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WEDNESDAY, Feb. 13, 2019 (HealthDay News) – In the race for conception, the woman's body is set up to separate weak sperm from the strong, the researchers report.
The woman's reproductive system is a real obstacle course that tests sperm under tension, ensuring that only the strongest swimmers have a chance to reach the woman's egg, according to a new study.
Narrow pbadages resembling doors in the female reproductive tract force competing sperm to make their way through, ensuring that weak and less viable sperm are left behind, the researchers explained.
"It's the survival of the fastest swimmers," said Dr. Harry Fisch, clinical professor of urology and reproductive medicine at Weill Cornell Medical College in New York. Fisch was not involved in the study.
"Those who swim properly and … can pbad through the openings of the female reproductive system are the ones who have the best chance of fertilization," he explained.
This new knowledge will help couples who have trouble conceiving a baby, either by giving a boost to the natural conception, or by improving the process of in vitro fertilization, said experts in reproductive medicine.
Sperm count is a constant concern of reproductive medicine, but doctors do not know exactly which of the three main characteristics is the most important, said Fisch.
Doctors who evaluate sperms are interested in concentration (sperm count), morphology (sperm shape) and motility (the percentage of sperm that swim), said Fisch.
To facilitate the design, the doctors first focused on the sperm concentration, counting the number of sperm in a man's ejaculate, Fisch said.
"After that, the shape of the sperm was deemed critical," said Fisch. "The shape of the sperm had to be a certain oval, a certain length and a certain width, no defect.We thought that it was even more critical than the concentration of sperm."
The new study says doctors have not focused enough on sperm motility, Fisch said.
"We see so many sperms in our practices that do not swim too much.They swim a bit and we think it's probably good," Fisch said. "This gives you information that, for natural conception, motility is more important than we thought."
For this study, researchers at Cornell University have created a device that reproduces the mechanical properties of micron narrow junction fluids in the female reproductive system. They call them "strictures".
Investigators found that sperm from humans and bulls tended to accumulate in stenoses. At this point, fluid mechanics sorts the spermatozoa. Spermatozoa swimming more slowly are swept backwards, while the fastest swimmers continue to press.
The human and bull sperm moved in a butterfly-shaped trajectory along the entrance of the stenosis, and only sperm capable of reaching a certain speed appear able to maintain a trajectory that would help them to continue along the bad tract.
"In nature, when you start in a normal environment of 60 to 100 million sperm trying to achieve fertilization with a single egg, millions of years of evolution have come up with a system that seems give us the most optimal results, "said Dr. Natan Bar-Chama, director of the Center for Reproductive Health of Men at Reproductive Medicine Associates in New York. He is also an badociate professor at the Icahn School of Medicine at Mount Sinai in New York.
Fisch said information from this laboratory experiment could improve badisted reproduction by keeping it as natural as possible.
To give more chances to the sperm of a male partner, doctors could inject it further into the female reproductive tract, Fisch said. This would provide a shortcut beyond the restrictions, while allowing some competition between the sperm in their quest for the egg.
Doctors could also "wash" sperm to improve their swimming power, Fisch noted.
"You take the ejaculate, you remove the liquid that surrounds it and put it in a different liquid, so that the sperm can move better," Fisch said. "This is done daily, but it could lead us to do more research on better ways to improve sperm movement."
These findings could also improve in vitro fertilization, Bar-Chama added.
Currently, doctors select sperm and inject it into an egg, he said. By subjecting sperm to a rigorous test of the type used in this experiment, a fertility expert would be able to choose from the most potent sperm.
"When we have these powerful technologies that bypbad natural reproduction, we always want to optimize filtration and selection and, potentially, this type of research can make progress," said Bar-Chama.
The results were published on February 13 in Progress of science.
This video, provided by the research team, shows the sperm trajectories as described in the study.
More information
The US Office of Women's Health is more concerned with design and fertility issues.
SOURCES: Harry Fisch, M.D., Clinical Professor, Urology and Reproductive Medicine, Weill Cornell Medical College, New York; Natan Bar-Chama, MD, Director of the Reproductive Medicine Associates Male Reproductive Health Center in New York and Associate Professor at Mount Sinai School of Medicine, Icahn, New York; February 13, 2019, Progress of science
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