days, giving embryos the chance to reach day 5, known as the blastocyst stage. At this point it has formed two distinct structures: the inner cell mass (ICM), which forms the fetus, and the trophectoderm, the outer layer that develops into the placenta.
Blastocyst transfer means this more developed embryo is placed into your uterus. The difference lies in selection: a clinical team can determine which embryos have the potential to reach this stage, which may improve In Vitro Fertilisation (IVF) success rates.
At Concept Fertility, we aim to culture to the blastocyst stage wherever your cycle allows. That extra time helps our embryologists make a more confident transfer decision.
How Embryologists Monitor and Grade Blastocysts
Our embryology team actively monitors your developing embryos. At Concept Fertility, the laboratory uses EmbryoScope time-lapse imaging, (at no cost to our patients, unlike most other clinics who charge extra for this service), so embryos are continuously observed without being removed from the incubator.
Every day, the embryologists will look to see how many of them have divided and assess their quality, and will keep you informed of any developments that require patient input.
When the embryos develop to the blastocyst stage, they use a 3-character grading system that focuses mainly on the Inner Cell Mass (ICM), the Trophectoderm (the outermost layer of cells), and the degree of expansion and size of the embryo.
Under IVF culture conditions, only about 50 to 70% of human embryos progress to the blastocyst stage after 5 days. Several eggs (oocytes) may have initially fertilised, but not all of them will progress to the four-cell stage on day two, and to the eight-cell stage on day three in culture. The embryos that survive to this stage of development are more likely to be strong, healthy, and robust.
Benefits of Blastocyst Culture
The core advantage of blastocyst culture is embryo selection. At the six-to-eight-cell stage, embryos can look very similar, but two more days allow embryologists to see which have the resilience to reach the blastocyst stage.
Day 5 Blastocyst Transfer Success Rates
Research consistently shows that blastocyst embryo transfer is associated with higher implantation and pregnancy rates per transfer, compared to cleavage-stage transfer. The HFEA confirms this, and roughly three quarters of UK IVF patients now have a day 5 transfer.
Day 5 transfer does not improve any individual embryo’s quality, but it does give your clinical team better information to select from.
Why Transfers Occur on Day 5
The timing of a day 5 transfer is designed to mirror natural conception. After fertilisation in the fallopian tube, the embryo travels toward the uterus over three days, arriving as a morula around day 4, and reaching the blastocyst stage by day 5.
This is when a fertilised egg typically reaches the uterus through the fallopian tube. A blastocyst typically begins embedding into the uterine lining on day 5 or day 6, which is why cell cultivation usually halts at this time.
What Happens After Blastocyst Transfer?
The Day of Transfer and Progesterone Support
Blastocyst transfer is a short procedure, similar to a cervical screening, which can be performed without anaesthesia and only takes around 10 to 15 minutes. You will then be prescribed progesterone to support the endometrial lining and sustain early implantation. Side effects such as bloating or mild cramping are normal.
When to Take a Pregnancy Test After Blastocyst Transfer
The typical wait may be slightly shorter with a blastocyst transfer – around 9 days after because the embryo is already more developed. Your clinic will schedule a blood test to confirm whether implantation has occurred. We recommend waiting for this official test rather than using home kits, as the results could be misleading.
Frequently Asked Questions About Blastocyst Transfer
Is there an additional charge for blastocyst culture at Concept Fertility?
No, Concept Fertility does not charge separately for blastocyst culture and transfer, although many other clinics do. Extended culture is included in your IVF cycle.
What is a frozen blastocyst transfer?
A frozen blastocyst transfer involves thawing an embryo that has been grown to the blastocyst stage and transferring it into a prepared uterus during IVF. The frozen blastocyst is carefully warmed on the day of implantation; this avoids the need to harvest new eggs.
What are the success rates for transferring two blastocysts?
Transferring two blastocysts can increase pregnancy chances per cycle, but significantly increases the possibility of twins and any associated complications. Single embryo transfer is recommended as best practice. At Concept Fertility, we discuss the number of embryos to transfer with each patient individually.
How long do transfers take?
Around 10 to 15 minutes. It is usually painless, and patients can often go home straight after, though some patients experience mild cramping, bloating, or spotting.
Schedule a Consultation with a Specialist
If you want to understand whether blastocyst culture and transfer is right for you. and could form part of your treatment plan, our consultants are here to help.
Call us on 020 3388 3000 or book a consultation online to discuss your journey. Concept Fertility is an independent, clinician-led clinic in Putney, South West London – we offer a free 15-minute mini consultation for patients just beginning to explore their options.