A PdG test is a urine test that confirms whether ovulation actually occurred. It measures pregnanediol glucuronide (PdG), which is the form progesterone takes after your body processes it and sends it to your urine. While most people are familiar with LH (ovulation predictor) tests that tell you ovulation is *about* to happen, a PdG test tells you it already *did* happen, filling a gap that LH strips alone can’t cover.
How PdG Relates to Progesterone
After you ovulate, the follicle that released your egg transforms into a small structure that pumps out progesterone. This hormone is essential for preparing the uterine lining for a potential pregnancy and supporting early gestation. Your body metabolizes progesterone in the liver, and the end product, PdG, gets filtered out through your kidneys and into your urine.
Traditionally, confirming ovulation meant a blood draw at a doctor’s office to check serum progesterone levels, typically scheduled around day 21 of your cycle. A PdG test does essentially the same thing at home with a urine sample. Research from Oxford Academic found that urinary PdG correlates with serum progesterone at an R² of 0.95, meaning the urine measurement tracks the blood value almost perfectly. In the same study, every single case where blood work confirmed ovulation, the urinary PdG reading confirmed it too.
First-morning urine tends to give the most reliable results. The same study found that first-morning samples actually correlated better with serum hormone levels than samples that were adjusted for urine concentration, so you don’t need to worry about how diluted your urine is as long as you test first thing.
Prediction vs. Confirmation
LH tests and PdG tests serve different purposes, and understanding the distinction matters if you’re tracking fertility. An LH test detects the surge in luteinizing hormone that happens 12 to 48 hours before ovulation. It tells you the window is opening. But an LH surge doesn’t guarantee that an egg was actually released. You can have a surge without ovulation, a situation called an anovulatory cycle.
A PdG test picks up where the LH test leaves off. Rising PdG levels confirm that the post-ovulation process is underway and progesterone is being produced. This is particularly useful if you’ve been trying to conceive for several months without success, because it can reveal whether the issue is ovulation itself or something else entirely. It’s also helpful for people with irregular cycles who may not always ovulate consistently.
What Counts as a Positive Result
A single elevated PdG reading isn’t enough. The key is a sustained rise over multiple days, because a brief spike can sometimes be misleading. PdG levels above 5 micrograms per milliliter for three consecutive days is the general threshold that indicates ovulation occurred successfully.
The timing of that rise varies from person to person. Some people see PdG climb within a day or two after ovulation. Others may not see a consistent rise for three to four days, and in some cases it can take seven days or more. This variation is normal and doesn’t necessarily mean anything is wrong. It simply means you need to test over several days rather than relying on a single reading.
When and How to Test
PdG testing works best when you pair it with an LH test so you know roughly when ovulation happened. The general approach is to start testing five days after you get a positive result on an ovulation predictor kit, then continue testing daily until you get a positive PdG result before your next period. Testing with first-morning urine gives the most accurate reading.
If you never see a sustained rise in PdG across multiple cycles, that’s useful information. It could suggest you’re having anovulatory cycles (where your body goes through the motions but doesn’t release an egg) or that your progesterone levels after ovulation are lower than expected. Low post-ovulation progesterone, sometimes called a luteal phase defect, can make it harder for a fertilized egg to implant.
Who Benefits Most From PdG Testing
If you’re casually tracking your cycle and getting regular periods, an LH test alone may be all you need. PdG testing adds the most value in specific situations: when you’ve been trying to conceive for several months without success, when your cycles are irregular and you’re not sure ovulation is happening, or when you’ve gotten positive LH tests but suspect you may not actually be ovulating. It’s also useful for people who want a more complete picture of their hormonal pattern each cycle without repeated trips to a lab for blood work.
Several at-home fertility monitors now integrate PdG alongside LH and estrogen readings to map your full cycle. These devices use test strips that you dip in a urine sample and then scan with a phone app, giving you a hormone curve over time rather than a single data point. The multi-day tracking approach aligns with how PdG naturally behaves: it’s not about one number on one day, but about watching the pattern build across your luteal phase.