How does pregnancy actually work?

Have you ever stopped to think: How does pregnancy really work?

The journey that leads to pregnancy is a truly awe-inspiring feat by our bodies, and a collaboration in a way, between the sperm and the egg, aided by hormones.

In this blog post, we'll unveil the steps involved in how pregnancy works, from the woman's menstrual cycle to fertilization and beyond.

We'll also explore the woman's role, the different phases of her cycle, and the significance of the man's contribution to preganancy.

Whether you're actively trying to conceive, simply curious about the human body, or planning for the future, we at Arva made this guide for you, to help you understand your journey and empower you in the process!

So, read on!

What do you need to conceive?

Reproduction is complicated, but at its most basic core, a few elements are absolutely required for a healthy pregnancy and live birth to take place:

1. A high quality and genetically normal egg

2. Healthy sperm

3. A functional fallopian tube

4. A uterus that is able to hold a pregnancy

5. Hormonal support for each event

To simplify, a healthy egg and a healthy sperm are both needed. They need a place to meet (the fallopian tube) so that fertilization can happen.

The fertilized egg (now called embryo) makes it way down the fallopian tube to implant itself in the uterus for the next 9 months.

Each event must be supported by the presence of the right hormone, in the right amount, at the right time.

What is the women's role in reproduction?

It’s impossible to understand the process of reproduction without understanding the role of hormones and the menstrual cycle.

Picture an orchestra. The hormones that control the menstrual cycle are the conductor. If the conductor is late, misses cues, or doesn’t show up at all, the whole concert falls through.

In this section, we’ll explain what ideally takes place during the menstrual cycle to make reproduction happen.

The Menstrual period

Here’s a quick overview: there are different sequences of events that happen with hormone levels, with the ovaries, and with the lining of the uterus during a typical 28 day cycle.

From a timing perspective within the average 28-day menstrual cycle, these sequences can be thought of in three main chunks: the start when the period begins, the follicular phase during which an egg matures in an ovary, and the last 12-14 days called the luteal phase.

For cycles that are a different length than 28 days, the last 12-14 days are relatively fixed as the luteal phase, and the remainder of the time is the follicular phase. Ovulation happens at the end of the follicular phase, and the exact cycle day depends on the length of the cycle.

The Menstrual cycle

Each month, hormones prepare the uterus to receive a fertilized egg and to allow for implantation of an embryo. When implantation doesn’t happen, the lining of the uterus that has thickened during the last cycle, sheds in what’s known as menstruation or a menstrual “period.”

The first day of menstruation is considered day 1 of the menstrual cycle.

The Follicular Phase

Simultaneously with the menstrual period ("menses" as seen below), follicles begin to grow.

Follicles are sac like structures that contain growing, immature eggs.

During the follicular phase, a hormone called follicle stimulating hormone, or FSH, is released from the pituitary gland in the brain. FSH tells these follicles to grow.

Every month, a bunch or group of follicles is selected to grow.

On day 7 or 8 of the cycle, one dominant follicle (or occasionally two) is selected for continued growth and to ultimately release “the egg of the month”. The rest of the follicles do not mature but instead, degenerate.

Hormones in the follicular phase

As FSH supports the growing follicles, the follicles also release estrogen. And estrogen prepares the uterus for a pregnancy.

The cells that line the uterus are collectively called the endometrium. The endometrium must grow in this duration in order for successful implantation to occur when the embryo is ready.

The thickening of the lining of the uterus, or endometrium, is dependent on estrogen—and in the right amount.

Hence simultaneously the endometrium thickens as well, preparing itself for implantation.

The Ovulation Phase

Around the middle of the cycle, the process of ovulation begins.

To trigger ovulation, a hormone called luteinizing hormone, or LH, is released. LH helps the egg in the dominant follicle to continue to “mature.”

In simplistic terms, the most important part of this maturation process is the egg shedding half its DNA blueprint to make space for the sperm DNA (remember mitosis and meiosis from school folks? This is meiosis 🧬).

The follicle then ruptures and the mature egg is released. Once the egg is released, or what’s known as ovulation, the luteal phase begins.

The Luteal Phase

When the egg ovulates, the fallopian tubes come into play. The fallopian tubes essentially vacuum the surface of the ovary and bring the now-mature egg into the tube to meet the sperm.

Of course, that means there needs to be sperm waiting in the fallopian tube to meet the egg when it is ovulated or very soon thereafter.

The egg usually degenerates within 24 hours after ovulation. For now, let’s assume the sperm is where it needs to be at the right time, and we’ll cover the details on how that happens soon. (Just know, this probably means intercourse happened in the 72-hour window leading up to ovulation, though sperm can live up to 5 days in the reproductive tract.)

The corpus luteum

While the egg is waiting around in the fallopian tube, the follicle that released it transforms into something called the corpus luteum.

The corpus luteum releases estrogen and progesterone which are both essential for implantation in the uterus.

Fertilisation

Meanwhile, in the fallopian tube, sperm try to enter the egg by piercing its outer layer, called the zona pellucida. When one sperm penetrates the egg, “fertilization” happens.

Over the next few days, the cells of the fertilized egg divide and create an embryo. It divides rapidly, from 2 cell to 4, 4 to 8, 8 to 16 cells and so on.

After about three days of growth, the embryo (at this stage called the morula), begins to make its way down the fallopian tube to its new home, the uterus.

Implantation

In the uterus, the embryo continues to grow, becoming what’s known as a blastocyst. It then “hatches” and starts the process of implantation.

When the endometrium is receptive, it is in a way a signal for the embryo, allowing it to embed itself in the endometrium. The embryo is pulled in, sticks, and invades the endometrial lining.

Hormones during the implantation phase

When implantation happens, the hormone human chorionic gonadotropin, or hCG, is released.

This hormone might sound familiar because it’s the one that’s measured in pregnancy tests. HCG keeps the corpus luteum (the ruptured empty follicle where the egg used to be) alive so that it continues to release estrogen and progesterone.

Estrogen and progesterone support the endometrium during this second half of the menstrual cycle, and in turn, the endometrium supports the growing embryo until the placenta has formed.

The pregnancy process, a puzzle of hormones

If any tiny piece of this process is missing, there won’t be a pregnancy. In that case, the corpus luteum goes away 12 or 14 days after ovulation. That means the hormonal support for the endometrium disappears, and we are back where we started—the menstrual period—where much of the endometrial lining sheds in a woman’s period, starting the whole cycle again.

It’s important to note that these are just the steps leading to the beginning of a pregnancy—there are a lot of other things that must go right to maintain this pregnancy and eventually lead to a live birth over 9 months.

The male role in pregnancy

Everything we just said assumes that sperm is not only where it needs to be at the correct time, but that the sperm functions correctly.

But reality is different.

Male factor infertility (MFI) is believed to play a role in 30%–50% of all cases where couples are having trouble conceiving. For more information on the topic, we suggest you look at our course here specific to MFI.

Sperm production

Men’s role in reproduction starts well before conception, as new sperm is produced in the testicles roughly every three months. The main hormones involved in sperm production are actually the same ones we saw in the female cycle, but they’re used in different ways—LH controls the production of testosterone, and FSH controls the production and maturation of sperm.

When a man ejaculates into the vagina, sperm travels through the vas deferens and urethra, and is released along with seminal fluid, or semen.

Semen also plays a key role as its composition can either help or hinder the sperm from swimming to their destination.

Fertilisation

Post ejaculation in the vagina, sperm fight their way to find the egg.

They swim from the vagina, through the cervical mucus, then traverse the cervix and uterus, and finally pass into the fallopian tubes.

While this whole journey is only a few inches long, it’s an incredibly long trip for sperm (which are the smallest cells in the human body).

It’s the comparable distance of a person swimming from California to Hawaii and back.

Unsurprisingly, only a tiny fraction of sperm will make it all the way to the fallopian tube to find the egg.

The Journey of Pregnancy, with Arva

So, there you have it! The fascinating journey of pregnancy, which is a multi-step process with menstruation, ovulation, fertilisation and implantation.

And let's not forget that there’s contribution from both ways. Healthy sperm are the leading role, along with healthy eggs.

Understanding how pregnancy works can be empowering for couples on their family-building journey. It can start with a fertility test, to better equip your journey of trying to conceive, with the information you need.

Remember, if you have any concerns or questions, consulting a healthcare professional is always recommended. They can provide personalized guidance and support throughout this exciting chapter.

And remember, we’re just a call away for any questions or concerns!

You’ve got this!