| "Helping women track their ovulation in a smarter way" | 
You’ve been watching your LH climb. Now you’re wondering when to take a PdG test so the result actually tells you something.
A study published in October 2026 in Frontiers in Endocrinology suggests testing PdG about 6 to 9 days after LH starts to surge. The researchers counted from the first day a woman’s LH reached a set level on a lab test. In the 243 ultrasound-tracked cycles where LH reached that level, PdG tested in that window gave the same result as ultrasound timing about 74% to 82% of the time.
That’s useful to know, because most PdG timing advice so far has come from expert opinion and test makers, not a direct check against ultrasound, as the authors point out. Here’s what the researchers tested, what they found, and what it could mean for you if you’re tracking at home.
Key takeaways
- The timing: About 6 to 9 days after LH starts to surge is when PdG testing lined up closely with ultrasound in this study, agreeing in about 74% to 82% of cycles.
- Why LH works as a guide: The day LH first hit the study’s set level usually fell right on ovulation day, and within a day of it in 70% of cycles.
- Numbers help: The method relied on reading LH as a number each day. The authors say it may not work the same way with line-only ovulation tests.
- One test isn’t the whole story: A single PdG result in this window isn’t enough to judge how your luteal phase is doing, the authors say.
What did the 2026 PdG timing study look at?
The question was simple. If you can’t get an ultrasound, can you use your LH to figure out when to test PdG?
Ultrasound is how researchers watch ovulation happen. A scan shows the follicle releasing its egg. But it means repeat clinic visits, which isn’t realistic for most people trying to conceive at home.
So a team led by Rene Leiva at the University of Ottawa, with Rene Ecochard and Jonathan Yang, went back to an older European data set. Between 1996 and 1997, 102 women at eight natural family planning clinics in France, Italy, Germany, Belgium, and Spain collected a urine sample each morning and had ultrasounds to see when they ovulated.
Their LH and PdG were measured in a lab. That gave the researchers two ways to count the days after ovulation: one from the ultrasound and one from LH. They compared PdG results 6, 7, 8, and 9 days later using each method to see how often the two agreed. In total, 283 cycles were included.
They picked days 6 to 9 because that’s the middle of the luteal phase, the stretch after ovulation when progesterone is usually at its highest. That lines up with an earlier ultrasound study, which found urinary PdG peaked a median of 7.5 days after ovulation. They didn’t study implantation or pregnancy, only timing.
When should you test PdG after your LH surge?
In this study, about 6 to 9 days after LH starts to surge.
To be specific, the researchers started counting on the first day LH reached 15 mIU/mL on their lab test. For the typical woman in the study, that day landed right on ovulation day, and it was within one day of it in 70% of cycles.
From there, PdG tested 6 to 9 days later gave the same result as ultrasound-timed testing in about three out of four cycles, sometimes more. No single day stood out as clearly better, so it’s a window, not one magic day.
Here’s how often PdG timed from LH agreed with PdG timed from the ultrasound ovulation day.
| What they compared | What they found | What it means |
|---|---|---|
| The day LH hit the study’s set level vs. ovulation day on ultrasound | Usually the same day. Within 1 day in 70.0% of cycles, within 2 days in 80.7%. | LH, read as a number, can stand in for ultrasound when timing PdG |
| PdG tested 6 days later | Agreed with ultrasound timing in 75.3% of cycles | Agreement held across the window |
| PdG tested 7 days later | 77.9% | Agreement held across the window |
| PdG tested 8 days later | 74.3% | Agreement held across the window |
| PdG tested 9 days later | 82.2%, the highest of the four | Not formally tested against the other days |
| Is one day better than the rest? | No single day stood out | Think of 6 to 9 days as a window, not one target day |
“Agreed” means both tests landed on the same side of the study’s PdG cutoff (15 µg/mL). These numbers come from lab testing of samples collected in 1996 and 1997. No home test was used.
A quick note on 15 mIU/mL. It’s a number from a lab machine, not a home test strip. Home LH tests use different chemistry, and the authors are clear that the numbers don’t carry over. If your app shows an LH reading of 15, it doesn’t mean the same thing as 15 in this study. What does carry over is the idea: time your PdG test from what your own LH is doing that cycle, not from a calendar date.
Should you count PdG days from the LH surge or the LH peak?
In this study, counting from early in the surge lined up with ultrasound a little more often than counting from the peak.
Your LH peak is your highest reading of the cycle, usually the darkest test line. It’s a great marker for timing sex. The catch for PdG timing is that you only know it was the peak once your LH starts coming back down. You can spot the day LH first crosses a set level as it happens.
Counting from the peak still worked. PdG 6 to 9 days after the peak agreed with ultrasound in 71.5% to 76.6% of cycles. That’s a little lower, though the researchers didn’t formally compare the two.
Higher LH levels lined up a bit more closely with ultrasound, but many cycles didn’t get that high. 243 cycles reached 15, while only 164 reached 30. That’s why the authors went with 15 as a practical middle ground.
“One of the most common worries I hear is a negative PdG test just a day or two after a positive ovulation test, and that’s usually a timing issue, not a progesterone problem. Progesterone takes several days after ovulation to build up, so give PdG about a week from when your LH starts rising before you read much into the result,” says Dr. Patti Haebe, NMD, Premom’s Senior Medical Advisor.
Why track LH and PdG together when trying to conceive?
LH and PdG answer two different questions. LH tests look ahead: a rising LH suggests ovulation is coming, so you can plan your best days to try. PdG tests look back: a positive PdG suggests you likely ovulated, and testing over the following days shows you what’s happening in your luteal phase, something LH can’t tell you.
This study also shows why reading LH as a number matters. The whole method depended on seeing LH as a daily value, not a yes or no line. When your LH is tracked as a number and drawn as a curve, a rise is easier to see, especially if your surges tend to be quick, drawn out, or come in two waves.
Put both on one chart and your cycle starts to tell a story. LH climbs, ovulation likely follows, then PdG and your temperature shift in the days after. And if PdG doesn’t turn positive or your luteal phase looks short, you’ve got something concrete to show your doctor, not just a feeling that something’s off.
Why did researchers use 15 µg/mL for PdG instead of 5?
If you’ve read about PdG before, you’ve probably seen 5 µg/mL. The two numbers answer different questions.
Think of 5 as a “did it go up?” number. It shows PdG has risen from its low level before ovulation, which suggests you likely ovulated.
Think of 15 as a “how high is it now?” number. In this study, the typical PdG level 6 to 9 days after ovulation was about 14 to 16 µg/mL, and the authors note that other studies have found similar levels, around 14 to 19. So 15 sits right around what’s common in the middle of the luteal phase.
The researchers also tried 5, 10, and 20. Lower cutoffs were better at agreeing on positive results, higher ones at agreeing on negatives, and 15 landed in the middle.
One thing 15 isn’t: a pass or fail grade for your luteal phase. The authors say a result above or below it doesn’t tell you how your luteal phase is working. PdG levels also vary a lot from person to person. Six days after ovulation, levels in this study ranged from under 2 to 65 µg/mL.
This study didn’t look at any home PdG test, so it can’t tell you how a strip performs at either number. Your test’s instructions explain what its result means.
How is urine PdG different from a blood progesterone test?
Progesterone is released in pulses, so the level in your blood can go up and down over the course of a day. A blood test catches it at one moment. PdG in your first morning urine reflects the progesterone your body processed over the hours you held it overnight, so it’s more like an overnight summary.
They measure different things in different ways. This study didn’t include any blood tests, so it can’t say how its urine numbers compare with blood levels, and it doesn’t say one test is better than the other.
How do you time a PdG test at home?
Here’s how to put this research to work if you’re tracking at home.
- Test LH once or twice a day between 10 a.m. and 8 p.m. The study used morning urine tested in a lab, but at home, afternoon testing is still recommended. LH usually takes a few hours to build up in your urine to a level a home ovulation test can pick up. Testing twice a day helps if your surge tends to be quick.
- Watch your LH as a number, not just a line. Your home readings won’t match the study’s lab numbers, but seeing the rise as a trend makes it easier to notice when your surge starts.
- Use first morning urine for PdG. It’s the most concentrated sample of the day, and it’s what the study used too.
- Read PdG strips differently from ovulation tests. On many PdG test strips, no test line means positive and a visible test line means negative. Yes, it’s backwards.
- Follow your PdG test’s instructions on when to start and how often to test. This study is helpful background, but it doesn’t replace them.
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Here’s how the ways most people track LH compare with what the researchers used.
| Method | What it shows you | How it relates to this study |
|---|---|---|
| Ultrasound at a clinic | When a follicle releases its egg | What the researchers used as the reference. Not practical for most people month to month. |
| Line-only ovulation tests | Whether LH is above the test’s threshold that day | The authors say their method can’t be assumed to work the same way with these tests. |
| Ovulation tests read as numbers in an app | An estimated LH number each day, drawn as a curve next to PdG and BBT | Gives you a daily LH number like the study did, though home readings are on a different scale than the lab test. |
| Basal body temperature (BBT) | A temperature rise that usually shows up 1 to 3 days after ovulation | Not part of this study, but a helpful second sign that ovulation likely happened. |
What doesn’t this study tell you about PdG testing?
The authors are careful about what their study can and can’t say. They describe their method as “a candidate timing strategy rather than a clinically actionable decision rule.” In plain terms, it’s a promising starting point, not a rule a doctor would use on its own. A few other limits to keep in mind:
- The women were healthy and ovulating regularly. The results may not apply if you have PCOS, irregular cycles, diminished ovarian reserve, or infertility, or if you use hormonal birth control or fertility medications.
- The samples are from 1996 and 1997 and were tested in a lab. Today’s home tests work differently, so the specific numbers would need to be checked on each device.
- It didn’t look at pregnancy, implantation, or miscarriage. Nothing here links a PdG number to your chances of getting pregnant.
- It looked back at old data instead of following women forward. The authors call the results hypothesis-generating, which means they point to what future studies should test.
- The LH and PdG levels in it (15 mIU/mL and 15 µg/mL) are research reference points from a lab test, not cutoffs for any home test.
And if you’re staring at a negative PdG test at 8 DPO, one low reading doesn’t mean your progesterone is low. The study didn’t look at what to do after a low result, either.
It’s worth talking to your doctor if your PdG tests stay negative through your luteal phase, your luteal phase is 10 days or shorter, or you don’t see an LH rise or a BBT shift at all.
Why time PdG from your own LH instead of a calendar date?
Ovulation doesn’t happen on the same day for all women, or even on the same day for you from one cycle to the next. That’s why a fixed date, like testing on cycle day 21, can miss the mark.
The most useful idea in this study is simple: time your PdG test from what your own LH is doing that cycle. Track your LH as a number, give PdG time to catch up, and see any single result as one piece of the picture.
How can Premom help you track LH and PdG together?
Premom is a free ovulation and cycle tracking app that reads easy@Home ovulation and PdG test strips. Snap a photo of your strip and the app reads the result for you, so you’re not squinting at lines and second-guessing yourself.
Each LH test becomes a number, and those numbers form a curve, so it’s easier to see when your surge starts and where it peaks. In the days after, your PdG results show up on the same chart, next to other fertile signs like BBT if you track it.
Premom also uses your test results and cycle history to predict your fertile window, so you can see your best days to try coming up instead of guessing from a calendar. It’s free to download, and your chart starts building from your first test.
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Key terms explained
Luteinizing hormone (LH): The hormone that triggers ovulation. Ovulation tests measure it in urine.
LH surge: The rise in LH before ovulation. This study counted from the first day LH reached a set level on a lab test.
LH peak: Your highest LH reading of the cycle, usually the darkest test line. It’s easiest to spot looking back.
Pregnanediol glucuronide (PdG): What progesterone becomes after your body breaks it down and passes it in urine. It rises after ovulation.
Luteal phase: The days from ovulation to the day before your next period, usually 11 to 17 days.
Ultrasound ovulation day: The day a scan shows a follicle has released its egg. Researchers use it as the reference point for timing.
