Modern reproductive technologies allow embryos to be cultured in laboratory conditions up to the blastocyst stage—typically the 5th day after fertilization. At this stage, embryos have a higher potential for implantation, and their transfer into the uterine cavity is often associated with increased chances of pregnancy.

Why can blastocyst transfer be more effective?
There are several reasons why transferring embryos at the blastocyst stage is considered more physiological and promising:

• Closer to natural conditions. In a natural cycle, the embryo enters the uterus precisely at the blastocyst stage. Therefore, this timing aligns with the body’s natural rhythm.
• Better embryo selection. Culturing until day 5 allows the exclusion of embryos with delayed development or potential genetic abnormalities. This increases the chances of successful implantation and a healthy pregnancy.
• Reduced risk of multiple pregnancies. Due to the higher implantation potential of blastocysts, usually only one or two embryos need to be transferred. This reduces the risk of twins or triplets and the related complications for both mother and baby.

When might blastocyst transfer be inadvisable?
Despite its high effectiveness, the method may not be suitable for everyone. For patients with low ovarian reserve or a poor ovarian response to stimulation (few eggs retrieved), blastocyst transfer may carry certain risks:

• When there are only a few embryos, there is a chance that none will reach the blastocyst stage in the lab.
• Despite advancements, the artificial environment cannot fully replicate the conditions inside the body. Embryos that fail to develop to the blastocyst stage in vitro may continue developing if transferred earlier into the uterus.

In such cases, it may be more reasonable to perform an earlier embryo transfer (on day 2 or 3 of development) to give them a chance to continue growing in the natural environment.

At VitroMed Clinic, specialists select the optimal day for embryo transfer individually, taking into account the patient’s age, egg quality, history of previous attempts, and overall reproductive health. This personalized approach significantly improves the chances of a successful pregnancy.