Pregnanediol Glucuronide (PDG) is a key reproductive hormone metabolite that offers a window into the body’s progesterone activity. Progesterone is often referred to as the “pregnancy hormone” because of its role in preparing and sustaining the uterine environment. PDG is the substance created when the body processes and breaks down progesterone, making it a reliable, non-invasive marker for progesterone levels. Tracking PDG is relevant for assessing a person’s fertility and monitoring the health of a pregnancy, particularly in the early stages.
The Connection Between Progesterone and PDG
Progesterone is an active steroid hormone produced primarily by the corpus luteum, the temporary gland that forms in the ovary after ovulation. This hormone circulates through the bloodstream, transforming the uterine lining (endometrium) to make it receptive for a fertilized egg. Progesterone supports the uterine lining, prevents contractions, and prepares the environment for potential implantation and growth of an embryo.
Once progesterone has performed its biological functions, the body breaks it down for removal through metabolism, mainly in the liver. The active progesterone molecule is chemically converted into various inactive substances. The primary breakdown product is pregnanediol, which is then joined with glucuronic acid to form Pregnanediol Glucuronide (PDG).
PDG is significantly less active than progesterone and is water-soluble, allowing the body to excrete it through the kidneys and into the urine. Because PDG is a stable, measurable waste product, its concentration in the urine reflects the average amount of progesterone that was circulating in the bloodstream. Measuring PDG in urine provides a convenient, non-invasive way to indirectly confirm that the active hormone was present and functioning.
Monitoring PDG for Ovulation Confirmation
The primary application of PDG testing is to confirm that ovulation has successfully occurred. After the egg is released, the remaining follicle transforms into the corpus luteum, which produces progesterone. This surge in progesterone stabilizes the uterine lining for potential implantation.
PDG levels begin to rise in the urine 24 to 72 hours after the luteinizing hormone (LH) surge, which predicts the impending release of the egg. While LH tests predict the fertile window, PDG tests confirm the event, acting as retrospective proof of ovulation. Sustained elevation of PDG, rather than a single measurement, indicates a functional corpus luteum.
PDG levels are monitored in the luteal phase, the second half of the menstrual cycle following ovulation. A PDG level sustained above a certain threshold, often 5 µg/mL for three consecutive days, indicates that ovulation has occurred. This sustained elevation is important for assessing “luteal phase adequacy,” which refers to whether the progesterone produced is sufficient to prepare the uterine lining.
Progesterone levels peak approximately six to eight days after ovulation, the optimal time for an embryo to implant. If PDG levels fail to rise or drop prematurely during this window, it may suggest a luteal phase defect, meaning the uterine environment may not be receptive. Testing PDG over multiple days provides a clearer picture of overall progesterone production than a single blood draw, which can miss the hormone’s natural fluctuations.
PDG Levels During Early Pregnancy
Once pregnancy is established, PDG remains a significant marker, reflecting the continued production of progesterone necessary to sustain the gestation. Progesterone maintains the uterine environment and ensures the lining remains thick and vascularized to support the developing embryo. If implantation occurs, the embryo produces human chorionic gonadotropin (hCG), which signals the corpus luteum to continue high-level progesterone production.
This continued progesterone production keeps PDG levels elevated well beyond a non-pregnant cycle. In early pregnancy, high PDG levels are associated with a viable and progressing gestation. Conversely, sustained low or dropping PDG levels, reflecting low progesterone, can be a warning sign.
Low progesterone levels are often a symptom of an unhealthy or non-viable pregnancy, such as threatened miscarriage or ectopic pregnancy. The embryo’s inability to produce adequate hCG means the corpus luteum does not receive the signal to maintain progesterone, leading to a drop in PDG. While blood progesterone levels between 10–30 ng/mL are considered encouraging in the first few weeks, a level below 10 ng/mL may signal an insufficient hormonal environment.
Around the 8th to 12th week of gestation, hormone production shifts from the corpus luteum to the newly developed placenta in the luteal-placental shift. The placenta then takes over, secreting the large amounts of progesterone needed for the remainder of the pregnancy. PDG levels continue to rise throughout the second and third trimesters, providing an accessible way to track this overall hormonal trend.