Progesterone is one of the most important hormones to understand when you’re trying to conceive (TTC). While ovulation and estrogen often get more attention, progesterone plays a crucial role in supporting early pregnancy and preparing your body for implantation.
In this article, we’ll cover what progesterone does, how it fluctuates through your menstrual cycle, why it matters for conception, and how to monitor it naturally.
What is Progesterone and What Does It Do?
Progesterone is a sex hormone made mainly by the ovaries after ovulation. Its primary role is to thicken and maintain the lining of your uterus, creating the perfect environment for a fertilized egg to implant and grow.
Once ovulation occurs and the egg is released, your body forms a temporary structure called the corpus luteum. This structure produces progesterone, and levels rise in the second half of your cycle, also known as the luteal phase.
If conception happens, progesterone levels keep rising to support early pregnancy. If pregnancy doesn’t occur, levels will drop, and that hormonal shift is what triggers your period.
Progesterone is essential for:
- Thickening and maintaining the uterine lining
- Supporting embryo implantation
- Reducing uterine contractions
- Helping the body transition into pregnancy mode
This hormone works alongside estrogen to support your fertility journey, and an imbalance—especially low progesterone—can make it harder to get or stay pregnant. A 2020 study showed that the miscarriage rate was lower (9.6%) in women with serum progesterone levels ≥ 35 nmol/L and significantly higher (70.8%) in those with levels < 35 nmol/L.
How Progesterone Works Throughout Your Menstrual Cycle
Progesterone levels aren’t steady throughout your cycle. They rise and fall depending on what phase you’re in. Understanding this rhythm is key to knowing if your cycle is working as it should.
The Follicular Phase
During the first half of your menstrual cycle, called the follicular phase, progesterone levels are naturally low—averaging 1-4 mg every day. This phase is dominated by estrogen, which helps grow the uterine lining and stimulate the growth of follicles (which contain eggs) in the ovaries.
Having low levels during the follicular phase is completely normal. The body is preparing to ovulate, and progesterone production doesn’t begin until after ovulation.
The Luteal Phase
After ovulation, levels begin to rise—averaging 25 mg every day. The luteal phase is the second half of your cycle, typically lasting around 12 to 14 days. During this time, progesterone helps thicken the uterine lining and creates a nourishing environment in case fertilization happens.
If you’re trying to conceive, this is the critical phase for implantation and early pregnancy support. Progesterone levels peak about 5 to 7 days after ovulation—right when implantation is most likely to occur.
If fertilization does not happen, the corpus luteum breaks down, levels drop, and your period begins.
Why Progesterone Matters When Trying to Conceive
For anyone on the TTC journey, progesterone isn’t just a hormone; it’s your body’s way of saying, ‘let’s make this pregnancy happen.’ It’s especially important during implantation and the early weeks of pregnancy.
Progesterone and Implantation
Progesterone helps transform the uterine lining into a soft, thick, nutrient-rich environment ideal for a fertilized egg to implant. Without sufficient levels, the lining may be too thin or unstable, making implantation difficult or unlikely.
Low levels can lead to a short luteal phase (known as luteal phase defect), which may not give the embryo enough time to implant successfully before menstruation starts.
Progesterone and Early Pregnancy
If implantation is successful and pregnancy begins, progesterone is crucial in supporting it. This hormone tells the uterus to stay relaxed and not contract, helping prevent miscarriage in early pregnancy. It also works with the immune system so the embryo isn’t rejected.
In early pregnancy, the corpus luteum continues making progesterone until the placenta takes over around 8–10 weeks.
What is PdG and How Does It Relate to Progesterone?
PdG stands for pregnanediol glucuronide, a substance your body makes after breaking down progesterone. While the hormone itself is measured in blood, PdG is what shows up in urine and what makes it possible to track using at-home PdG tests.
What does PdG test for?
PdG appears in urine only after ovulation, once progesterone levels rise. Testing PdG provides a non-invasive way to help determine if ovulation likely occurred and to assess whether your body is producing enough during the luteal phase to support implantation.
Premom’s sister brand, Easy@Home, offers PdG test strips that make it easy to track these hormone levels from the comfort of your home. Use the Premom app to scan your test and gain clearer insight into your cycle–helping you understand whether your body is supporting a healthy environment for pregnancy.
Can PdG testing tell me if ovulation was successful?
Yes. One of the main benefits of PdG testing is feeling more confident that ovulation occurred and that your body likely produced a healthy amount of progesterone in the days after. Sustained PdG levels for multiple days after ovulation indicate a strong likelihood of ovulation and sufficient luteal phase support.
Tools like PdG tests (used alongside LH or ovulation predictor kits) can give you a clearer picture of your fertile window and whether ovulation is happening consistently.
Signs and Symptoms of Progesterone
Your body often gives clues when hormone levels shift. Here’s how you might feel progesterone at work—or notice when it’s lacking.
Physical signs your progesterone is rising
When progesterone increases after ovulation, you might notice:
- Breast tenderness
- Higher basal body temperature (BBT)
- Changes in cervical mucus (creamy or sticky)
- Mild bloating or mood changes
- Better sleep or a calm feeling (this hormone has a calming effect)
How do you know if you have low progesterone?
Low progesterone may show up as:
- Spotting before your period
- Short luteal phase (less than 10 days)
- Trouble getting or staying pregnant
- Intense PMS (premenstrual syndrome) symptoms like irritability
If you suspect your levels may be low, speak to your doctor about testing via blood serum or urine (PdG test) and exploring treatment options.
Why would a woman have to take progesterone?
Doctors often prescribe it if your levels are low after ovulation or in early pregnancy. You might need progesterone support if:
- You’ve had recurrent pregnancy loss
- Your luteal phase is consistently short
- Your PdG or blood tests indicate low progesterone
- You’ve undergone fertility treatments like IVF or IUI
In TTC journeys, taking progesterone can help the uterine lining stay thick enough to support implantation and pregnancy. Numerous clinical studies have concluded that progesterone supplementation is associated with a decrease in the rate of miscarriage.
Common Questions Women Ask About Progesterone When TTC
Can progesterone cause weight gain or bloating?
Some women do report weight gain or bloating when taking progesterone supplements. These symptoms are usually due to water retention or slower digestion, which are common side effects of rising progesterone. However, not everyone experiences this. Weight changes are typically temporary and often resolve once your body adjusts or the supplement is stopped.
Interestingly, a 2011 study followed 765 menstrual cycles of 62 healthy women and concluded that progesterone was not significantly associated with bloating. In fact, the average peak day of bloating was the first day of their period. Learn more about weight gain and progesterone.
What’s the difference between estrogen and progesterone?
Estrogen builds up the uterine lining and helps with egg development before ovulation. Progesterone takes over after ovulation to maintain the lining and support implantation. Think of estrogen as preparing the house, and progesterone as keeping it ready for a guest (the embryo).
Do ovulation tests test for progesterone?
No, ovulation tests (also called OPKs) measure LH (luteinizing hormone), which surges before ovulation. They don’t tell you if ovulation actually happened or if progesterone rose afterward. To measure progesterone, you’d need a blood test or a PdG urine test, which checks if ovulation actually happened and if your body produced enough afterward.
What happens to progesterone after a positive pregnancy test?
If you get a positive pregnancy test, progesterone should continue to rise. The corpus luteum keeps producing it until the placenta takes over around 8 to 10 weeks of pregnancy.
If levels drop too soon, it may increase the risk of miscarriage, which is why some women are prescribed progesterone support during early pregnancy.
How to Track Fertility Hormones Naturally
Understanding your cycle starts with tracking. By using tools like OPKs and PdG tests, you can gain a clearer picture of your hormonal health and ovulation patterns.
Tracking ovulation and luteal phase in the Premom app
Your cycle gives you many clues about your fertility. Using the Premom app, you can log symptoms like cervical mucus, BBT, ovulation test results, and even PdG data to see your cycle patterns clearly.
The app helps you find your most fertile days, track how long your luteal phase is, and get insight into whether your progesterone levels may support implantation.
Using OPKs and PDG to understand your fertile window and ovulation better
Combining ovulation test tracking with PdG testing gives a fuller picture of your hormone health. OPKs tell you when your body is gearing up to ovulate. PdG tells you if ovulation likely happened and whether your progesterone levels increased afterward.
This dynamic duo can help you:
- Time sex in your fertile window
- Feel more confident that ovulation occurred
- Spot potential hormone imbalances sooner
FAQS About Progesterone
What is the main purpose of progesterone?
It helps to prepare the uterus for implantation and supports early pregnancy.
What does progesterone do during pregnancy?
It helps sustain a pregnancy by thickening and maintaining the uterine lining so the embryo can implant and grow. It helps relax the uterine muscles ot prevent early contractions and supports the development of the placenta in the first trimester.
How do I know if my progesterone is too low?
Signs of low progesterone may include a short luteal phase, spotting before your period, or trouble staying pregnant. You can check your levels through bloodwork or with at-home PdG tests, which may help you decide if it’s time to talk to your doctor.
References
Ku C.W., Allen J.C., Jr., Lek S.M., Chia M.L., Tan N.S., Tan T.C. Serum progesterone distribution in normal pregnancies compared to pregnancies complicated by threatened miscarriage from 5 to 13 weeks gestation: A prospective cohort study. BMC Pregnancy Childbirth. 2018;18:360. doi: 10.1186/s12884-018-2002-z.
Reed BG, Carr BR. The normal menstrual cycle and the control of ovulation. Endotext – NCBI Bookshelf. Published August 5, 2018. https://www.ncbi.nlm.nih.gov/books/NBK279054/
Tan TC, Ku CW, Kwek LK, et al. Novel approach using serum progesterone as a triage to guide management of patients with threatened miscarriage: a prospective cohort study. Scientific Reports. 2020;10(1). doi:10.1038/s41598-020-66155-x
White CP, Hitchcock CL, Vigna YM, Prior JC. Fluid Retention over the Menstrual Cycle: 1-Year Data from the Prospective Ovulation Cohort. Obstet Gynecol Int. 2011;2011:138451. doi:10.1155/2011/138451
