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Female anatomy lets only strong sperm swimmers reach the egg

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A recent research article that sheds light on the role of sperm’s swimming ability on conception. We thought you would want to know.

Strictures of a microchannel impose fierce competition to select for highly motile sperm.


  • In the race to conception, the female body is set up to separate weak sperm from strong, researchers report.
  • A woman’s reproductive system presents a veritable obstacle course that stress-tests sperm, making sure that only the strongest swimmers have a chance of reaching a woman’s egg, according to a new study.
  • Narrow gate-like passages within the female reproductive tract force competing sperm to barge their way through, ensuring that weak and less viable sperm are left behind, the researchers explained.
  • Doctors evaluating sperm look at concentration (the number of sperm), morphology (the shape of the sperm), and motility (the percentage of sperm that are swimming). To aid conception, doctors first focused on sperm concentration, counting the number of sperm in a man’s ejaculate.
  • The new study indicates that doctors have not placed enough emphasis on sperm motility.
  • Tests with sperm from men and bulls revealed that the strongest swimmers were most likely to make it through the tight spots, known as “strictures”, while weaker ones were caught in oncoming currents that propelled them backwards when they got too close.
  • This new knowledge will help couples struggling to conceive a baby, either by giving natural conception a boost or by improving the process of in vitro fertilization.
  • “In nature, when you start off in a normal setting of 60 to 100 million sperm trying to achieve fertilization with one egg, millions of years of evolution have fine-tuned a system that seems to give us the most optimal outcomes,” said Dr. Natan Bar-Chama, director of the Center of Male Reproductive Health at Reproductive Medicine Associates of New York. He’s also an associate professor with the Icahn School of Medicine at Mount Sinai in New York City.

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