Progesterone 101: Role in Ovulation, Fertility & Pregnancy

Written by:
Team Inito

Health Researchers and Writers
Verified by:
Dr. Shruthi Shridhar

Homeopath & Nutritionist

Written by:
Team Inito

Health Researchers and Writers
Verified by:
Dr. Shruthi Shridhar

Homeopath & Nutritionist

If you’re trying to understand your hormones – whether to get pregnant or just learn about your body – you’ve probably heard of progesterone.

But what is it exactly? And why does it matter so much when you’re trying to conceive? Let’s break it down.

If you’re trying to understand your hormones – whether to get pregnant or just learn about your body – you’ve probably heard of progesterone.

But what is it exactly? And why does it matter so much when you’re trying to conceive? Let’s break it down.

What is progesterone?

Progesterone is a key hormone in your menstrual cycle, specifically during the luteal phase. It’s produced mainly by a structure called the corpus luteum, which forms in the ovary after ovulation.

Progesterone essentially makes your uterine lining cozy and holds the door open for a potential pregnancy. Once pregnancy officially begins, it makes sure that everything is going smoothly.

And even if you’re not trying to conceive, progesterone still matters. It helps regulate your cycle, balances out estrogen, and supports a stable luteal phase.

Progesterone and ovulation - What’s the link?

Let’s walk through your cycle for a moment.

In the first half (called the follicular phase), estrogen is doing most of the heavy lifting. It helps your uterine lining grow and aids in the development of a mature egg in the dominant follicle.
Then comes the LH surge, which triggers ovulation – your dominant follicle releases an egg.
After ovulation, your body shifts gears. That’s when progesterone takes the spotlight.

Once you ovulate, the follicle becomes a structure called the corpus luteum, which starts secreting progesterone. This hormone plays a crucial role in thickening the uterine lining to support a potential implantation, with levels typically peaking around 6 to 8 days after ovulation.

This post-ovulation rise in progesterone is also what helps confirm whether ovulation has actually happened. PdG, a urine metabolite of progesterone, offers an easy way to track this. If PdG doesn’t increase, it’s a sign that ovulation hasn’t occurred.

Let’s explore the hormone charts of two Inito users to see what this looks like.

On the first chart, you’ll notice a steady and consistent rise in PdG (the blue line). This increase is your body’s way of saying that ovulation has happened.

Now take a look at the second chart. The blue line remains more or less the same across several days. That means PdG hasn’t risen from baseline levels, meaning that ovulation hasn’t occurred. This is called anovulation (when your body doesn’t release an egg). It’s more common than you’d think and is actually the leading cause of infertility in women.

So, what happens next in your cycle?

If pregnancy doesn’t occur, your progesterone levels naturally drop. This drop triggers your period.

But if pregnancy does happen, progesterone keeps rising. That’s why you’ll often hear people call it the “pregnancy hormone”, because healthy progesterone levels are critical for a successful early pregnancy.

Curious what your PdG
levels could look like?

Get a free sample hormone chart
showing your 4 key fertility hormones—
PdG, estrogen, LH, and FSH—just by
answering a few questions.

Curious what your PdG levels could look like?

Get a free sample hormone chart showing your 4 key fertility hormones—PdG, estrogen, LH, and FSH—just by answering a few questions.

Progesterone and pregnancy - How it all comes together

Progesterone plays a major role in helping your body not just get pregnant, but stay pregnant. Here’s what it does:

Stops ovulation so your body doesn’t release another egg
Thickens the uterine lining for the embryo to implant
Prevents uterine contractions that could disrupt early pregnancy
Protects the pregnancy by priming your immune system to the growing baby
Preps your body for breastfeeding

The bottom line? Without enough progesterone, your body can’t support a healthy pregnancy. Now, let’s talk numbers: studies show that implantation is most likely to succeed when blood progesterone levels are at least 10 ng/mL. If levels are too low, it can make implantation harder and reduce your chances of getting pregnant that cycle. Curious what normal progesterone levels look like during your menstrual cycle and pregnancy? The table below can give you a helpful reference point:

Stage of menstrual cycle or pregnancy	Serum progesterone level
Follicular phase	0.1 to 0.7 ng/mL
Luteal phase	2 to 25 ng/mL
First trimester	10 to 44 ng/mL
Second trimester	19.5 to 82.5 ng/mL
Third trimester	65 to 290 ng/mL

What’s PdG, and how’s it different from progesterone?

Here’s where things get interesting.

When your body makes progesterone, it eventually breaks it down, and one of its byproducts is PdG (pregnanediol glucuronide).

While progesterone lives in your blood, PdG is the urinary signal that confirms if ovulation has actually taken place.

Let’s simplify:

Progesterone = shows up in blood tests after ovulation
PdG = shows up in urine after ovulation

Why is PdG so useful?

Because there’s a pretty close correlation between progesterone and PdG throughout your cycle. This means that if your blood progesterone levels rise, so will PdG. Similarly, if your progesterone declines, you’ll see a similar trend in your PdG.

How do you measure progesterone or PdG?

Traditionally, doctors measure progesterone through a blood test, typically about 7 days after ovulation. That’s often called a “Day 21 test” (assuming a 28-day cycle). But here’s the thing: progesterone levels can bounce around a lot throughout the day. So, one blood draw might not give the full picture.

And let’s be honest, getting a blood test can be expensive, time-consuming, and not exactly fun.

That’s where PdG testing comes in.

Measuring PdG in urine is a simple, pain-free, and affordable way to confirm if ovulation actually happened. Here’s a quick comparison between progesterone and PdG testing:

Factors	PdG Test	Progesterone Test
Hormone measured	PdG (urine metabolite of progesterone)	Progesterone
Test sample	Urine	Blood
Test format	Non-invasive	Invasive
Convenience	At-home testing	Visit the lab
Hormone trend	Rises after ovulation Peaks at 6-8 DPO	Rises after ovulation Peaks at 6-8 DPO
Normal Range	Before ovulation - 0-3 ug/mL After ovulation - 6-40 ug/mL	Before ovulation - 0.1 - 0.7 ng/mL After ovulation - 2-25 ng/mL
Result	Confirms ovulation	Confirms ovulation
Accuracy	Inito is 96% as accurate as a blood test and confirms ovulation with more than 99% specificity	91-100%

With the Inito Fertility Monitor, you can track PdG, along with 3 other key fertility hormones (LH, estrogen, and FSH), to help you track your fertile window and confirm ovulation right from the comfort of your home.

How to check PdG levels using the Inito Fertility monitor

The Inito Fertility Monitor is a lab-grade fertility monitor that measures four key fertility hormones in your urine. Inito connects to your smartphone and essentially transforms it into a mini hormone lab, giving you personalized, real-time insights into your fertility.

The Inito Starter Pack comes with everything you need to begin your fertility journey. It includes:

The Inito fertility monitor
A phone attachment clip
15 Inito test strips
Urine cup

Once you’ve got your kit, simply download the free Inito app from the App Store to begin. The app will tell you exactly when and how to test. Just:

Pee into a cup
Dip in the test strip
Get your results in less than 10 minutes

Yep, that’s it. No guesswork. No needles. Just clear hormone insights. But here’s a quick heads-up: not all PdG tests are built the same. Some are threshold-based, which means they only tell you “yes” or “no” based on whether your PdG is above a certain level (usually 5 µg/mL). If your result crosses that line, the test says you’ve ovulated. While that’s helpful, it may not always be accurate. That’s why Inito’s PdG tracking gives you real-time, personalized hormone trends, so you can actually see your PdG rise over multiple days and confirm ovulation.

Measure PdG with
actual hormone data

With Inito you get real numerical values of all 4 pregnancy hormones (Estrogen, LH, PdG (urine metabolite of progesterone) & FSH) in just 10 minutes.

Get $50 off (auto-applied at checkout)

FAQs

How can I increase progesterone to get pregnant?

There are many ways you can support your progesterone levels. Eating foods rich in magnesium, zinc, and vitamins B6 and C, exercising regularly, seed cycling, managing stress, and herbal supplements can all help you naturally boost your levels.

What causes low progesterone?

Low progesterone is usually linked to stress, thyroid issues, PCOS, irregular ovulation, or a luteal phase defect. Identifying the root cause is key to getting your hormones back on track.

Why is my progesterone dropping in early pregnancy?

A drop in progesterone can be linked to early pregnancy loss, but sometimes it’s part of a normal shift called the luteal-placental transition. As long as the drop isn’t too early or too steep, it may not be a problem. Progesterone levels should range from 10-44 ng/mL in the first trimester. If needed, your doctor may recommend supplements. Many people go on to have healthy pregnancies even with low progesterone, but always check with your healthcare provider to be sure.

What’s the difference between progesterone and PdG?

Progesterone is the hormone measured in your blood. When progesterone breaks down in your body, it forms PdG, which gets excreted in the urine. PdG testing lets you confirm ovulation happened—easily and non-invasively—from home.

What are the benefits of PdG testing?

PdG correlates closely with blood progesterone trends. So PdG testing can reliably confirm ovulation while being painless, affordable, and convenient. It gives you real insights into your fertility without a blood test.

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PdG levels might look like!

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