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Fertility 101: A Quick but Necessary Recap!

13 February 2026 · 6 min read min read

📋 This article is for educational and self-advocacy purposes only. It does not constitute medical advice. Always consult your healthcare provider for decisions about your health and fertility treatment.

You have decided it is time for a baby – and that is fantastic! In theory, you know how it works, but …. really, how does it work?!

For conception to be successful and result in a pregnancy, 4 elements are needed:

  • A normally functioning female cycle (including egg or 'oocyte' production)
  • Sperm production on the male side
  • Sexual intercourse and fertilization, all during the fertile window
  • Successful embryo implantation

If, for whatever reason, any of these 4 elements cannot happen naturally, this is when you may need a doctor's help.

Let's start at the beginning.

A few key female hormones to know…

  • FSH (follicle stimulating hormone): stimulates egg development
  • LH (luteinizing hormone): triggers ovulation
  • Estrogen: builds uterine lining, affects cervical mucus
  • Progesterone: maintains uterine lining after ovulation
  • AMH (anti-Müllerian hormone): indicates ovarian reserve (how many eggs remain)
  • hCG (human chorionic gonadotropin): the "pregnancy hormone" that maintains early pregnancy

The Female Cycle: the Big Monthly Preparation

It took science a long time (until the 1930's!!) to fully understand and acknowledge how the female cycle works. Basically, humanity understood the combustion engine before the female cycle inner workings ... Yep, that's right. So, we won't frown if you aren't super sure of how it works. Really.

In any case, here is the low-down:

Phase 1: Menstruation (cycle days 1-5)

Day 1 of your cycle is indeed the first day you get a full menstrual flow!

Your body sheds the last cycle's uterine lining, signaling a fresh start, and resetting everything inside.

Hormone levels are at their lowest, giving your system a break and reset.

Note … that is why the days leading up to and day of your period can feel "off"! Culprits = hormones that all take a break.

Phase 2: Follicular Phase (cycle days 1-14)

In the first few days of the cycle, your brain releases some hormone called FSH, telling your ovaries to start maturing eggs.

Multiple "follicles" then begin developing in your ovaries (that is the "antral follicle count" or "AFC"). Usually only one follicle in one ovary becomes dominant in a natural cycle - rarely 2.

Meanwhile, estrogen levels rise as follicles grow, causing your uterine lining to thicken in preparation for a potential pregnancy later on. See estrogen as being to your uterus what your protein shake is to your work-out!

Phase 3: Ovulation (around cycle day 14)

The main event is a surge of another hormone, LH, which triggers the release of a mature egg from the dominant follicle.

And once released …. this precious egg has about 12-24 hours to be fertilized by a sperm. Yep, that's it. 2 weeks of prep for … 12 hours of life. Crazy, right?!

At this point, your body will give you some clues that you are in your fertile window:

  • Cervical mucus becomes clear and stretchy (like egg whites)
  • Your body temperature may rise slightly
  • Some women also feel ovulation pain

Phase 4: Luteal Phase (cycle days 15-28)

Your egg has released and was hopefully fertilized … if trying to conceive.

Either way, the empty follicle that released the egg becomes the "corpus luteum" (that means "yellow body" in Latin … because it looks yellowish due to its lipid/cholesterol content!). That "yellow body" produces progesterone, which is precisely what maintains the thickened uterine lining, allowing pregnancies to hold.

Now, there are 2 possible outcomes from this cycle:

  • If pregnancy occurs, the embryo will then start producing hCG to maintain the corpus luteum, and there will be no menstrual period, no hormonal reset.
  • If not … well, hormone levels drop and menstruation begins – back to square one.

If any of the above goes wrong …. That is when you may have issues conceiving. Stay tuned for our "Causes of Infertility" article for more on this!

The Male Side: Continuous Production

Unlike the female cycle, our ancestors, way back, already had some form of understanding that something happened with the male body during sexual intercourse, that led to a pregnancy. It's just … that the details weren't quite right yet, as they thought for a while the male deposited the baby indirectly inside the female's womb 😆.

In reality, here is what happens in the male body:

  • Sperm creation: unlike women who are born with all the eggs they will ever have, men continuously produce new sperm. The process takes about 74 days from start to finish for each "batch".
  • The journey: sperm are made in the testicles, mature in the epididymis (a small organ in the back of each testicle), and travel through the vas deferens during ejaculation. They're mixed with seminal fluid to create semen.
  • Numbers game: a typical ejaculation contains 40-300+ million sperm, but only a few hundred will reach the Fallopian tubes. And more importantly …. only ONE can fertilize the egg.
  • Quality matters: sperm need good motility (movement), morphology (shape), and count to successfully reach and penetrate the egg.

In short: it all happens within less than 3 months, with no hormonal peaks or drops, no menstruation … and basically without much effort, really, compared to the female cycle. [sigh]

Fun fact: which sperm fertilizes the egg is actually decided by the egg, not the other way around!! 😉

The Fertile Window: Timing Is Everything

There are 2 key elements to remember: fertile window + male ejaculation are necessary to conceive.

The fertile window is a short, 6-day period, around ovulation. Those 5-6 days of your cycle are when you should have intercourse at least every other day if "TTC" (trying to conceive).

You can ONLY get pregnant during the 5 days before ovulation as well as on the day of ovulation. That's because:

  • Sperm can survive in the uterus and Fallopian tubes for up to 5 days, waiting for an egg
  • The egg can live up to 12-24 hours in your womb, waiting for a sperm to fertilize it
  • Peak fertility is the 2-3 days before ovulation, when cervical mucus is most sperm-friendly and estrogen levels peak

In a natural conception, once the egg is released, it starts traveling from the end of one of the tubes (called fimbriae), slowly down to the uterus. It is normally met by the sperm in a specific place within the tube, where fertilization happens.

There are tracking signs you can learn to understand, to help determine your fertile window:

  • Cervical mucus becomes clear, stretchy, and abundant
  • Basal body temperature rises slightly after ovulation
  • LH surge is detected by ovulation predictor kits aka "OPKs" (more rarely bloodwork)

Inside the Uterus: the Implantation Process

After the egg has been released, and sperm have reached the egg, fertilization may occur.

At peak fertility (women in their 20's), this is about a 1 chance in 3 for fertilization to occur. That means out of 3 menstrual cycles, the sperm will fertilize an egg only during 1 of these cycles. And this stat actually diminishes as the female ages: at age 40, there is only a 5% chance of an egg being fertilized by a sperm in a given cycle.

Mind-blowing numbers, I know!

However, once fertilization happens, here is what happens in your body:

  • Days 1-6 after ovulation: once the sperm has fertilized the egg, the newly formed "embryo" continues its travel into the uterus, while dividing and growing very quickly.
  • Days 6-12: the rapidly-evolving embryo finds a spot in the uterus, and attaches to the uterine lining: this is implantation. This is when pregnancy hormones (hCG) start being produced, at very low levels initially.
  • The perfect environment: the uterine lining must be thick enough (typically 7mm+) and hormonally primed by estrogen and progesterone to support implantation.

Sometimes, however, things go wrong, and the above doesn't happen …

  • Ovulation issues (PCOS, thyroid problems, stress disrupting hormone signals) — there may not be ovulation, or a faulty one
  • Tubal problems (blocked, damaged or removed fallopian tubes) — can prevent egg and sperm from meeting
  • Uterine issues (fibroids, polyps, adenomyosis, thin lining or an infection) — can interfere with implantation even if fertilization happened
  • Male factors (poor sperm quality, or very limited or non-existent sperm) — reduces the chances of fertilization
  • Complex and rare issues (such as immune disorders or blood-clotting disorders) — more investigation may be needed
  • Sometimes, the problem is "unexplained": all tests are normal, but pregnancy still doesn't occur.

Age and Fertility: the Harsh Reality

For women, egg quality and quantity decline with age, especially after 35. This affects both natural conception and IVF success rates.

For men: while sperm production continues throughout life, quality can decline with age, affecting DNA integrity and motility.

Issues can happen on both sides, and can then create hurdles to pregnancy.

The Bottom Line

Fertility and whether pregnancy can happen depend on multiple systems working in perfect harmony - hormones, timing, egg and sperm quality, and a receptive uterus. It is not surprising that sometimes, it can take quite a while before pregnancy happens!

When natural conception doesn't happen, medical intervention can help identify and address specific issues.

Understanding these basics can help you navigate fertility treatments with confidence and ask the right questions from your medical provider about your unique situation.

See our other articles Infertility 101: Where to Start? and Causes of Infertility, for further information. (Coming soon!)