When a period starts, pauses, and then resumes, or when bleeding occurs outside the expected menstrual window, it is known as irregular uterine bleeding or spotting. This unpredictable pattern is a common symptom with a wide range of underlying causes, from hormonal adjustments to structural issues. Understanding the mechanisms behind this starting and stopping pattern is the first step toward determining if medical evaluation is necessary. Causes are generally grouped into systemic hormonal fluctuations, local physical changes, or pregnancy-related events.
Hormonal Shifts and Cycle Adjustments
The most frequent cause of irregular bleeding involves a temporary imbalance in the hormones that regulate the monthly cycle: estrogen and progesterone. These hormones orchestrate the thickening and shedding of the uterine lining, and any disruption to their balance can destabilize the process, leading to the unpredictable flow known as breakthrough bleeding. Hormonal contraceptives are a common source of this instability, particularly in the first three months after starting a new pill, patch, ring, or injection. The synthetic hormones in these methods work to thin the uterine lining, and the body takes time to adjust to these altered levels, which often results in intermittent spotting.
Missing a dose of hormonal birth control, or taking it inconsistently, can also cause a sudden dip in hormone levels, triggering a temporary shedding of the uterine lining and subsequent bleeding. Beyond medication, natural life stages feature dramatic hormonal shifts that cause this irregularity. The years immediately following puberty and the transitional phase leading up to menopause, known as perimenopause, are times when the ovaries produce estrogen and progesterone erratically, resulting in unpredictable bleeding patterns.
External factors that impact the body’s overall hormonal environment also play a role. Chronic stress elevates cortisol levels, which can interfere with the hypothalamic-pituitary-gonadal (HPG) axis, the central regulator of reproductive hormones. Changes in body weight, whether gain or loss, or engaging in extreme exercise, can disrupt the balance of reproductive hormones. These physiological stressors can temporarily suppress ovulation or alter estrogen metabolism, manifesting as spotting or a period that erratically starts and stops.
Physical Changes in the Reproductive Tract
The physical structure of the cervix and uterus can be a direct source of intermittent bleeding, independent of hormonal imbalances. Uterine polyps are noncancerous overgrowths of cells on the inner lining of the uterus that commonly cause irregular bleeding between expected periods. These growths are highly vascularized and can bleed easily when irritated or when the surrounding uterine lining sheds. Uterine fibroids, which are benign muscular tumors within the walls of the uterus, can disrupt the normal bleeding pattern. If they bulge into the uterine cavity, fibroids can interfere with the stability of the endometrial lining, leading to prolonged or erratic flow.
Infections can cause inflammation and fragility of the reproductive tract tissues, resulting in spotting. Sexually transmitted infections (STIs) such as chlamydia or gonorrhea, or pelvic inflammatory disease (PID), can cause the cervix and uterine lining to become inflamed. The resulting irritation can lead to bleeding that occurs between periods or after sexual intercourse. In these cases, the bleeding is often accompanied by other symptoms, such as unusual discharge or pain.
Bleeding Related to Early Pregnancy
For many individuals, any unexpected bleeding is a concern regarding pregnancy, and several conception-related events can cause a starting and stopping pattern. Implantation bleeding occurs when a fertilized egg attaches to the uterine wall, resulting in light spotting around the time a period would have been expected. This brief, light flow is often mistaken for a very short or unusual period. However, concerns like a threatened or early miscarriage also commonly present with intermittent bleeding.
In cases of miscarriage, the bleeding may begin as light spotting, stop, and then resume, sometimes becoming heavy with clots as the body attempts to expel the pregnancy tissue. An ectopic pregnancy, where the fertilized egg implants outside the uterus (usually in a fallopian tube), is another cause of irregular flow. Bleeding from an ectopic pregnancy is often described as light, watery, or dark brown discharge that starts and stops, frequently accompanied by abdominal pain localized to one side. Because an ectopic pregnancy is a medical emergency if the tube ruptures, any irregular bleeding combined with a positive pregnancy test requires immediate medical evaluation.
When Irregular Bleeding Requires a Doctor’s Visit
While many causes of a starting and stopping period are benign, certain symptoms require medical attention to rule out serious conditions. It is advisable to consult a healthcare provider if the irregular bleeding persists for more than a few cycles, becomes heavier than a normal period, or if you experience any bleeding after menopause. Other urgent warning signs include severe pelvic pain, dizziness, or a fever, which could indicate a serious infection or a ruptured ectopic pregnancy.
When preparing for a medical visit, keeping a detailed record of the bleeding is helpful for diagnosis. This record should include:
- Timing
- Duration
- Flow intensity
- Any associated pain
The diagnostic process will begin with a physical exam, possibly including a pelvic ultrasound to visualize the uterus and ovaries for structural issues like polyps or fibroids. Blood tests may also be ordered to check for hormonal imbalances, anemia from blood loss, or a pregnancy. This approach allows a provider to accurately identify the underlying cause and recommend the appropriate course of treatment.