Washington, May 14 : Australian researchers have used a technique, DNA fingerprinting, for the first time to identify which embryos have implanted after in vitro fertilisation (IVF) and developed successfully to result in the births of healthy babies.
According to researchers, the technique - combined with sampling cells from blastocysts (the very early embryo) before implantation in the womb - opens the way to pin-pointing a handful of genes that could be used to identify those blastocysts most likely to result in a successful pregnancy.
Researchers believe that their findings will revolutionise IVF by improving pregnancy rates and eliminating multiple pregnancies.
When couples attend fertility clinics for IVF, eggs from the woman are fertilised with sperm from the man and then the fertilised eggs are allowed to develop in the laboratory until they reach the blastocyst stage after about five days.
Before implanting the blastocysts into the woman's womb, a decision has to be made about how many should be implanted and which ones look most likely to develop successfully.
Presently, there is no reliable way of differentiating between viable and non-viable blastocysts, and clinic staff tend to decide on the basis of some fairly crude tests, which include looking at the form of the blastocyst.
As a result, couples often decide to have more than one blastocyst implanted in a bid to raise their odds of a successful pregnancy.
However, this runs the risk of multiple pregnancies with all the associated dangers to both the mothers and babies.
And once multiple embryos are transferred, it becomes impossible to work out which are the ones that developed into a successful pregnancy, making it hard to develop criteria for identifying viable blastocysts.
"DNA fingerprinting is the ultimate form of biological identification, but until now it has not been used to identify the embryonic origin of resultant babies born following embryo transfer; nor has it been used for gene expression studies," Dr David Cram, senior research scientist at the Monash Immunology and Stem Cell Laboratories, Monash University, Australia, said.
"We have developed a novel strategy of utilising a combination of blastocyst biopsy, DNA fingerprinting and microarray analysis to identify viable blastocysts among the cohorts transferred to patients. Our ultimate aim is to find out which genes are expressed by viable blastocysts," he added.
For the study, researchers recruited 48 women undergoing IVF treatment, and after eggs were fertilised and developed in culture for five days, removed between eight and 20 cells from the trophectoderm cell layer of the resulting blastocysts.
These samples were amplified and their gene expression analysed using microarrays. One or more blastocysts were transferred to all 48 women and 25 became pregnant, with 37 babies being born.
In seven women all the blastocysts implanted, in 18 women some implanted and some did not, which indicated that there was not a problem with the uterus, and in 23 women none of the blastocysts implanted, which indicated that either all the blastocysts were non-viable or that the uterus was not receptive.
When the babies were born, blood from the umbilical cord or swabs of cheek cells were taken and stored.
The researchers used DNA fingerprinting on these samples to match them with the DNA obtained from the blastocyst biopsies, thereby identifying which embryo grew into which baby.
Then they used microarray to analyse the genetic message and find out which genes were expressed in the viable blastocysts.
The study is still under process, but researchers have already identified the genes known to be involved cell adhesion, cell communication, cellular metabolic processes and response to stimuli - key processes involved in embryo implantation - are expressed in the viable blastocysts.
Dr Gayle Jones, a co-author and senior research scientist at the Monash Immunology and Stem Cell Laboratories, said: "We believe that it will be possible to refine our gene set to a smaller number of genes that is more highly predictive of a blastocyst's viability and ability to develop to a term pregnancy when transferred to a receptive uterus than current selection criteria."
"The ability to select the single most viable embryo from within a cohort available for transfer will revolutionise the practice of IVF, not only improving pregnancy rates but eliminating multiple pregnancies and the attendant complications," he added.
The study is published online in the journal Human Reproduction.