Pregnanediol Glucuronide (PDG) is the main breakdown product, or metabolite, of the hormone progesterone. PDG is measured in urine, offering a non-invasive way to gain insight into the menstrual cycle. A positive PDG test provides specific information about an event that has already occurred in the body. This confirmation is useful for those trying to understand their reproductive cycles and optimize timing for conception.
The Role of Progesterone and PDG
Progesterone is central to the second half of the menstrual cycle, known as the luteal phase. After ovulation, the ovarian follicle transforms into the corpus luteum, which produces large amounts of progesterone. The function of this progesterone surge is to prepare the uterine lining (endometrium) for potential implantation. Progesterone causes the lining to thicken and become receptive, creating a supportive environment for a fertilized egg.
The body metabolizes circulating progesterone, and the residue is excreted in the urine as PDG. Measuring PDG levels serves as an indirect but reliable way to monitor progesterone production. Studies show that PDG measured in first morning urine closely correlates to the average blood progesterone levels from the previous day. This makes at-home PDG testing a practical tool for assessing the quality of the luteal phase.
What a Positive PDG Test Confirms
A positive PDG test confirms that ovulation has successfully occurred. The rise in PDG only happens when the corpus luteum has formed and is producing progesterone in response to the egg’s release. Most at-home tests are calibrated to turn positive when the PDG concentration in urine exceeds a threshold of around 5 µg/mL, a level accepted as confirming an ovulatory event.
This post-ovulation confirmation contrasts with Luteinizing Hormone (LH) tests, which only detect the surge that predicts ovulation is about to happen. PDG provides retrospective proof, verifying that the predicted event took place and that the resulting progesterone production is substantial. To capture the peak of progesterone activity, testing is recommended to begin 7 to 10 days after the peak fertility period. Receiving a positive result in this window validates the successful transition into the luteal phase.
Interpreting Results for Conception Success
While a positive PDG test confirms an egg was released, it is only one component of successful conception. For an embryo to implant successfully, progesterone levels must be sustained at a high level over multiple days to maintain the receptive uterine environment. Tracking PDG over several days during the implantation window (approximately 7 to 10 days after ovulation) provides a more complete picture of the cycle’s quality. A single positive result is not a guarantee of a healthy luteal phase, but multiple positive results indicate the body is maintaining the necessary hormonal support.
The duration of elevated progesterone is highly significant, as the luteal phase needs to be long enough to allow for implantation of the fertilized egg. A phase lasting less than 10 days, even with a positive PDG result, may suggest a short luteal phase. Consistently insufficient PDG levels can point toward a Luteal Phase Defect (LPD), where the uterine lining is not adequately prepared for pregnancy. Therefore, the pattern of sustained elevation, not just a single positive result, truly supports the best chance of conception.
When to Seek Medical Guidance
Interpreting PDG tests should guide further action, especially if conception is not occurring after several cycles. A consistently negative PDG test, or one showing insufficient levels, is a direct signal to consult a healthcare provider, as it may indicate an underlying issue with ovulation or progesterone production. Even individuals with recurrent positive PDG tests who are not achieving pregnancy after several months should seek professional advice. The data gathered from tracking PDG provides valuable information to share with a doctor.
A medical professional may order a quantitative serum progesterone test, which measures the precise concentration of progesterone in the blood, offering a more exact reading than threshold-based urine tests. They will also investigate if the luteal phase length is consistently short (defined as 10 days or less). These steps help determine if hormonal supplementation or other interventions may be necessary to support the uterine environment for a successful pregnancy.