Extended culture (blastocysts)

What does this involve?

A variation on standard infertility treatment is to extend culture beyond the normal 2-3 days so that the embryo develops further into a blastocyst (see picture below).In this technique, embryos are moved from a simple culture medium to a more complex one on day 3, but otherwise are cultured in exactly the same way. The prolonged culture means that the best embryos select themselves out and thus each embryo transfer may have a higher chance of success.

This figure shows a typical day 2-3 embryo above compared with a blastocyst to the right. Note that the blastocyst is more developed with a cavity having formed in the middle

Who is this suitable for?

This approach is not suitable for all couples. Patients that might benefit from extended culture and blastocyst transfer include those with repeated IVF failures despite having large numbers of fertilised eggs each time.

On average, only 50% of early embryos will develop to the blastocyst stage. As a result, some couples choosing blastocyst transfer may not have any embryos at all to transfer. Because of this, we normally only recommend this treatment for couples with at least six fertilised embryos.

Freezing may be more difficult. Most blastocysts can be successfully frozen but some patients may produce blastocysts that are not able to survive freezing.