Using just one embryo during IVF results in a much higher chance of a healthy pregnancy and birth, according to a study presented at the annual meeting of the American Society for Reproductive Medicine.
The study by scientists at the University of Colorado and Duke University, found that there was twice the likelihood of success if just one embryo was used, after controlling for other factors that influence IVF.
'The most impressive finding that has relevance for all patients undergoing IVF is that performing the transfer with one embryo greatly increases the chance of a healthy baby, the desired objective in IVF,' said Dr Alex Polotsky of CU Advanced Reproductive Medicine, who led the study.
The researchers examined data reported to the Society for Assisted Reproductive Technology from 30,000 patients in the USA who underwent IVF using donor eggs between 2012 and 2014.
The most significant finding was that double and triple embryo transfers were much more prevalent among cycles using fresh eggs, which led to a higher incidence of multiple pregnancies. It is well known that multiple births can be associated with complications for the mother and the child – including premature birth and low birth weight.
The study was also the first to compare success rates of IVF using fresh and frozen eggs. Although implantation rates of embryos were slightly better using fresh donor eggs, there was no difference in the chance of a healthy birth using either fresh or frozen eggs.
In traditional IVF using fresh eggs, the donor egg is immediately fertilised and inserted into the uterus of the recipient. For this to result in successful implantation, the hormonal schedule of the egg donor and the recipient need to be aligned.
Using frozen donor eggs offers a cheaper and more convenient way of carrying out fertility treatment. The practice of freezing eggs and cryogenically storing them for use in IVF is becoming increasingly popular.
Irrespective of the source of the donor egg, the most important factor identified as resulting in a healthy pregnancy and birth was to transfer one, instead of multiple, embryos.
'We encourage patients and physicians alike to set their focus on the horizon of achieving a healthy birth outcome. Just achieving a pregnancy is not sufficient,' said Dr Polotsky.