IMPROVING THE ODDS: Scientists have devised a new method for determining which embryos created via in vitro fertilization have the best shot at becoming newborn babies. Image: © ISTOCKPHOTO/MARTIN LLADO
There's new hope for the more than 7 million American women (and their partners) who long for a child and are plagued by infertility. Australian researchers have developed a method for screening embryos created through in vitro fertilization (IVF) to select the ones that have the best shot of developing into healthy babies.
The process, reported in Human Reproduction, utilizes DNA fingerprinting (an assessment of active genes in a given cell) to boost the success rate of IVF and lower the chances of risky multiple births by identifying which of several five-day-old embryos are most likely to result in pregnancy The new method, which will replace unproved alternatives such as choosing embryos based on their shape, is likely to up the success of women becoming pregnant and lower their chances of having multiple births.
In IVF, eggs from a woman are fertilized by male sperm in a Petri dish and allowed to grow for five days until they become blastocysts consisting of about 50 to 65 cells. Because there are currently no precise methods for selecting viable embryos, couples typically choose to implant multiple blastocysts to enhance their chances of conceiving, which may also result in multiple pregnancies.
According to the study, about 42 percent of women who go through in vitro fertilization today become pregnant; of those, 32 percent give birth to twins, triplets or even more babies, according to the Centers for Prevention and Disease Control.
A woman carrying multiple embryos has a greater risk of complications during pregnancy and delivery, which is more likely than a single birth to be by C-section. Their infants are more likely to be low weight or have birth defects.
"What we want this technology to achieve is confidence to switch to single embryo transfers instead of the practice of transferring multiple embryos without [an accompanying] reduction in pregnancy rate," study co-authors Gayle Jones and David Cram, senior research scientists in immunology and stem cells at Monash University in Australia, wrote in an e-mail. They stress that increasing success rates while also reducing the number of multiple pregnancies is a major hurdle in the IVF field.
In this study, the researchers removed eight to 20 cells from the trophectoderm (outer layer) of the blastocysts of 48 women undergoing IVF. The trophectoderm is a cluster of cells that matures into the placenta (the protective sack around an embryo that supplies it with nutrients from its mom and removes its waste). The scientists then scanned the samples using microarray technology, which cuts genetic material into segments to provide a snapshot of which genes are active and which are asleep inside the cells. Twenty-five of the study subjects became pregnant after their embryos were implanted and gave birth to 37 babies; nearly half of them had more than one child.
After the babies were delivered, researchers took blood from their umbilical cords and swabbed their cheeks for DNA samples to compare with those taken from blastocysts at implantation. They found that hundreds of genes active in the newborns were also active in the blastocysts from embryos that survived but not in those that failed. Some of those matching genes are vital for embryo survival, including several responsible for cell communication, cellular energy and adhesion to the lining of the uterus.
"We would like to get down to a panel of about 200 [genes] that we would prospectively test to see which are the most predictive of outcome," Jones and Cram said. "We would then ideally like to have a panel of five to 10 genes that could be tested" quickly in an IVF lab to finger the embryo with the best chance of ensuring a successful pregnancy.
James Adjaye, a biologist at the Max Planck Institute for Molecular Genetics in Berlin, Germany, says that further work needs to be done before scientists can be sure that the genes found in the new work are actually indicate that an embryo will develop into a baby. "Once this has been achieved," he explains, "we will be seeing a new era of pre-implantation genetic diagnosis aimed at, identifying disease-free blastocysts, identifying developmentally competent blastocysts among a cohort developing in vitro and achieving single blastocyst transfer in order to avoid multiple births."