The great sperm race: conception is not that simple

A fertile couple who have regular sexual intercourse, even around the time of ovulation, has about a 20% chance of conceiving a child. That means it’s okay 1 out of 5 times!

This probability should reassure many stork hunters who, after a couple of unsuccessful attempts, worry about their ability to become mothers. No fear! A few months of “marathons” before succeeding is perfectly normal and, moreover, don’t blame yourself because most of the time everything depends on the sperms!

If you’ve seen the National Geographic documentary titled “The Great Sperm Race,” you’ll have seen in detail what happens from intercourse to eventual conception . If you have not been able to see it, I will summarize it here in a few simple main concepts.

The documentary was enormously successful in America and the idea of ​​relating the situation to human scale effectively gave an idea of ​​how complicated it is for the sperm to reach its destination.

The poor spermatozoa (which in the documentary are represented by people dressed in white), have to face an extremely hostile path, and only a few “chosen ones” manage to reach the egg in the right time. Do you think that only 30 minutes after ejaculation 99% of the spermatozoa are dead or dying…

There are millions of sperm cells in a fertile man in each ejaculate but only about 80% are of good quality and therefore with all those useful and necessary characteristics to face the path that separates them from their destination. Also beware of infrequent intercourse. An “old” sperm is scarcely fertile. Old spermatozoa release substances that inhibit good quality ones. So avoiding not having intercourse until ovulation is a highly counterproductive choice. The same happens if intercourse is too frequent, because in this case the sperm is scarce and the sperm are not completely mature.

The right balance is to have intercourse 2-3 times a week even before ovulation.

The vaginal environment is generally hostile due to the pH conditions and the action of the female immune system but it is above all at the level of the uterine cervix that selection is highest. Only a few thousand arrive in the uterus. The famous cervical mucus is represented with a series of tunnels that crush the poor sperms. Clearly if we are in the ovulatory period the mucus meshes are more favorable to crossing thanks to the action of estrogens.

In the uterus, the sperm undergo a strong attack by the woman’s immune system: the leukocytes work to prevent the entry of foreign organisms/cells into the woman’s body and engulf the sperm they manage to trap. Only those who manage to pass this immune barrier unscathed can pass into the tubes. The tubes are very small to find. However, it seems that the spermatozoa are favored in finding the right one (the one in which ovulation took place) thanks to particular contractions of the uterine wall. Access to the tubes is very small and only a few are able to reach it. Here too there is a selection that allows only spermatozoa with the right characteristics to access it.

Very few spermatozoa arrive in the tubes, about less than 10 and here they find an environment conducive to their survival.

In order for the sperm to fertilize the egg, they must enter a particular state called capacitation. But they have to be at the right time, too early or too late it rules him out of the competition.

A single sperm manages to reach its destination also because after having penetrated the ovum this prevents the entry of other sperm and thus avoids multiple fertilization.

It is said that the winning sperm is not the most “beautiful” or the most “intelligent”. It is the one who surely found himself in the right place at the right time.

Kathryn Barlow is an OB/GYN doctor, which is the medical specialty that deals with the care of women's reproductive health, including pregnancy and childbirth.

Obstetricians provide care to women during pregnancy, labor, and delivery, while gynecologists focus on the health of the female reproductive system, including the ovaries, uterus, vagina, and breasts. OB/GYN doctors are trained to provide medical and surgical care for a wide range of conditions related to women's reproductive health.

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