Progesterone is a naturally occurring hormone, often called the “pregnancy hormone,” that plays a central role in the reproductive cycle. Its primary function is to prepare the lining of the uterus, the endometrium, for the potential implantation of a fertilized egg by making it thicker and more stable. When supplemental progesterone is stopped, the subsequent decline in hormone levels triggers withdrawal bleeding. This process mimics the natural hormonal drop at the end of a non-pregnant cycle, prompting the uterine lining to shed.
The Expected Timeline for Withdrawal Bleeding
The onset of bleeding after the last dose of supplemental progesterone is typically predictable, though it does not begin immediately. Most individuals who have been adequately primed with estrogen and progesterone will experience withdrawal bleeding within a window of two to seven days after stopping the medication. This slight delay is due to the time required for the circulating levels of the administered hormone to drop significantly.
The drop in progesterone triggers a cascade of biochemical changes in the uterine lining, causing tissue breakdown. While some women may start spotting as early as 48 hours after their final dose, a range of three to five days is the most commonly reported timeframe for the start of the flow. The specific progesterone formulation and dosage used can also influence the exact timing of the withdrawal bleed.
This flow is medically referred to as a withdrawal bleed because it is induced by the cessation of external hormones. The response is considered successful if bleeding, even light bleeding, occurs within the expected seven-day window.
Common Reasons for Progesterone Prescription
Supplemental progesterone is prescribed primarily to regulate the reproductive cycle or support a potential pregnancy. One major application is inducing a period in women experiencing amenorrhea (absence of menstruation), often due to conditions like Polycystic Ovary Syndrome (PCOS) or functional hypothalamic amenorrhea.
A short course of progesterone stabilizes and matures the uterine lining, ensuring it is properly shed when the medication is stopped. This shedding helps establish a more regular cycle or confirms that the amenorrhea is due to hormonal imbalance.
Progesterone is also used for luteal phase support, especially during assisted reproductive technologies like in vitro fertilization (IVF) or to prevent threatened miscarriage. Following ovulation or an embryo transfer, progesterone maintains the thick, supportive endometrial lining necessary for implantation and early pregnancy development. The medication is continued until pregnancy is confirmed. If the pregnancy test is negative, it is stopped, leading to withdrawal bleeding.
When Bleeding is Delayed or Fails to Occur
Failure to bleed within the standard two-to-seven-day window warrants further investigation. The most important reason for a delayed or absent withdrawal bleed is pregnancy. If an embryo successfully implants, the developing placenta begins producing Human Chorionic Gonadotropin (hCG), which signals the body to continue producing high levels of progesterone. This ongoing hormonal support overrides the effects of stopping the supplemental medication, preventing the uterine lining from shedding. Therefore, if bleeding does not occur, a pregnancy test is the first necessary troubleshooting step.
Another cause for a failed bleed is insufficient estrogen exposure before the progesterone was administered. If the body’s natural estrogen levels were too low, the endometrium may not have built up a sufficient thickness to shed when the progesterone was withdrawn. In this case, there is simply not enough tissue present to result in a noticeable flow.
Less commonly, failure to bleed can point to an issue with the uterine cavity itself, such as severe scarring or adhesions that physically obstruct the outflow of blood. If no bleeding occurs within ten to fourteen days of stopping the medication, contacting a healthcare provider is recommended to determine the cause and plan any necessary next steps.