There is ample evidence to show that as millions of human sperm cells swim towards a waiting ovum or egg, only one gets to fertilize it. Now, a new study shows that even though the fastest and most capable sperms reach the ovum first, it is the egg that has the final say on which sperm fertilizes it.
Human eggs use chemical signals to attract sperm. New research from Stockholm University, Manchester University NHS Foundation Trust and The University of Manchester shows that eggs use these chemical signals to “choose” sperm. Different women's eggs attract different men's sperm – and not necessarily their partners..
Shettles found sperm containing a Y chromosome were smaller, would swim faster and have a shorter life span than the sperm containing an X chromosome. He believed that if a couple had sex around the time of ovulation the male sperm would be more likely to reach the egg before the female sperm.
Once the sperm have entered the uterus, contractions propel the sperm upward into the fallopian tubes. The first sperm enter the tubes minutes after ejaculation. The first sperm, however, are likely not the fertilizing sperm. Motile sperm can survive in the female reproductive tract for up to five days.
Millions of sperm enter the race to fertilize, but only one wins the sprint to the egg. Now Yale researchers have discovered that these winning sperm possess a few key molecular characteristics that differentiate them from those left behind, they report Dec. 1 in the journal eLife.
One explanation has to do with the chromosomes in sperm. The Y chromosome, which makes boys, contains less DNA than the X chromosome for girls. That means sperm that bear a Y chromosome swim faster in viscous liquids. Such a liquid exists at the tip of a woman's cervix in the form of a thick mucous.
If the egg likes the sperm, it sends chemical signals that tell it to swim faster. However, if the egg doesn't like the sperm, the signals it sends encourage the sperm to slow down. It's proper law of attraction at work, with the egg actually ghosting the sperm it's not interested in.
Only a very small fraction of ejaculated sperm actually make it all the way to the egg. Around 300 million sperm are typically released during sex, but only about 200 sperm will reach the egg.
A 2015 study found that the first fraction of ejaculate contains the highest concentration sperm, and that these sperm move more effectively and are of a higher quality than those later in ejaculate.
If she has sex five days before she ovulates, her probability of pregnancy is about 10 percent. If she has sex on the day of ovulation, or the two days before, the chance of getting pregnant is around 30 percent.
Fast-swimming sperm can reach the egg in a half an hour, while others may take days. The sperm can live up to 48-72 hours. Only a few hundred will even come close to the egg because of the many natural barriers that exist in a woman's body.
The sperm rapidly swim up and into the cervix, where they can survive in the mucus for up to five days before an egg is released. When the egg is released at ovulation, it is covered in sticky cells, which help the fallopian tube to catch it.
Some studies suggest that moderate ejaculation (2–4 times per week) is associated with a lower prostate cancer risk. However, ejaculating more often doesn't mean your cancer risk drops even more.
An egg can be fertilized if you have sex anywhere from approximately five days before ovulation until the day of ovulation. The best chances of pregnancy are when sperm are present in the fallopian tube, ready to meet a just-ovulated egg.
Finally, the egg can affect which sperm wins the race with the chemicals it releases in the follicular fluid that surrounds the egg. That's the part which contains the chemical breadcrumbs eggs use to attract and guide sperm to their goal.
The next time you have sex, the number of sperms is not as much as the first time, but the quality of sperm remains stable, and that quantity is enough for fertilization to occur. This proves that having sex twice in a row is still possible to get pregnant if there is no reasonable protection.
Peak male fertility is around 25-29 years old. Sperm quality begins to decline at 30. At 45, men begin to experience a significant decrease in semen volume. Older men can also take longer to conceive a child.
How much sperm does it take? In theory, a single sperm is all it takes to get pregnant. But even in a large amount of semen — such as the quantity in one ejaculation — only a fraction of the sperm are healthy, moving, and sufficiently well-formed to cause a pregnancy.
Semen quality and age
According to a study conducted in Israel, a man's sperm is in optimal conditions between the ages of 30-35. And in general, after age 55, sperm quality is found to be at the lowest quality.
Sperm would have a 5% probability of surviving more than 4.4 days and a 1% probability of surviving more than 6.8 days.
The fast-swimming sperm can take about 30 mins to reach the egg while others might need days. Generally, sperm can survive in the female reproductive tract for up to 5 days (12- hours). The sperm just disintegrates and is washed out of the female tract in due time.
These may include: Abnormal sperm production or function due to undescended testicles, genetic defects, health problems such as diabetes, or infections such as chlamydia, gonorrhea, mumps or HIV. Enlarged veins in the testes (varicocele) also can affect the quality of sperm.
How many sperm do you need to get pregnant? It takes just one sperm to fertilize a woman's egg. Keep in mind, though, for each sperm that reaches the egg, there are millions that don't. On average, each time men ejaculate they release nearly 100 million sperm.
It also suggests that people should not exceed 10 days of sexual abstinence. A 2018 study suggests that ejaculatory abstinence periods of more than 4 days have a detrimental effect on sperm. One 2015 study suggests that daily ejaculation does not have any major negative effects on sperm quality.