Hi folks, I think the argument of whether embryos for IVF should be replaced on day 3 or 5 post-fertilisation have raged on for decades. I will try to explain to you our thinking.
The initial argument for placing day 3 embryos because it is believed that an embryo would develop better and have a greater chance of propagating a baby by being inside the uterus earlier, than it would by being allowed to develop into a blastocyst in an incubator. However, this view is not valid.
The rationale for blastocyst culture and replacement on day 5 is to:
1) improve both uterine and embryonic synchronicity (ie. mimick the natural conception as much as possible whereby the fertilised embryo inside the fallopian tube travels to and usually implants into the uterus by day 4-5 ie. blastocyst stage) and
2) enable self selection of viable embryos (ie. "bad" embryos will die off and not reach blastocyst (day 5) stage; thus, resulting in higher implantation rates. If wait culture (Day 3) early cleaved embryos long enough, the ones that are chromosomally or genetically abnormal will die off (this is akin to natural selection) and only "competent and good" embryos will continue to grow on culture (in the lab's petri dish).
The largest most comprehensive reviewer of current medical evidence, COCHRANE database systematic reviews in 2012 stated that "there is a small significant difference in live birth rates in favour of blastocyst transfer (Day 5 to 6) compared to cleavage stage transfer (Day 2 to 3) from 12 randomised controlled trials (RCTs). However, 4 RCT's have found cumulative clinical pregnancy rates from cleavage stage (derived from fresh and thaw cycles) resulted in higher clinical pregnancy rates than from blastocyst cycles. The most likely explanation for this is the higher rates of frozen embryos and lower failure to transfer rates per couple obtained from cleavage stage protocols. Future RCTs should report miscarriage, live birth and cumulative live birth rates to enable ART consumers and service providers to make well informed decisions on the best treatment option available".
My conclusion from the evidence thus far is that there are merits to both day 3 and day 5 embryo transfers. Day 3 transfers are associated with a higher pregnancy rate whereas Day 5 transfers are associated with a higher live birth rate. How a doctor interprets the results will determine what that doctor chooses.
For me, a higher live birth rate is more important because it is the end result (birth of a baby) which matters. A day 3 transfer may result in more pregnancies , but may also result in more miscarriages (because more "bad" embryos may have been transferred without being selected yet as opposed to allowing it grow until day 5 before transferring) leading to lower live birth rates.
So which of the two embryo transfer options would be more acceptable to you? Day 3 or day 5?