Diagnostic Technique Improves IVF Success Rates

Researchers at the University of Cambridge (United Kingdom) developed a noninvasive method of accurately predicting the likelihood that an embryo will develop not only to the blastocyst stage but also to birth, from as early as two hours after fertilization. The method is based on the discovery that fertilization initiates a series of pulsating movements in the cytoplasm--caused by an interaction between the sperm and the cortex of the egg--that coincides with pulsations of the fertilization cone formed when the sperm and egg plasma membranes fuse to draw the sperm into the egg. Using time-lapse recordings of the cytoplasmic movements and pulsations of the fertilization cone over a period of two hours after fertilization, the researchers charted the frequency of these movements in mouse zygotes.

The recordings showed a linear relationship between the speed of the movements and the likelihood that an embryo would develop to the blastocyst stage. This allowed the group to develop a mathematical model enabling them to predict successful development beyond this stage – all the way to birth. Since similar movements occur in human embryos, these movements should be similarly predictive of embryo viability in humans. The discovery provides a quantitative method of determining embryo viability, which is much more reliable than current qualitative visual inspection. The study was published in the August 9, 2011, issue of the journal Nature Communications.

“There is a need to ensure that the embryos which are implanted into the mothers are those which stand the greatest chance of resulting in a successful live birth,” said lead author Prof. Magdalena Zernicka-Goetz, PhD, of the department of physiology, development, and neuroscience. “It is important to be able to quantitate some indication of the health of embryos at the earliest possible stage in order to minimize the time they have to spend outside the body of the mother.”

Normally, embryos are implanted after two or three days in culture, with their progress at this stage used as a predictor of their likely development. However, around half of all human embryos stop developing before the blastocyst stage, at day five of development. Patients are therefore often implanted with many embryos at once, which can lead to multiple pregnancies. In order to improve success rates and reduce the number of multiple pregnancies, which are potentially risky for the mother and often end in miscarriage, many IVF clinics delay implantation until embryos have reached the blastocyst stage, and implant fewer embryos per round of treatment.

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