The ultimate goal of sperm is to fertilize the egg. However, to meet the egg cell, the sperm has to go through a long and tedious path. After they meet, many people wonder what’s next and how long will it take for implantation to occur and the woman to get pregnant. This article aims to clarify these doubts in detail.
The various sections of this article are assembled in the following table of contents.
How sperm meets egg
In everyday language, we understand by sperm’s journey to the egg the race in which only one sperm cell will make it to the finish line, and win the competition. Although this is an analogy, it actually works very similarly: while many sperms participate in the race, only one of them will be the privileged one that will fertilize the egg.
We can split the journey into two different stages:
- Male reproductive tract: from the testes to the exterior.
- Female reproductive tract: from the vagina, where the semen is deposited, to the Fallopian tubes, where the sperm will meet the egg.
At every single stage, the sperm will have to overcome new obstacles, which you can find explained in the following sections.
Pathway from testes to urethra
It takes about 90 days for sperm to develop and reach the adequate maturity as to be ejected with ejaculation. Spermatozoa are born in the seminiferous tubules of the testes, and then travel to the epididymis.
The seminiferous tubules can be found within the testicles and are responsible for sperm production. The epididymis is a long tube that connects the testicle with the vas deferens.
During intercourse, a large amount of sperm (250 million approx.) leave the epididymis to go through the vasa deferentia and the urethra. Throughout this path, the sperm are covered with fluids released from the seminal vesicles and the prostate, thereby giving raise to what we know as semen, also referred to as ejaculate.
The main function of these fluids is to ease the entrance of the sperm to the vagina. Through the urethra, sperm are shot out out via the penis, thereby entering the female reproductive tract, in particular the vagina.
During the journey from the testes up until it comes out, the sperm acquire the proper form to reach and fertilize the egg. In short, the following are the changes that take place throughout the final stage of the sperm maturation process:
- It packages its DNA to allow for the head (which contains the DNA) to be as small as possible, which makes it easier for it to swim more adequately and go through the zona pellucida (i.e. egg coat).
- The tail develops the ideal structure to allow for the sperm to become stronger and move forward more quickly.
- The mid piece is full of mitochondria to have plenty of energy. It allows the sperm to be more energy-efficient.
What happens to sperm inside a woman
After ejaculation, the sperms leave the man’s body and enter the female reproductive tract, where they begin the second phase of the race toward fertilizing the egg.
Throughout this journey, spermatozoa have to overcome a great number of obstacles or barriers that will make it difficult for them to get to the Fallopian tubes and hit the egg.
The distance sperm travel is about 15 to 18 cm, and they participate in a race against time. It cannot take too long for them to reach the egg once it has been released from the ovary (after ovulation), as the lifespan of an egg is not longer than 24 hours. The survival rate of an oocyte is low if compared to that of spermatozoa, which are able to survive for up to 2-5 days inside the female reproductive tract.
After ejaculating, the sperms begin a race where not only speed is crucial, but also resistance. Those with defects and/or poor motility will not make it to the end.
Some of the obstacles the sperms will encounter include:
- Vaginal pH
- Not every sperm cell is able to survive inside the vagina due to the acidic pH it contains.
- Response of the immune system
- The woman’s white blood cells detect the sperm cells as “enemies”, and try to destroy them.
- Cervical mucous
- Secretions from the cervix and vaginal discharge vary in consistency and texture throughout the menstrual cycle. During ovulation, this fluid is more liquid and less dense to facilitate the passage of sperm. Conversely, when the woman is not ovulating, this fluid becomes denser and viscous, which complicates the sperm’s journey.
- Physical barriers
- The internal anatomy of the female reproductive system (vagina, cervix, uterus, Fallopian tubes) is in itself an obstacle for the sperms. Some sperms get caught in cavities known as vaginal crypts that can be found within the woman’s reproductive tract.
The good news is that everything is not so complicated. The egg tries to pave the way for the sperms by releasing molecules and sending signals. The Fallopian tubes and the uterus use a suction force by creating rhythmic contractions, and the cervical mucous becomes less dense to allow the sperms to travel more easily.
On the other hand, the seminal fluid that accompanies the sperms neutralizes the effect of acidic pH and secretes a sugar that nourishes the sperm. This fluid, at the same time, acts as a protective shield before white blood cells.
Egg fertilization in the Fallopian tubes
Once the vaginal, cervical, and uterine barriers have been overcome, the sperm have to go through the narrowest part of the journey: the utero-tubal junction. Only a few spermatozoa out of the 250 million contained within the ejaculate make it to this stage.
Along the whole length of the path, the most powerful sperm, that is, those which have been able to overcome the obstacles of the female reproductive tract, gain an extraordinary ability: the fertilization capacity, which medical term is sperm hyperactivation. From this moment on, its tail becomes stronger and more powerful so that the sperm cell is able to move with energy and reach the egg more easily.
Once the sperms hit the Fallopian tubes, some of them become attached to the walls, exhausted, and unable to continue in the race.
At this point, only a few sperm are still in the competition, as the vast majority got lost somewhere along the way. Out of the few dozens of sperm that reach the egg cell, only one of them will be the able to walk through the egg cell’s door: the zona pellucida (ZP).
The chosen sperm cell, which is the strongest and most qualified to be so, goes then through a process called acrosome reaction. Through this process, the enzymes that are contained within the acrosome break through it, thereby weakening the ZP and making it easier for the sperm to penetrate the oocyte cell.
An acrosome is a structure that develops over the head of the sperm cell and contains a set of enzymes and other substances necessary for the sperm to be able to penetrate the zona pellucida.
When the sperm goes into the egg, their nuclei fuse together, and that is the process we actually refer to as fertilization.
FAQs from users
After sperm meets egg, how long until implantation?
Implantation occurs approximately within 3-7 days after fertilization, as the fertilized egg cell has to travel from the point where it was fertilized to the point where it implants. It depends on how high the point where they meet in the Fallopian tube is. For instance, if they meet high in the tube, it will take about 7 days.
How many sperm make it to the egg?
To answer this question, I will split the answer into various figures, each one corresponding to a stage in the journey:
- There are approximately 200-250 million sperm in each ejaculation, but only about 2 million make it to the cervix.
- Once there, out of the 2 million sperm entering the cervix, only about 1 million are able to make it to the uterus.
- Out of the 1 million that enter the uterus, only 10,000 are able to travel to the top of this organ.
- Out of the 10,000 that survive at this point, only half of them travel in the right direction, that is, toward the egg cell.
- Out of the approximately 5,000 sperm that enter the utero-tubal junction, about 1,000 get inside the Fallopian tube.
- Finally, out of the 1,000 that enter the tube, it is estimated that only 200 make it to the egg.
However, in the end, only 1 sperm out of the 200 that reach the egg is able to penetrate and fertilize it.
How does it feel when sperm meets the egg?
The truth is, there is no scientific evidence that fertilization can actually produce symptoms in the woman right after conception occurs. However, no study or expert has ever stated that it is either possible or impossible to know. Some women believe they knew the exact moment, while others do not realize. Sensitivity to hormonal changes could be the explanation behind those cases where the woman believes she “felt something”.
How long after IUI does sperm meet egg?
It depends on ovulation. If it has already taken place, fertilization usually takes place within 24 hours before the introduction of sperm into the body, regardless of whether it has been done via natural conception or intrauterine insemination (IUI).
Can sperm meet egg before ovulation?
Fertilization can occur as long as there is an egg waiting for the sperm to fertilize it. An egg can survive for 12-24 hours, but sperm can live up to 5 days or even longer inside the woman’s body. This means that, even if there is no egg in the tube when you have intercourse, if it occurs one week before ovulation and the sperm is still alive when the egg is released, the sperm could meet the egg anyway. In other words, the woman could get pregnant as well.
Where does the sperm go when you have a vasectomy?
Although the testes continue to produce sperm, they cannot pass through the vasa deferentia because they have been cut and tied with the vasectomy. So, they are not expelled with ejaculation, but reabsorbed by the body instead.
When pregnant, where does sperm go?
When a woman is pregnant, the cervical canal is sealed by a cervical mucus plug that protects the baby during pregnancy and prevents the entrance of anything that could damage the baby. Keeping this in mind, sperm are unable to enter the uterus, so their journey ends in the vagina. Most of them will just leak out after ejaculation, while a small percentage might remain there and die within a few days.
When does sperm die outside the body?
Depending on the conditions outside the body, sperm can live from a few minutes to 20 minutes approximately. However, factors such as smoking, air pollution, alcohol, anabolic steroids, STDs, etc. could contribute to lessening this lifespan.
When does sperm leave the female body?
After ejaculation, that is, once the sperm enter the vagina, their lifespan is about 2 to 5 days on average. The most powerful ones will die along the journey, though. After fertilization, both the dead and alive sperm that could not fertilize the egg will be eliminated by means of phagocytosis (i.e. the body’s own system of neutralization and elimination of substances).
How quickly does a sperm meet an egg?
It can take about 45 minutes to 12 hours for a sperm to reach the Fallopian tubes and meet the egg. The fastest sperm are, however, able to reach the egg within 30 minutes approximately, depending on the quality of the sperm.
How many sperm fertilize an egg for identical twins?
Identical twins are formed when a single egg cell is fertilized by a single sperm cell, and the resulting embryo divides into two halves. Conversely, with non-identical or fraternal twins, two eggs are fertilized by two sperm, thereby creating two genetically unique fetuses that will not be more alike than siblings that are born at different times.
Suggested for you
The ultimate goal of the competition is to meet the egg, join it, and give raise to a new cell, which will end with the delivery of a baby 9 months later. In this sense, if you want to learn what happens after fertilization and embryo implantation, we recommend that you visit this post: Pregnancy month by month.
Also, I suggest that you read the following article to know when and how does sperm production occur prior to the beginning of the journey we have just talked about: When do sperm appear during the process of spermatogenesis?