Causes of abnormal bleeding between periods

The colour or amount of blood cannot identify the cause on its own. A clinician may need to consider pregnancy, medicines, sexual health, the cervix and the lining of the womb.

Spotting can occur when hormone levels fluctuate, after starting or changing hormonal contraception, or when a dose is missed. Bleeding can also arise from irritation or inflammation of the vagina or cervix, including a sexually transmitted infection such as chlamydia.

Structural causes include endometrial polyps and uterine fibroids. Cervical dysplasia, cervical cancer and womb cancer can present with unexpected vaginal bleeding, but bleeding between periods is not enough to determine that any of these is present.

Arrange a medical assessment for bleeding that is new, unexplained, repeated or different from your normal cycle. Take a pregnancy test if pregnancy is possible, and seek sexual-health testing if there is a possibility of infection.

Record when the bleeding started, whether it followed sex, its flow and colour, and any pain, discharge, fever, dizziness or missed period. Bring a list of contraception, supplements and medicines, especially medicines that affect blood clotting.

Seek urgent medical care if bleeding is heavy, you feel faint or very weak, or you have severe or worsening pelvic pain. Bleeding with a missed period and abdominal or pelvic pain needs prompt assessment because an ectopic pregnancy must be ruled out.

Fever, foul-smelling discharge or marked pelvic tenderness also warrants prompt attention because infection may need treatment. Any vaginal bleeding after menopause should be assessed without delay, even when it happens only once.

Ask whether you need a pregnancy test, blood test, infection swab, cervical examination or pelvic ultrasound. It can also help to ask whether contraception or another medicine could be contributing and what change in bleeding should trigger urgent care.