Urinary PdG (pregnanediol glucuronide) levels at or above 5 µg/mL, sustained for at least two consecutive days after ovulation, are associated with the hormonal conditions needed for a healthy early pregnancy. That threshold comes from ovulation-confirmation research rather than pregnancy-specific clinical guidelines, because PdG testing in pregnancy is still a relatively new area without the kind of standardized reference ranges that exist for serum progesterone. The distinction matters, and understanding what PdG can and cannot tell you during pregnancy requires knowing where the number comes from and how to interpret it in context.
What PdG Actually Measures
PdG is the main breakdown product of progesterone that your body excretes in urine. After your ovaries (and later, the placenta) produce progesterone, your liver processes it, and the resulting PdG ends up in your urine. Measuring PdG is an indirect way to gauge how much progesterone your body is making. Researchers have developed methods to measure PdG directly in urine samples, including dried urine spots, using advanced lab techniques that track this metabolite alongside other steroid markers.1PubMed. Direct measurement of pregnanediol 3-glucuronide (PDG) in dried urine spots by liquid chromatography-mass spectrometry to detect ovulation This is the science behind the at-home urine PdG tests that have become popular among people trying to conceive.
The appeal of PdG testing is convenience. A blood draw measures serum progesterone directly, but it requires a visit to a lab or clinic. PdG strips let you track the same hormone’s footprint from home, using first-morning urine. The tradeoff is precision: urine concentration varies with hydration, time of day, and kidney function, so the numbers are inherently noisier than a blood test.
The 5 µg/mL Threshold and Where It Comes From
Most at-home PdG test strips are calibrated around a 5 µg/mL cutoff. This number was established through ovulation-confirmation research, not pregnancy research. In a study using an FDA-cleared PdG monitoring system, researchers found that PdG levels sustained above 5 µg/mL during the 7 to 10 days after the LH surge reliably confirmed that ovulation had occurred. In 37 out of 38 ovulatory cycles studied, PdG reached above that mark at least once in that window. Interestingly, the same study also noted that ovulation could be confirmed with PdG values as low as 2.5 µg/mL when following the rise pattern from baseline.2PubMed Central. Complete Cycle Mapping Using a Quantitative At-Home Hormone Monitoring System in Prediction of Fertile Days, Confirmation of Ovulation, and Screening for Ovulation Issues Preventing Conception
A separate evaluation tested two different PdG strip sensitivities: 5 µg/mL and 7 µg/mL. The more sensitive strips detected positive PdG in about 82% of confirmed ovulatory cycles, while the 7 µg/mL strips only caught about 59%. The positive readings typically showed up 2 to 10 days after the LH surge, most commonly on days 4 and 5.3Frontiers in Public Health. Pilot Evaluation of a New Urine Progesterone Test to Confirm Ovulation in Women Using a Fertility Monitor This tells you something practical: a higher cutoff catches fewer real positives, and the 5 µg/mL threshold is already a balance between sensitivity and specificity.
When people apply this threshold to early pregnancy, they are extending the ovulation data into new territory. The logic is reasonable — if progesterone was adequate to prepare the uterine lining for implantation, that is a good sign for the embryo’s early environment. But no clinical body has published a validated PdG reference range specifically for weeks 4 through 12 of pregnancy. You are working with the best available proxy, not a pregnancy-specific diagnostic standard.
PdG Patterns and Miscarriage Risk
The most striking data on PdG and pregnancy outcomes comes from a study of 172 women, 54 of whom became pregnant. A “positive cycle” was defined as one where PdG levels stayed at or above 5 µg/mL for at least two days during the luteal phase. Among women who conceived during a positive cycle, the miscarriage rate was 14.3%. Among those who conceived during a negative PdG cycle, the miscarriage rate was 89.5%.4Obstetrics and Gynecology Research. The Predictive Value of Urinary Progesterone Metabolite PdG Testing in Pregnancy Outcomes That difference is enormous, and it is the number most people encounter when researching this topic.
The connection between adequate progesterone and pregnancy survival is well supported by broader evidence. A scoping review examining 23 studies found a consistent positive relationship between progesterone deficiency and first-trimester miscarriage. The risk increased further when low progesterone was combined with declines in other hormones.5PubMed Central. Exploring Progesterone Deficiency in First-Trimester Miscarriage and the Impact of Hormone Therapy on Foetal Development: A Scoping Review Progesterone prepares the uterine lining for implantation and helps maintain the pregnancy environment in the critical early weeks.6Research Square. The predictive value of urinary Progesterone metabolite PdG testing in pregnancy outcomes
A word of caution about interpreting these numbers: the 89.5% miscarriage rate in negative PdG cycles does not mean that a single low PdG reading dooms a pregnancy. That figure reflects cycles where PdG never sustained above threshold, suggesting the corpus luteum was not producing enough progesterone overall. A one-off low reading on a single morning could reflect dilute urine, testing at the wrong time, or normal day-to-day variation rather than a genuine hormonal problem.
Why PdG Levels Change as Pregnancy Progresses
In the first several weeks of pregnancy, your corpus luteum (the structure left behind on the ovary after ovulation) is the main source of progesterone. Around weeks 7 to 9, the placenta gradually takes over progesterone production in what researchers call the luteal-placental shift. In naturally conceived pregnancies, the ratio of progesterone to another ovarian hormone (17-OHP) rises between weeks 4 and 9, reflecting this handoff.7PubMed. Delayed luteo-placental shift of progesterone production in IVF pregnancy
This transition means that PdG levels are not static in early pregnancy. They typically rise as the placenta matures and begins pumping out progressively more progesterone. If you are tracking PdG at home, you might notice readings climbing from week to week during the first trimester. A temporary dip around weeks 7 to 8 is sometimes reported anecdotally as the two sources of progesterone overlap, though this varies widely between individuals.
In IVF pregnancies, researchers found that this shift can be delayed, with the placenta taking longer to assume full progesterone production.7PubMed. Delayed luteo-placental shift of progesterone production in IVF pregnancy This is one reason IVF patients are often prescribed progesterone supplementation through the first trimester: the corpus luteum may not function the same way after ovarian stimulation, and the placenta needs time to catch up.
Hydration and the Reliability Problem
One of the biggest practical challenges with urine PdG testing is that your hydration level directly affects the concentration of PdG in your sample. Drink a lot of water before bed, and your first-morning urine is more dilute, potentially dragging your PdG reading below threshold even if your body is producing plenty of progesterone. This is not a hypothetical concern — it is a known measurement issue that researchers have studied specifically.
Research comparing different ways to correct for hydration found that raw urine concentration without any correction is the least reliable approach. Adjusting for creatinine (a waste product excreted at a relatively constant rate) improves accuracy, and measuring actual excretion rates over a timed collection is more reliable still.8Open Health. Expressing the quantity of urinary analytes: a discussion of some issues arising from the monitoring of the menstrual cycle Unfortunately, at-home PdG strips do not correct for creatinine. They measure raw concentration in a spot sample, which means they are vulnerable to hydration-related noise.
If you are using at-home PdG strips during early pregnancy, consistency helps. Testing with your first-morning urine, avoiding unusually large fluid intake the night before, and looking at multi-day patterns rather than single readings all reduce the chance that hydration is throwing off your results. A single reading below 5 µg/mL is less informative than a pattern of sustained low readings over several days.
Serum Progesterone Versus Urinary PdG
Your doctor is far more likely to order a serum progesterone blood test than to track urinary PdG. The two measurements are related but not interchangeable, and the clinical evidence base is much deeper for serum progesterone.
One commonly cited clinical threshold is a serum progesterone level of 20 nmol/L (about 6.2 ng/mL). The Royal College of Obstetricians and Gynaecologists has suggested that levels below this mark predict a non-viable pregnancy with about 93% sensitivity and 94% specificity in women with symptoms like bleeding or pain and inconclusive ultrasound findings. However, a meta-analysis examining the same underlying data challenged this, noting that no single progesterone value can confidently rule in or rule out a normal viable pregnancy.9PubMed Central. Accuracy of single progesterone test to predict early pregnancy outcome in women with pain or bleeding: meta-analysis of cohort studies The evidence is genuinely conflicted on how much weight to put on a single serum progesterone number, which should make you even more cautious about drawing strong conclusions from a single urine PdG reading.
Serum progesterone in early pregnancy generally ranges from about 10 to 44 ng/mL during the first trimester in viable pregnancies, though individual variation is wide. Because PdG in urine reflects progesterone after liver metabolism, kidney filtration, and dilution, the absolute numbers do not translate directly. You cannot take a PdG reading and convert it to a serum progesterone equivalent with any real precision. They track the same hormone, but through very different lenses.
Does Progesterone Supplementation Help?
If your PdG levels are running low, the natural question is whether adding progesterone supplementation can rescue the situation. The answer is more complicated than you might expect.
The largest randomized trial on this question enrolled over 4,000 women experiencing vaginal bleeding in early pregnancy. Women who received vaginal progesterone had a live birth rate of 75%, compared to 72% in the placebo group. That three-percentage-point difference did not reach statistical significance.10PubMed. A Randomized Trial of Progesterone in Women with Bleeding in Early Pregnancy In other words, across the full group of women with early pregnancy bleeding, progesterone supplementation did not meaningfully improve outcomes.
That does not mean supplementation never helps. The same trial found a trend toward benefit in women with a history of recurrent miscarriages, and some clinicians prescribe progesterone for patients with documented low levels, particularly those undergoing IVF or with a history of luteal phase deficiency. The scoping review on progesterone deficiency and miscarriage also noted that hormone therapy was being studied as an intervention, though the overall picture remains mixed.5PubMed Central. Exploring Progesterone Deficiency in First-Trimester Miscarriage and the Impact of Hormone Therapy on Foetal Development: A Scoping Review The frustrating reality is that low progesterone sometimes causes a miscarriage, and sometimes low progesterone is a consequence of a pregnancy that was already failing for other reasons, like a chromosomal abnormality. Supplementation can address the first scenario but not the second.
One practical note: if you are taking progesterone supplements (vaginal, oral, or injection), your PdG levels will reflect both your body’s natural production and the exogenous hormone. This can make at-home PdG readings harder to interpret, since you may see elevated readings that reflect the supplement rather than your body’s own output. Your provider will likely rely on serum progesterone or clinical assessment rather than urinary PdG tracking in this situation.
When a Low PdG Reading Warrants a Call to Your Doctor
At-home PdG testing sits in an awkward spot between consumer wellness tracking and clinical diagnostics. The strips are cleared for ovulation confirmation, not pregnancy monitoring. That said, patterns in your PdG readings can provide useful early information that you can bring to a provider.
Situations that warrant a conversation with your doctor include consistently low PdG readings (below 5 µg/mL on multiple mornings) during the luteal phase of a conception cycle, a pattern of declining PdG after previously elevated readings in early pregnancy, or low PdG paired with symptoms like cramping or spotting. None of these is diagnostic on its own, but they give your provider a reason to check serum progesterone, order an ultrasound, or consider supplementation.
What you should avoid is panic over a single low reading. Urine concentration fluctuates. Test strips have margins of error. Even serum progesterone, the gold-standard blood test, has enough variability that clinicians are cautioned against making major decisions based on a single draw.9PubMed Central. Accuracy of single progesterone test to predict early pregnancy outcome in women with pain or bleeding: meta-analysis of cohort studies A pattern matters; a snapshot usually does not.
The Long Road From Lab Curiosity to Home Test Strip
Measuring urinary pregnanediol as a marker of pregnancy is not a new idea. The earliest work dates to 1937, when researchers first described how pregnanediol excretion tracked with pregnancy. Through the 1940s, multiple groups tried to turn this into a practical pregnancy test, isolating the PdG compound from 24-hour urine collections. The results were promising, but the methods were slow and technically demanding.11Journal of Endocrinology. URINARY PREGNANEDIOL ESTIMATION AS A TEST FOR PREGNANCY It took decades of advances in immunoassay technology and, more recently, lateral-flow strip design for this measurement to become something a person could do in their bathroom in five minutes.
The fact that the science has nearly a century of history behind it is both reassuring and humbling. Researchers have known for a long time that urinary progesterone metabolites track with pregnancy viability. What has lagged behind is the ability to measure them cheaply, quickly, and accurately enough for consumer use, and to generate the kind of large-scale clinical validation data that would allow professional bodies to issue specific PdG reference ranges for pregnancy monitoring. That validation work is underway, but for now, the 5 µg/mL threshold remains an ovulation-derived benchmark that happens to correlate well with early pregnancy outcomes rather than a formally validated pregnancy diagnostic cutoff.