A new study, published in the journal Science Advances, found that the female reproductive tract may trap slower moving sperm, allowing only the fastest moving sperm to reach the egg.
Researchers from Cornell University used several models and computer stimulations to try to better understand how sperm travel through the cervix, into the uterus, and then into the fallopian tubes on their path to finding an egg to fertilize. They tested both human and bull sperm and found similar results with both. They found that weaker, or slower moving sperm, got caught in strictures in the female reproductive tract while faster moving sperm were able to pass these strictures.
“Strictures inside the sperm swimming channel play a gate-like role,” the study authors explained. “Sperm with velocities higher than a threshold value can pass through the stricture, whereas sperm slower than the threshold accumulate below the stricture.”
These study findings are not unexpected, but they give us a better understanding of the sperm cells’ journey and why so many sperm cells never reach the egg. The “gate-like behavior of the stricture suggests a motility-based selection mechanism that may potentially be used by the female reproductive tract,” explained the researchers.
The gate-like behavior of the strictures may also help us understand why intrauterine insemination is a an effective first-line fertility treatment for couples with male-factor or unexplained infertility. Intrauterine insemination places the sperm at the top of the uterus, allowing it to bypass the cervix and lower portion of the uterus, thereby also bypassing these gate-like strictures.
If you are struggling with infertility, one of the first steps you may want to consider is having a semen analysis performed to look at sperm count and motility. After a thorough infertility evaluation, if it turns out that you have male-factor or unexplained infertility, you may want to speak with your physician regarding the option of doing an intrauterine insemination. This is a safe and simple procedure that may help increase your chance of conceiving a pregnancy.