Bleeding Between Periods: What Causes Spotting or Intermenstrual Bleeding

What is the difference between spotting and intermenstrual bleeding?

Not all mid-cycle bleeding is the same. Light spotting — a small amount of pink or brown blood lasting a day or two — is generally low-concern, especially when it coincides with ovulation around the middle of the cycle. Heavier mid-cycle bleeding, bright-red blood that soaks a liner or pad, or bleeding that recurs across multiple cycles is more clinically significant.

Postcoital bleeding (bleeding after sex) is also considered abnormal and warrants evaluation, since it can signal cervical conditions 1Ref 1US Preventive Services Task Force (2018).Screening for Cervical Cancer: US Preventive Services Task Force Recommendation Statement.Cervical cancer screening (Pap smear/HPV co-test) is recommended on established schedules; postcoital or unexplained irregular bleeding can be a sign of cervical pathology warranting screening evaluation. Bleeding that is genuinely between periods — not just a longer or heavier period — is what clinicians classify as intermenstrual bleeding.

What commonly causes bleeding between periods?

Ovulation spotting is natural and occurs when the follicle releasing the egg causes a brief hormonal dip. It typically appears mid-cycle as light pink or brown spotting lasting one to two days.

Hormonal contraception — including the pill, patch, ring, hormonal IUD, or implant — is one of the most common causes of breakthrough bleeding, particularly in the first few months of use or after missed doses 2Ref 2American College of Obstetricians and Gynecologists (2019).ACOG Practice Bulletin No. 206: Use of Hormonal Contraception in Women With Coexisting Medical Conditions.Breakthrough bleeding is a recognized side effect of hormonal contraception including the pill, patch, ring, IUD, and implant. This is a recognized and expected side effect, not a sign of contraceptive failure.

Implantation bleeding can occur about 6–12 days after conception when a fertilized egg attaches to the uterine lining. It is typically very light and brief.

Cervical or vaginal infections, including STIs such as chlamydia or gonorrhea, can cause inflammation that leads to spotting or bleeding after sex 3Ref 3US Preventive Services Task Force; Davidson KW, Barry MJ, Mangione CM, et al. (2021).Screening for Chlamydia and Gonorrhea: US Preventive Services Task Force Recommendation Statement.Chlamydia and gonorrhea are STIs that can cause abnormal vaginal bleeding; screening is recommended for sexually active people under 25 and older people with risk factors. Annual screening is recommended for sexually active people under 25 and for older people with risk factors 3Ref 3US Preventive Services Task Force; Davidson KW, Barry MJ, Mangione CM, et al. (2021).Screening for Chlamydia and Gonorrhea: US Preventive Services Task Force Recommendation Statement.Chlamydia and gonorrhea are STIs that can cause abnormal vaginal bleeding; screening is recommended for sexually active people under 25 and older people with risk factors.

Cervical polyps — small, usually benign growths on the cervix — are a common structural cause of irregular spotting, especially postcoital bleeding.

Thyroid dysfunction can disrupt cycle regularity, sometimes causing irregular or intermenstrual bleeding 4Ref 4Jonklaas J, Bianco AC, Bauer AJ, et al. (2014).Guidelines for the Treatment of Hypothyroidism: Prepared by the American Thyroid Association Task Force on Thyroid Hormone Replacement.Thyroid dysfunction can disrupt menstrual cycle regularity, including causing intermenstrual bleeding; TSH testing is an appropriate workup step.

Which causes require prompt evaluation?

Some causes of intermenstrual bleeding need more urgent attention.

Uterine fibroids and uterine polyps can both cause irregular bleeding and are detected by pelvic ultrasound. Fibroids are noncancerous growths in the uterine wall; polyps are small growths of the uterine lining.

Cervical or uterine pathology — including precancerous cell changes or cervical cancer — can present as postcoital or irregular bleeding 1Ref 1US Preventive Services Task Force (2018).Screening for Cervical Cancer: US Preventive Services Task Force Recommendation Statement.Cervical cancer screening (Pap smear/HPV co-test) is recommended on established schedules; postcoital or unexplained irregular bleeding can be a sign of cervical pathology warranting screening evaluation. Cervical cancer screening with Pap smear and HPV testing is recommended on established schedules for this reason 1Ref 1US Preventive Services Task Force (2018).Screening for Cervical Cancer: US Preventive Services Task Force Recommendation Statement.Cervical cancer screening (Pap smear/HPV co-test) is recommended on established schedules; postcoital or unexplained irregular bleeding can be a sign of cervical pathology warranting screening evaluation.

Early pregnancy complications — miscarriage or ectopic pregnancy — must be ruled out in anyone of reproductive age who could be pregnant. Ectopic pregnancy, in particular, can be life-threatening.

STIs are an important and treatable cause worth ruling out whenever risk factors are present 3Ref 3US Preventive Services Task Force; Davidson KW, Barry MJ, Mangione CM, et al. (2021).Screening for Chlamydia and Gonorrhea: US Preventive Services Task Force Recommendation Statement.Chlamydia and gonorrhea are STIs that can cause abnormal vaginal bleeding; screening is recommended for sexually active people under 25 and older people with risk factors.

When should you see a clinician?

See a clinician for bleeding between periods that: recurs over two or more cycles; is accompanied by pelvic pain, fever, or discharge; happens after sex; occurs after menopause; or is heavy enough to concern you. A single episode of light spotting around ovulation in an otherwise healthy person with no other symptoms can reasonably be observed through one more cycle before seeking care. When something feels wrong, a prompt visit is always the right call.

Tests a clinician may order include a pelvic exam, pregnancy test, STI screening 3Ref 3US Preventive Services Task Force; Davidson KW, Barry MJ, Mangione CM, et al. (2021).Screening for Chlamydia and Gonorrhea: US Preventive Services Task Force Recommendation Statement.Chlamydia and gonorrhea are STIs that can cause abnormal vaginal bleeding; screening is recommended for sexually active people under 25 and older people with risk factors, Pap smear, pelvic ultrasound, TSH (if thyroid dysfunction is suspected 4Ref 4Jonklaas J, Bianco AC, Bauer AJ, et al. (2014).Guidelines for the Treatment of Hypothyroidism: Prepared by the American Thyroid Association Task Force on Thyroid Hormone Replacement.Thyroid dysfunction can disrupt menstrual cycle regularity, including causing intermenstrual bleeding; TSH testing is an appropriate workup step), and, in some cases, endometrial biopsy.