The Endometrial Receptivity Analysis (ERA) test is a diagnostic procedure used in fertility treatments to identify the precise moment a person’s uterine lining is most prepared to receive an embryo. It is often recommended after failed frozen embryo transfers to personalize the timing of a future transfer. The ERA involves a “mock cycle” that mirrors hormonal preparation for a standard transfer, culminating in a small biopsy of the uterine lining. The results guide specialists in determining the optimal window of implantation unique to the patient.
The Hormonal Setup of the ERA Test
The ERA test requires a controlled hormonal environment established through a mock cycle protocol. This process begins with administering estrogen, which thickens the endometrial lining and prepares the tissue for progesterone. Once the lining is thick enough, the patient starts progesterone, which makes the endometrium receptive. The biopsy is performed after a specific number of days of progesterone exposure to analyze the endometrial cells.
Menstruation, or withdrawal bleeding, is a direct result of stopping these prescribed hormones, specifically progesterone. High levels of progesterone artificially maintain the thickened uterine lining. When the medication is discontinued, the sudden drop in hormone levels signals the body to shed that lining. This physiological process mimics the end of a natural menstrual cycle.
Typical Timeline for Menstruation
Menstruation begins within three to seven days after the final dose of progesterone is taken. This timing is predictable because the period results from the intentional withdrawal of administered medication, not the body’s natural cycle hormones. Most clinics advise patients to expect bleeding around the fourth or fifth day following cessation of progesterone.
The resulting menstrual flow is often heavier and potentially more painful than a typical period. The mock cycle builds a thick, robust uterine lining to optimize the biopsy environment. When this significantly thickened tissue is shed, the volume of blood loss and the intensity of cramping are often increased compared to a regular spontaneous cycle.
This withdrawal bleed marks the completion of the ERA cycle and serves as “Day 1” for the next cycle. This allows the patient to progress quickly with their fertility plan, often a personalized frozen embryo transfer.
Why Timing Varies
While the three-to-seven-day window is the general expectation, the exact timing of the withdrawal bleed varies based on individual and treatment factors. The specific dosage and route of progesterone administration is a significant variable. Progesterone methods—vaginal insert, oral tablet, or injection—clear from the body at different rates.
An individual’s unique metabolic rate also influences how quickly the liver processes and eliminates synthetic hormones. Faster metabolism leads to an earlier drop in hormone levels and sooner bleeding, while slower metabolism can delay the period.
Underlying endocrine conditions or differences in body mass index (BMI) can also affect hormone processing and clearance. Furthermore, chronic endometritis, a persistent inflammation of the uterine lining, may affect how the endometrium responds to hormonal manipulation.
What to Do If Your Period is Delayed
If menstruation does not arrive within a week of stopping progesterone, specific steps should be taken. The first action is to perform a home pregnancy test, as a delayed period always requires ruling out unexpected conception, even after a diagnostic mock cycle.
If the period is significantly delayed, such as beyond 10 days after the last dose, contact the fertility clinic. The medical team may recommend a blood test to confirm hormone levels have dropped sufficiently to trigger the bleed. Occasionally, a brief course of different medication is needed to initiate the shedding of the uterine lining.
Any delay exceeding two weeks, or the presence of concerning symptoms like unusual pain or fever, warrants a prompt consultation with a specialist. Open communication ensures the next cycle of treatment can be planned accurately.