A team of British and Japanese researchers set out to discover the factors that determine a successful conception and the hurdles that sperm encounter in their journey to produce a healthy embryo.
The findings revealed sperm's swimming ability isn't the only influencing element; a major role is also played by the pattern and rhythm in which they move, and which can be described through a simple mathematical formula.
The study, published in the journal Physical Review Letters, offers new insight into the reproductive system and could bring important contributions to the development of male fertility treatments.
Race Toward The Egg: A Treacherous Journey
After unprotected intercourse, more than 50 million sperm enter the marathon toward the fallopian tubes. The liquid environment they are traversing is relatively hostile and few survive its trying conditions.
For most of them, the path is hindered by obstacles and dead ends, and they eventually become trapped on their route to the uterus.
The 0.060-millimeter sperm are also hunted along the way by intrepid leukocytes - white blood cells that stand guard, ready to dispatch intruders.
Barely 10 sperm survive to reach their destination, and there can only be one winner: just one individual sperm can fertilize the egg, provided the latter has been released to perfectly synchronize with the sperm's arrival.
"Every time someone tells me they are having a baby, I think it is one of the greatest miracles ever - but no one realizes," says Hermes Gadelha, study author and lecturer in applied mathematics at the University of York.
Rhythm Or Blues
What makes the tenacious sperm successful and causes the others to fail? Gadelha's team uncovered that aside from sperm motility, count, and morphology, the rhythm in which they swim upstream to the fallopian tubes is also important.
Tests showed the head and tail of the sperm move in specific patterns, which resemble the fields forming around magnets and whose function is to propel the sperm closer to the egg.
To better understand how male reproductive cells are able to swim in the encompassing fluid, the team analyzed the tails of individual sperm and measured the rhythm of their movements. As they discovered, these cells describe specific rhythmical patterns that enable them to reach their destination.
In other words, for couples trying to conceive, off-rhythm sperm can cause a lot of heartache.
The team was able to synthesize the pattern in a mathematical formula and plans to test how it could be used to anticipate the movement of large sperm counts.
"The more we know about sperm the better," says Professor Allan Pacey, an expert from the University of Sheffield, who believes this formula might provide a new direction in infertility treatments.
