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Low Progesterone and Pregnancy: How Progesterone Affects Your Fertility

by Katie Melville, Ph.D.

Published on

low progesterone and pregnancy

Low progesterone can cause or contribute to infertility and miscarriages. Read on to learn progesterone’s role in a woman’s cycle, how important it is for pregnancy, and what you can do if you suspect low progesterone.

True to its name, progesterone (literally meaning “pro-gestation”) helps a woman get pregnant and stay pregnant. If your body isn’t making enough, then you might suffer from recurrent miscarriages or not be able to get pregnant in the first place. Although many factors contribute to a woman’s fertility, this article will discuss the importance of progesterone, how to know if you might have low progesterone, and what you can do about it.

If you’re struggling with your fertility, low progesterone could be a contributing factor. Check out this article from Katie Melville to learn more about the important role progesterone plays and what you can do if you suspect low progesterone. #functionalmedicine #wellness

The Purposes of Progesterone

Progesterone is important in both a woman’s normal menstrual cycle and during pregnancy. Low progesterone can be associated with repeat miscarriages, infertility, postpartum depression, and even conditions like low bone mass and higher cardiovascular risk. (1, 2, 3, 4)

Progesterone in the Luteal Phase

The luteal phase of a women’s cycle begins at ovulation and lasts until the next period begins. Healthy women should have a luteal phase that lasts 11 to 16 days—and progesterone plays an important role in that length. (5)

At ovulation, the dominant follicle releases an egg that slowly travels down the fallopian tube to the uterus, hoping to be fertilized. The now ruptured follicle becomes a tiny, temporary endocrine organ called the corpus luteum, which secretes hormones including progesterone to help prepare the endometrium for an embryo to attach. If the egg isn’t fertilized, progesterone drops, triggering the endometrial lining to shed in menstruation.

If the egg is fertilized, the resulting embryo will take approximately seven to 10 days to travel down the fallopian tube and implant into the uterine wall. However, if the corpus luteum doesn’t generate enough progesterone, then the uterine lining sheds too soon, never allowing the embryo to implant well or at all. (6) Without enough progesterone, the woman will experience an apparently normal period and may never know she was pregnant.

Progesterone during Pregnancy

If sperm does fertilize the egg, the resulting embryo should begin producing human chorionic gonadotropin (hCG), the pregnancy hormone. hCG triggers the corpus luteum to continue producing progesterone to keep the uterine lining from shedding. The corpus luteum provides the necessary progesterone until the placenta can take over at around seven to nine weeks of pregnancy. (7)

During pregnancy, progesterone serves several functions, including: (8)

  • Altering the maternal immune response and suppressing inflammation to prevent the immune system from rejecting the “foreign” tissue
  • Reducing uterine contractility to prevent the uterus from expelling the fetus
  • Improving the circulation between the mom and fetus

If not enough progesterone is produced by the corpus luteum after implantation, or if not enough progesterone is produced by the placenta after seven to nine weeks, then a miscarriage is likely. Studies have shown that lower progesterone levels during the first trimester were associated with a higher risk of miscarriage. (9, 10)

Despite this correlation, measuring progesterone levels during early pregnancy is still not a routine practice in obstetrician-gynecologist offices.

Low Progesterone and Luteal Phase Defect

Low progesterone and luteal phase defect (LPD) are often used interchangeably, but that’s not entirely accurate. Although its characterization has evolved over time, LPD is best described as an abnormality in endometrial development that can result in infertility or miscarriage. Common symptoms of LPD include: (11, 12)

  • A luteal phase (the time from ovulation to the next period) that lasts 10 days or less
  • Serum progesterone levels lower than 5 ng/mL at six to eight days after ovulation
  • Spotting for several days before a period starts

Low progesterone is probably the most common cause of LPD, but LPD does not always present with low progesterone. In these cases, the corpus luteum could be secreting enough progesterone, but for some reason the endometrium isn’t responding properly to it. In a study comparing endometrial tissue, women with unexplained infertility had fewer progesterone receptors in their endometrium compared to parous women. (13) With fewer progesterone receptors, “normal” progesterone levels still might not be enough to develop a healthy endometrium and sustain a pregnancy.

How Conventional Medicine Gets Progesterone Testing Wrong

If you have a short luteal phase, spotting before a period, or fertility issues, getting your progesterone levels checked seems like a no-brainer place to start. Unfortunately, many medical offices won’t even consider testing a woman’s cyclic hormone levels until after three miscarriages or at least one year of unsuccessfully trying to conceive. And, even if they do agree to run hormone panels, they often will measure progesterone at the wrong time.

Progesterone should peak midway through the luteal phase, around six to eight days after ovulation. (14) In a clockwork 28-day cycle with a 14-day luteal phase, day 21 falls directly in the middle of the luteal phase. This is why day 21 is standard for measuring luteal phase serum progesterone. However, so few women exhibit these clockwork cycles. For example, if you generally have 32-day cycles and a 12-day luteal phase, your ovulation day is around day 20. Progesterone in this cycle won’t peak until around day 26, and measuring at day 21 won’t be able to tell you if you do or do not have enough progesterone that cycle.

The midpoint of the luteal phase differs from woman to woman and even from cycle to cycle in the same woman. The best way to correctly estimate ovulation day is to track your cycles with an effective fertility awareness-based method (FABM) of birth control. By tracking basal body temperature, cervical mucus, and even urine hormone metabolite levels, FABMs empower women to understand their body’s signs of health and fertility. In an FABM, the 21-day progesterone test is best taken six or seven days after identifying the “peak” day in your cycle according to the FABM you use, regardless of what absolute “cycle day” that falls on.

How to Measure Your Progesterone at Home

As an alternative to serum testing that requires doctor visits and lab orders, you can now measure progesterone levels at home with Proov test strips. Instead of measuring progesterone, these U.S. Food and Drug Administration-approved kits measure pregnanediol-3-glucuronide (PdG), a urine metabolite of progesterone that correlates well with serum progesterone levels. (15)

Similar to a pregnancy test, Proov should be done with first-morning urine. Unlike a pregnancy test that’s positive when the test line appears, the Proov test is positive when the test line disappears. Positive indicates sufficient progesterone. If you have enough progesterone post-ovulation, then you should get a positive progesterone test on days 7, 8, 9, and 10 after the peak day as determined through an FABM.

If you never get a positive reading, then you might not be ovulating at all. Progesterone rises only after a successful ovulation. If you get a positive reading on some of the days 7 through 10 but not all 4, that indicates that your body isn’t producing enough progesterone after ovulation.

You Have Low Progesterone—Now What?

If you are having trouble getting pregnant and have confirmed low progesterone, a bioidentical progesterone supplement may help—but not always. When hormone levels are out of balance, it’s likely that other underlying issues exist and it’s important to address those issues.

Working with a Functional Medicine practitioner could help identify any other health problems that could be contributing to infertility, such as:

Often, the conventional medical approach to infertility doesn’t take underlying conditions like these into account. Functional Medicine, however, is a systems-based approach to care that’s focused on uncovering and treating the root cause of any condition so patients can truly heal. If you’re a licensed medical practitioner and are looking for a better way to help your patients, Functional Medicine training may be the right path forward for you. Find out how the ADAPT Practitioner Training Program can help you embrace an investigative, holistic, patient-centered approach to healthcare.

Bioidentical Progesterone Supplementation

If low progesterone is the only discernible issue, then bioidentical supplementation may be a good option, often given as a vaginal suppository. Bioidentical progesterone is routinely used in artificial reproductive technology and is generally considered safe for both the mom and fetus. (21) Importantly, bioidentical progesterone is not the same as the synthetic progesterones like progestins found in hormonal birth control pills, which are associated with many more side effects, including weight gain, headache, acne, and possibly even side effects to the fetus. (22)

Studies show that bioidentical progesterone supplementation can help women with a history of recurrent miscarriage when taken early enough in the pregnancy. In women with unexplained recurrent miscarriage, progesterone supplementation beginning at five to six weeks of pregnancy did not yield better pregnancy outcomes when compared to placebo. (23) But if a woman has low progesterone, waiting until six weeks into the pregnancy may be too late. Progesterone helps build up the endometrium to allow an embryo to implant, and helps sustain a pregnancy after implantation. At six weeks pregnant, implantation has happened weeks ago, possibly into an already progesterone-depleted uterus.

However, when women with a history of recurrent miscarriage began progesterone supplementation just three days after ovulation instead of waiting until after a positive pregnancy test, pregnancy outcomes were improved versus placebo. (24) When taken early, progesterone levels are replete well before implantation, preparing the endometrium for implantation and the body for pregnancy.

Be Your Own Health Advocate

If you’ve taken an at-home progesterone test and discovered that your progesterone doesn’t rise enough after ovulation, take that information to your doctor. Start a conversation about your concerns, and come prepared. Show them the studies where progesterone supplementation, when taken early enough, has helped, and discuss whether it can be an option for you. Be your own health advocate.

Katie Melville
Katie Melville, Ph.D.

Katie Melville earned a Ph.D. in Biomedical Engineering from Cornell University, where she studied the mechanisms of bone formation and resorption. In particular, she elucidated the effects of sex hormones and their receptors on bone mass and architecture. She also researched estrogen's role in bone's response to mechanical loading. She has co-authored several peer-reviewed research papers, written book chapters, and has presented at national conferences, including those held by the Orthopaedic Research Society and the American Society for Bone and Mineral Research.

Her interest in Ancestral Health and Functional Medicine began over a decade ago, when she started following Chris Kresser's articles and podcasts. Over the years, she has made significant changes to her family’s lifestyle, including adopting a Paleo diet template, installing a reverse-osmosis water filter, and incorporating a standing desk into her office space.

Since 2016, she has been honored to be a writer and researcher for Chris Kresser and Kresser Institute, relying on peer-reviewed literature and incorporating Chris's clinic experiences into her articles. Katie strives to understand the current knowledge surrounding human chronic disease, and enjoys digging deep into the scientific literature. She believes the future of healthcare lies in functional medicine.

Katie has also written for Natural Womanhood, a popular website that shares the benefits of fertility tracking and using natural, fertility awareness-based methods of birth control. For continued education, Katie has completed online courses from Stanford on scientific writing and how to critically interpret clinical trials.

Professionally, Katie works for Recruitomics Biotalent Consulting as a Scientific Recruiter for start-up biotech companies in the Boston area. Being in this role exposes her to the latest technological and medical


She lives near Boston with her husband and 3 young children, and she enjoys powerlifting and cooking in her spare time.

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