Two very common client questions:
How many embryos should be transferred?
How many embryo transfers will be needed to achieve a pregnancy?
The answer to both questions is it depends.
There is medical science to direct us to the answers to those questions. Here we present solid information based on research.
In most all cases the of embryos to transfer is one. Transferring more than one does not mean pregnancy success rate will be higher, nor does it 100% mean that there will not be more than one baby. Embryos from IVF split at a higher frequency than they would in nature.
The table below is reproduced from the 2017 guidance published by the American Society of Reproductive Medicine (www.asrm.org)
This guideline from the ASRM is very similar to that put forward by the European Society of Human Reproduction and Embryology (www.eshre.eu)
Multiple studies have shown that single embryo transfer is preferred over double.
Publications supporting elective single embryo transfer (eSET).
ASRM (via SART) data showing transfer of more than one embryo does not lead to higher pregnancy rates.
Elective single embryo transfer in women less than age 38 years reduces multiple birth rates, but not live birth rates, in United States fertility clinics
Reference Link: https://pubmed.ncbi.nlm.nih.gov/27376458/
Example recent study in 2018 showing one per transfer is best.
One Plus One Is Better Than Two: Cumulative Reproductive Outcomes Are Better after Two Elective Single Blastocyst Embryo Transfers Compared to One Double Blastocyst Embryo Transfer
Reference Link (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6094541/)
Another 2018 study showing increasing number of embryos transferred does not increase live birth rate.
Live birth and multiple birth rates in US in vitro fertilization treatment using donor oocytes: a comparison of single-embryo transfer and double-embryo transfer
Reference Link: https://pubmed.ncbi.nlm.nih.gov/29931407/
The practice of eSET has been dramatically increasing and now the normal.
Percentages of Elective Single Embryo Transfer (eSET) Among All Transfers Using Fresh Embryos from Fresh Nondonor Eggs, by Age Group,* 2007–2016 (Data from the CDC)
Note: This data set ends before the ASRM guideline suggesting eSET in 2017.
Number of embryo transfers needed?
A large study across all ages but with euploid embryos.
In a study analyzing 4,515 patients who had up to three consecutive single embryo transfers of euploid embryos, 94.9% achieved a pregnancy. Pregnancy rates were highest for the first transfer for a euploid embryo: it stood at 69.4%. Implantation rates for the second euploid transfer were 59.3% and for the third, 59.2%. (source).
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