Differential Diagnosis
Given the symptoms and scenario, here's a structured approach to the differential diagnosis:
Single Most Likely Diagnosis
- Early Pregnancy: The patient is 16 days past ovulation, which aligns with the timing of early pregnancy. The recent cessation of vaginal progesterone and the absence of menstruation further support this possibility, as progesterone is crucial for maintaining early pregnancy and its withdrawal can lead to menstruation unless pregnancy has occurred.
Other Likely Diagnoses
- Progesterone Withdrawal: Stopping vaginal progesterone 2 days ago could lead to withdrawal bleeding, which might be imminent but hasn't started yet. This is a common phenomenon when exogenous progesterone is discontinued.
- Luteal Phase Defect: This condition occurs when the corpus luteum does not produce enough progesterone, or the uterus lining does not respond to progesterone, potentially leading to irregular menstrual cycles or early miscarriage. The recent cessation of progesterone supplementation might unmask this issue.
- Stress or Other Factors Affecting Menstrual Cycle: Stress, weight changes, or other environmental factors can affect the menstrual cycle, potentially delaying ovulation or menstruation.
Do Not Miss Diagnoses
- Ectopic Pregnancy: Although less likely, an ectopic pregnancy must be considered, especially if the patient experiences any abdominal pain or significant bleeding. Ectopic pregnancies can be life-threatening if not promptly diagnosed and treated.
- Ovarian Torsion or Other Gynecologic Emergencies: These conditions, though rare, are emergencies that could present with abdominal pain and potentially altered menstrual patterns. They require immediate medical attention.
Rare Diagnoses
- Pituitary or Adrenal Disorders: Certain disorders affecting the pituitary or adrenal glands can influence menstrual cycles and progesterone levels, though these are less common and would typically be associated with other systemic symptoms.
- Thyroid Dysfunction: Both hyperthyroidism and hypothyroidism can affect menstrual regularity, though this would be less directly related to the cessation of progesterone supplementation and the specific timing post-ovulation.