PdG (pregnanediol glucuronide) is the form progesterone takes after your body breaks it down and sends it into your urine. In fertility tracking, measuring PdG lets you confirm that ovulation actually happened and that your body produced enough progesterone afterward to support a potential pregnancy. While LH tests predict ovulation is coming, PdG tests tell you it already occurred.
How PdG Relates to Progesterone
After ovulation, the empty follicle left behind on the ovary transforms into a temporary structure that pumps out progesterone. This progesterone thickens the uterine lining, making it receptive to a fertilized egg. Your liver then metabolizes progesterone, and the main byproduct, PdG, is filtered out through your kidneys and into your urine.
Because PdG is progesterone’s primary metabolite, its concentration in urine closely mirrors what’s happening in your blood. Research comparing urinary PdG to blood progesterone levels found a correlation of 0.95, meaning the two track almost in lockstep. In every case where blood values confirmed ovulation, urinary PdG values confirmed it too. This tight relationship is what makes at-home urine testing a practical alternative to a blood draw at a clinic.
The 5 µg/mL Threshold
The number that matters for PdG testing is 5 µg/mL. Studies using ultrasound-confirmed ovulation found that when urinary PdG stays above this level for three consecutive days after the LH surge, ovulation is confirmed with 100% specificity, meaning zero false positives. A blood progesterone level above 3 ng/mL is the traditional clinical benchmark for confirming ovulation, and the 5 µg/mL urinary PdG threshold corresponds well to that value.
One positive test isn’t enough on its own. Progesterone (and therefore PdG) can spike briefly without sustaining the levels needed for implantation. Three consecutive days above threshold is the standard that research supports.
Why “Successful Ovulation” Means More Than Just Ovulating
You can ovulate and still have a cycle that doesn’t give a fertilized egg a real chance to implant. A “successful ovulation” in PdG terms means the egg was released and PdG levels stayed elevated through the implantation window, roughly 7 to 10 days after peak fertility. In one study tracking 40 menstrual cycles, only 22 showed PdG sustained above 5 µg/mL for at least three of four testing days during that window. The remaining cycles either had weak progesterone output or levels that dropped too early.
When PdG falls below 5 µg/mL on two or more of those testing days, it flags possible ovulatory dysfunction. This doesn’t necessarily mean you didn’t ovulate at all. It may mean your body didn’t produce enough progesterone afterward to adequately prepare the uterine lining.
Low PdG and Luteal Phase Problems
Consistently low PdG levels point toward a condition called luteal phase deficiency, where progesterone output after ovulation is too low or drops off too quickly. The luteal phase is the stretch of time between ovulation and the start of your next period, and it typically needs to last at least 9 days for the uterine lining to develop enough to support implantation.
Signs that may accompany luteal phase deficiency include a short gap (fewer than 9 days) between ovulation and your period, spotting that starts several days before your period with no other explanation, and irregular cycles. The condition has been linked to difficulty conceiving and recurrent pregnancy loss. Tracking PdG over several cycles can help you and a healthcare provider identify this pattern before investing months in timed intercourse or other interventions that assume progesterone levels are fine.
PdG Tests vs. LH Tests
LH (luteinizing hormone) tests and PdG tests answer two different questions. An LH test detects the hormonal surge that triggers the release of an egg, typically about 24 hours before ovulation. It tells you the fertile window is open right now. A PdG test, taken days later, tells you the window closed successfully and your body shifted into the progesterone-dominant phase needed for implantation.
Using both together gives a more complete picture of your cycle. LH confirms the attempt to ovulate; PdG confirms it worked and that the hormonal environment afterward is adequate. Many people who have been tracking only LH find that adding PdG testing reveals cycle issues that were previously invisible.
How At-Home PdG Tests Perform
At-home PdG test strips and monitors have been validated in clinical studies with strong results. Specificity for confirming ovulation was 100% across multiple testing scenarios, meaning the tests did not falsely tell anyone they had ovulated when they hadn’t. Sensitivity ranged from 85% to 95%, depending on the method used to identify peak fertility beforehand. The highest sensitivity (95%) came from testing a single PdG strip on the third day after the first positive LH test.
For the most reliable confirmation, the standard protocol is to get a positive LH result first, then begin testing PdG a few days later and look for three consecutive days above threshold. Testing during the implantation window (7 to 10 days post-peak fertility) gives the most clinically meaningful information, since it reveals whether progesterone stayed elevated long enough to matter.
Hydration Can Skew Your Results
Because PdG is measured in urine, how dilute your sample is directly affects the reading. Research found that when urine was concentrated enough (a specific gravity of 1.015 or higher), PdG and blood progesterone correlated strongly. But when urine was more dilute than that, the correlation fell apart. In practical terms, this means drinking large amounts of water before testing can produce a falsely low PdG reading.
First morning urine tends to be the most concentrated and gives the most reliable results. If you’re testing later in the day, avoid chugging water in the hour or two beforehand. Some monitors measure urine concentration alongside PdG to adjust for dilution, but if you’re using simple test strips, sample concentration is entirely on you to manage.