Why didn't my egg fertilise after ICSI ?

A patient just sent me this email.We had our 1st cycle in July this year with ICSI as I had just turned 45 years and my partner is same age, we had a very good grade 1 embryo put back but didn't implant.So we have just now had another cycle on the 24th November this month, I had a mature egg follicle size was 19 mm sperm was good they done ICSI again but this time they said it didn't fertilize ?They told us the egg was good and the sperm was good but it just didn't happen.How can I have a good egg and sperm but didn't fertilize using ICSI . I could understand it if the egg wasn't a good one or sperm, and how come we had a grade one embryo few months ago and now nothing?Does this sound right to you ? ICSI with a good egg good sperm but no fertilization I cant get my head around I've been so upset.This was my answer to her.Yes, this is frustrating, but it's quite common to have failed fertilisation after ICSI when women are more than 40 years of ageThis is because the egg may look good, but because it has aged, the mitochondria ( the energy powerhouses of the cell)  in its cytoplasm do not have enough  ability to be able to power cell divisionThis is why a woman's fertility drops as she gets older !The limitation with IVF technology today is that we cannot test the mitochondrial competence of the egg .
Source: Dr.Malpani's Blog - Category: Reproduction Medicine Source Type: blogs