Why transfer multiple embryos?
The reason why more than one embryos are transferred is certainly not the achievement of a multiple pregnancy. Our aim is a single pregnancy by transferring one high quality, chromosomally normal embryo.
However, based on the morphological criteria used to date, it is not possible to always make direct conclusions about an embryo's true quality and developmental competence, nor about its chromosome constitution. It has been suggested that the human is a subfertile species, with 20% monthly fertility rate, compared to primates (80%) or rabbits (90%). It has been shown that 50% of preimplantation embryos have chromosomal abnormalities, and either do not implant at all, or result in early pregnancy loss a few days after implantation.
Chromosomal abnormalities increase with advanced age. For example, a 35 year old woman has a 1/280 chance to have a baby with Down syndrome, while for a 45year old woman the chance is 1/30. Recent studies showed that for women older than 40 years, the possibility of aneuploid oocytes ranges from 5—90%, and therefore is the main reason why older women have a lower pregnancy rate. The other reason is that they have a reduced ovarian reserve.
Based on the above, it is clear why we transfer more than one embryos. Our aim is one healthy baby for each couple having IVF treatment. Multiple pregnancies are now considered a side effect, and there is an international tendency to reduce the number of transferred embryos.