Chennai: A new study has found that a woman’s eggs are especially selective when choosing the most ideal sperm for fertilisation.
“This is the first time this has been described in humans, or in any other species with internal fertilisation,” says John Fitzpatrick at Stockholm University in Sweden.
He and his colleagues studied samples of sperm and follicular fluid – the nutrient-rich fluid that surrounds an egg while it develops and when it is released – that were collected from 16 couples undergoing fertility treatments. Sperm swim through follicular fluid on their way to reach an unfertilised egg.
Looking at leftover samples from 16 couples getting reproductive treatment, researchers found that eggs release a chemical that attracts only certain types of sperm — regardless of whether they come from the woman’s chosen partner, according to the findings published in the journal Proceedings of the Royal Society.
The selectiveness could be a way of sorting out the mate with the best genes, said study author John Fitzpatrick, an assistant professor in the department of zoology at Stockholm University in Sweden.
The researchers examined how sperm respond to follicular fluid, which surrounds eggs and contains sperm chemoattractants. The researchers wanted to find out if follicular fluids from different females attracted sperm from some males more than others.
“Follicular fluid from one female was better at attracting sperm from one male, while follicular fluid from another female was better at attracting sperm from a different male,” said Fitzpatrick.
“This shows that interactions between human eggs and sperm depend on the specific identity of the women and men involved.”
Millions of sperms are released inside the uterus with a single ejaculation. However, the uterus has an entire obstacle course to help narrow down the choices the ova/egg has. These include the acidic pH of the uterus, the thick lining of mucus inside the uterus wall and the various white blood cells (WBCs) that the uterus uses to kill sperms. The female body considers sperms to be a foreign object and hence her immune system reacts to eliminate them.
Also, sperm can stay inside the uterus for about 3-5 days, but an egg only becomes viable for 24 hours.
“The idea that eggs are choosing sperm is really novel in human fertility,” said Professor Daniel Brison, the scientific director of the Department of Reproductive Medicine at Saint Marys’ Hospital, which is part of MFT, and the senior author of this study.
The University of Manchester Honorary Professor added: “Research on the way eggs and sperm interact will advance fertility treatments and may eventually help us understand some of the currently ‘unexplained’ causes of infertility in couples.”
“I’d like to thank every person who took part in this study and contributed to these findings, which may benefit couples struggling with infertility in future.”