Turbo-charged sperm speed through a dimly lit canal, coursing feverishly through vast landscapes and titanic cavities. A lone egg desperately awaits her suitor, pledging her life if left unavowed. Then, the swiftest sperm rises from the depths of darkness, breaking through a fortress wall and presenting himself to his prospective partner. A union is formed. The end.
This is the stuff of movies and drama. But it’s also the stuff of fertilisation. When sperm are released into the vaginal canal, an intricate performance ensues. With the ovaries serving as arc lights, the stage womb is set.
Every month, one amongst a woman’s two ovaries releases a mature egg into the fallopian tube. This egg remains available for fertilisation for about 24 hours, and if met by a sperm, can lead to conception. Sperm can survive for up to 5 days within the uterine cavity, so it is possible that you will get pregnant if you’ve had intercourse in the 5 days leading up to ovulation.
It’s wise to maintain an ovulation calendar to preempt your fertile periods. Conception involves millions of sperm vying to outpace each other in order to reach the available egg. Only one sperm wins, achieving fertilisation after a long and arduous journey. The resultant embryo, still in the fallopian tube, then descends downward until it reaches the uterine cavity, where it implants itself.
The Steps of Fertilisation
Fertilisation is a complex process, with the female body working in mysterious ways to align the egg and the sperm. Detailed below, are the steps that go into it.
Step 1. Ovulation
Ovulation refers to the emergence of a single mature egg from one of the ovarian follicles. The egg only has a 24-hour window to be fertilised. During this time, vaginal discharge becomes wet and slippery, a telling sign that fertility is at its peak. Other ovulation symptoms include bloating and abdominal pain. If unprotected intercourse is had during this time or in the 5 days prior, there is a good chance that it will result in a pregnancy.
Step 2. Ejaculation
Semen is a versatile substance, providing both nourishment and protection for sperm. As soon as ejaculation happens, the semen left behind forms a wall across the vagina to save sperm from moving downward. This wall lasts only about half an hour before it starts to trickle out of the vagina. The sperm cells that do make it through after ejaculation begin a long journey up the cervical canal, each holding out hope to make it to the egg first.
Step 3. Journey Through the Cervical Canal
The cervical canal is a warm and conducive environment that allows sperm to thrive and push on in their journey. Generously lined with cervical mucus, the canal is tailored for sperm transportation, especially during the fertile window when mucus is at its maximum. Interestingly, the days before ovulation will herald molecular changes that you may not even be aware of. Microscopic threads of molecules line up along the cervical canal, to allow sperm to latch on as they pace through.
Step 4. Biochemical Alterations + Accelerated Movement
Sperm that enter the cervical canal must change their structural form in order to survive. Their new environment triggers biochemical changes that allow them to travel at breakneck speeds through the uterus and fallopian tubes.
Step 5. Branching Off
Once sperm reach the uterus, they have a critical decision to make. Do they go right or left? There’s a fallopian tube on either side and it’s anybody’s guess which tube has released an egg this time. Sperm tend to branch out at this point, some gravitating to the left and others to the right. Sperm that pick the correct tube has a significant chance of reaching the egg in time. Now, with about half the competitors as before, sperm must power to the finish line in time.
Step 6. Fertilisation
Only the most resilient sperm reach the egg and even the ones that do must cross another hurdle before they can reach their final destination. Every egg is covered with a tough outer layer and hundreds of sperm engage in a race to see who can penetrate first. When one sperm finally does manage to achieve fertilisation, the egg immediately experiences chemical changes that block other sperm from entering. Then, the chromosomes in the egg and sperm combine, giving rise to a zygote.
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Step 7. Implantation
The zygote divides repeatedly over the next few hours and days. It gradually rolls down through the fallopian tube, reaching the uterine cavity about a week later as a 100-cell ball. The zygote now implants itself into the uterine lining, going on to develop into a baby.
As frenzied as the fertilisation process is, it marks the beginning of a chapter that will unfold page by page over the next nine months. By being in the know of how fertilisation works, you can stay better prepared in planning your family. So that when the arc lights in your womb are turned on, you’re still the director of the show.
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