ICSI, pICSI, IMSI…now there’s a new kid on the block.
Rescue ICSI
Rescue ICSI (rICSI) was banned in the UK by the HFEA until recently. It’s the process where a second attempt is made at fertilising eggs using ICSI, after conventional IVF has failed. After the publication of the Best Practice paper on the Use of ICSI in ART by ARCS and the BFS in 2023, the HFEA rescinded this prohibition. Until now, the safety and efficacy of rICSI has remained uncertain, but last week an addendum to the Best Practice paper was added.
After a systematic review of outcomes after rICSI, evidence does not support previous concerns that rICSI might result in higher levels of birth defects in children, although the data is still quite limited.
What happens in the lab?
Conventional IVF insemination is the process of adding a certain number (approx 100,000) of motile sperm to eggs that have been taken from the ovaries earlier the same day, then waiting for one of those sperm to get through the shell of the egg and initiate fertilisation. There are two time-points when checks can be made to see if rICSI might be needed; 6 hours after the IVF insemination (on the same day as egg collection), or 16-18 hours after IVF insemination (the morning after egg collection). Mature eggs that show no signs of fertilisation are then injected with a single sperm, and those eggs are checked again for fertilisation after a further 16-18 hours.
Timelapse incubators are a must so that fertilisation events can be monitored and recorded at all times of day and night. If doing rICSI 16 hours after insemination, the recommendation is to freeze any resulting embryos and replace in a frozen cycle, in order to ‘resynchronise’ the embryo and lining of the womb.
Who might benefit?
Fertilisation rates with conventional IVF typically average 55-65% of all eggs collected. However, even when sperm parameters appear normal, fertilisation rates can be lower, and in approximately 5% of cases none of the eggs might fertilise. If unfertilised eggs are mature with no signs of fertilisation, rICSI might be able to salvage the situation, with approximately 65% unfertilised eggs going on to fertilise normally following rICSI.
Overall, rICSI is still only recommended in cases of very low or no fertilisation with conventional IVF, but this may change as more long-term data becomes available. The technique itself is exactly the same as ICSI, it’s just performed later than normal when conventional IVF hasn’t worked.
Remember, the number of eggs available is likely to be small – but in cases where only a few eggs have been collected, this could make the difference between having an embryo to transfer and not. It’s a big commitment from the laboratory to fit this in to normal daily workloads, so it may take some time before it is considered as routine practice.
