Women’s eggs attract some sperm more than others – here’s why

Fertilisation of an egg with sperm. (PHOTO: 
Mark Garlick/Getty Images)
Fertilisation of an egg with sperm. (PHOTO: Mark Garlick/Getty Images)
Mark Garlick/Science Photo Library

You may think he’s the one – but what do your eggs think?

In much the same way a fussy a singleton swipes left (or right) when browsing through prospective suitors on a dating app, experts believe women’s bodies can somehow “choose” sperm, making sure it is high quality and genetically compatible.

A recent study, conducted by scientists at Stockholm University and Manchester University NHS Foundation Trust, suggests that human eggs use chemical signals to attract and choose sperm.

“This is the first time this has been described in humans, or in any other species with internal fertilisation,” says John Fitzpatrick of Stockholm University in Sweden.

He and his colleagues studied samples of sperm and follicular fluid – the nutrient-rich liquid that surrounds an egg while it develops and when it’s released – that were collected from 16 couples undergoing fertility treatments, reports New Scientist.

Another surprising result was that for some women, their eggs didn’t always agree with their choice of partner.

“We expected to see some sort of partner effect, but in half of the cases the eggs were attracting more sperm from a random male,” Fitzpatrick told CNN.

“The most likely explanation for this is that these chemical signals allow females to choose males who are more genetically compatible.”

The researchers knew that eggs release chemicals during ovulation known as chemoattractants, which Fitzpatrick says act like a “breadcrumb trail” for sperm to track down the egg.

“We hope it will advance fertility treatment and may help to understand some of the ‘unexplained’ infertility in couples. There might even be a treatment to help eggs attract a partner’s sperm better,”
Professor Daniel Brison, senior author of the study at Manchester University NHS Foundation Trust

In this study, they found that as little as 18% of sperm can even find the trail. When they do pick up on the signal, the sperm swim more vigorously towards the egg, increasing the chances of fertilisation.

Experts believe it’s possible that eggs are more attracted to genetically compatible sperm, which may increase the chance that they’re fertilised, Fitzpatrick says.

The chemical interactions between eggs and sperm after sex may also play a role in why some people have difficulty conceiving.

In around one in three couples who have fertility problems, there’s no clear cause, Fitzpatrick says

 “We hope it will advance fertility treatment and may help to understand some of the ‘unexplained’ infertility in couples. There might even be a treatment to help eggs attract a partner’s sperm better,” adds Professor Daniel Brison, senior author of the study at Manchester University NHS Foundation Trust.

Compared with other animals, humans aren’t very good at making babies, reports Mail Online.

Just 250 individual sperm make it to a woman’s fallopian tube after sex, and only around 25 are capable of fertilising an egg to get her pregnant.

Sources: Royal Society Publishing, News Scientist, CNN, NY Post, Daily Mail