Sperm TEAM up to reach the egg, study finds

Sperm team up and swim in shoals like fish heading upstream in the fallopian tubes to reach a woman’s egg, a study has found.

Researchers at Cornell University, in Ithaca, New York, and North Carolina A&T (NC A&T) revealed those in groups were more likely to swim in a straight line and — when there was a current — were less likely to be swept away. But they were not faster than their rivals going it alone.

Scientists said the research could help with selecting sperm for use in the fertility treatment in-vitro fertilization (IVF), because the method removes natural checks on weaker sperm found in the female reproductive system.

More and more couples are having to opt for IVF because people are having children later or due to tumbling sperm counts leaving them struggling to conceive. Several thousand babies are born via the method in the U.S. every year.

In the study — published Thursday in the journal Frontiers in Cell and Developmental Biology — researchers looked at the behavior of sperm from bulls, or male cows.

This is a good comparison, as the sperm are similar to those from humans, unlike in mice where the cells have hooks to grab onto each other.

In the experiment the sperm were put through small tubes in a microfluidic device, which mimicked the boundaries of the female reproductive system.

This was filled with a viscoelastic fluid similar to that in the female reproductive system, which had about the same consistency as melted cheese. 

Its flow was then altered to see how the sperm responded, with some swimming together at each stage.

When there was no flow, the scientists saw that sperm in groups changed direction less often and were more likely to swim in a straight line.

But when this was raised slightly, the clustered sperm were better aligned and appeared ‘like a school of fish heading upstream’.

Scientists also tested a rapid flow, finding that sperm who stayed together were less likely to be carried away. 

But the research team also noted that the grouping behavior did not lead to sperm cells swimming faster than their rivals.

Dr Chih-Kuan Tung, a physicist at NC A&T who co-authored the research, said: ‘In general, I would say that identification of [movement] advantages that are not speed enhancement is not usual, and therefore significant.

‘In some ways we open new avenues for examination of sperm performance.’

She added: ‘In the longer term, our understanding may provide better selection of sperm used for intervention such as in vitro fertilization or other assisted-reproduction technologies.

‘This may be needed as [these methods] typically skip some or all of the selection mechanisms present in the female tract and yield less favorable results.’

Several thousand babies are born via IVF every year in America, figures from the Centers for Disease Control and Prevention suggest.

But more than two-thirds of all procedures carried out end in failure — such as the fertilized egg failing to attach to the womb lining.

In IVF, sperm cells are put through several steps to determine which will be best for fertilizing the egg.

This includes placing another fluid on top of the semen and monitoring for which sperm swim into it, and separating the cells by density.

The scientists hope that tests for the movement of sperm could be used in another example.