PdG stands for pregnanediol glucuronide, a substance your body produces when it breaks down progesterone. It shows up in urine, which makes it useful for at-home fertility tracking. While progesterone itself requires a blood draw to measure, PdG gives you a way to confirm ovulation happened without visiting a lab.
How Your Body Makes PdG
After ovulation, your ovaries produce progesterone to prepare the uterine lining for a potential pregnancy. Your liver then processes that progesterone and converts it into pregnanediol, which gets further modified into pregnanediol glucuronide. This is the form your kidneys can filter out and excrete in urine. The amount of PdG in your urine reflects how much progesterone your body produced, though the exact ratio varies with age, stage of the menstrual cycle, and individual metabolism.
Why PdG Matters for Confirming Ovulation
Ovulation predictor kits that measure LH (luteinizing hormone) tell you ovulation is likely about to happen. PdG does something different: it tells you ovulation already occurred. Progesterone only rises significantly after the egg is released, so detecting its metabolite in urine serves as confirmation that you’ve entered the luteal phase, the second half of your cycle.
PdG becomes detectable in urine about 24 to 36 hours after ovulation and typically reaches levels high enough to register on a test strip (5 micrograms per milliliter or above) around five days after a positive ovulation test. Levels peak roughly seven days after the LH surge. This is why the traditional “day 21” blood progesterone test exists. It targets the same window, just through a different measurement method. A blood progesterone level above 5 ng/mL confirms ovulation took place, and levels above 10 ng/mL suggest a strong luteal phase.
When and How to Test
Most at-home PdG test strips are designed to be used with your first morning urine, since overnight concentration gives the most reliable reading. The general approach is to start testing five days after you get a positive result on an LH-based ovulation test. If the result is negative, you continue testing daily until you either get a positive or your next period arrives.
A single positive PdG test confirms that progesterone rose after ovulation. Some fertility apps and tracking methods look for multiple positive results across several consecutive days, since sustained progesterone matters more for implantation than a single spike. Seeing positive PdG readings on consecutive days during the luteal phase suggests your body is maintaining the hormonal environment needed to support early pregnancy.
What Low PdG Levels Can Indicate
If PdG tests remain negative after you expected ovulation, a few things could be going on. You may not have ovulated despite an LH surge (LH can rise without triggering egg release). Or your progesterone levels may be too low to produce enough PdG to register on a test strip.
Persistently low progesterone after ovulation is sometimes called luteal phase deficiency, characterized by a luteal phase lasting 10 days or fewer. It has been linked to short menstrual cycles, spotting before your period starts, difficulty conceiving, and early pregnancy loss. Research from the American Society for Reproductive Medicine notes that reduced PdG excretion has been observed in women with obesity compared to normal-weight controls, suggesting body composition can influence progesterone metabolism. That said, the same research found that luteal phase deficiency can show up in random cycles of otherwise normally menstruating women, and the evidence that it independently causes infertility or pregnancy loss remains limited.
PdG Testing vs. Blood Progesterone
The main advantage of PdG testing is convenience. You can do it at home, daily, without scheduling a blood draw. This gives you a fuller picture across multiple days rather than a single snapshot. A day 21 blood test might catch your progesterone on a high or low point of its natural fluctuation, since progesterone is released in pulses throughout the day.
The trade-off is precision. Blood tests give an exact progesterone number in ng/mL, which a doctor can use to evaluate luteal phase quality more precisely. PdG strips give a positive or negative result based on a threshold, not a specific value. For someone trying to get a general sense of whether ovulation is happening cycle after cycle, PdG strips work well. For someone being evaluated for fertility treatment, blood progesterone provides more actionable clinical detail.
Who Benefits Most From PdG Tracking
PdG testing is most useful if you’re actively trying to conceive and want confirmation that ovulation is actually completing, not just that an LH surge occurred. It’s also helpful if you have irregular cycles and want to identify patterns over several months. Combining LH testing (to predict ovulation) with PdG testing (to confirm it) gives you both sides of the ovulation picture without any lab visits.
If your PdG tests are consistently negative in the days following a positive ovulation test, that pattern is worth bringing to a reproductive endocrinologist. It doesn’t necessarily mean something is wrong, but it gives your doctor a useful data point when deciding whether further evaluation is needed.