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An early pregnancy with spotting
Implantation bleeding is usually earlier than day 35 if ovulation was around day 14, but ovulation can be later than expected. A positive test with spotting needs clinical advice.
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Very early miscarriage / biochemical pregnancy
This can present as a late, lighter or unusual period, with red or brown mucus and then bleeding.
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Delayed menstruation from delayed ovulation or an anovulatory cycle
Stress, illness, weight change, travel, thyroid issues, PCOS, or normal cycle variation may delay bleeding. Anovulatory cycles often cause unpredictable timing and bleeding. Textbook of Family Medicine, p. 616.
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Cervical or vaginal cause
Recent intercourse, cervical ectropion/polyp, or cervicitis can cause blood-stained mucus. Infection is more likely if there is odor, itching, burning, pain during sex/urination, pelvic pain, or yellow-green/pus-like discharge. Intermenstrual bleeding can arise from cervical infection or other cervical pathology. Textbook of Family Medicine, p. 616.
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Ectopic pregnancy, which must not be missed
It is less common, but any possible pregnancy plus abnormal bleeding needs this considered, particularly with one-sided lower abdominal pain, shoulder-tip pain, dizziness, or fainting. The
NHS ectopic-pregnancy guidance advises urgent assessment for these symptoms.