Why a period is not possible during pregnancy
Menstruation is the shedding of the built-up uterine lining without pregnancy. If pregnancy has occurred, the lining remains to support the embryo. Bleeding during pregnancy therefore has other causes — never a regular menstrual period.
Period vs. pregnancy bleeding – how to tell
Period: heavier, steady flow over 3–7 days, recurring in cycles, often with cramp-like menstrual pain.
Pregnancy bleeding: usually spotty or streaky, light to dark red, lasting hours up to a few days, not cyclical.
Quick check: colour, amount & accompanying signs
- Pale pink or brown, very little: often implantation bleeding or hormonal withdrawal around the expected period date.
- Bright red after sex/examination: typical contact bleeding from the sensitive cervix; usually settles quickly.
- Dark red, heavier, with tissue: a warning sign of possible miscarriage — seek medical assessment.
- Massive bleeding + one-sided pain/dizziness: suspicion of ectopic pregnancy or placental complication — go to the emergency department immediately.
Common causes of bleeding in pregnancy
Implantation bleeding
6–12 days after fertilisation: small vessels break when the blastocyst implants. Very light, pale pink/brown, usually up to 1–2 days. More information: ACOG.
Pseudo-menstruation (hormonal withdrawal bleed)
Short-term hormonal fluctuations can cause a small bleed around the expected period date. Clearly less and shorter than a normal period.
Contact bleeding
During pregnancy the cervix is highly vascular. A vaginal exam or intercourse can irritate small vessels. Bright red, usually stops within a few hours.
Cervical causes, infections & minor injuries
Cervical polyp, ectropion, bacterial vaginosis or yeast infection can cause spotting. Swab and targeted treatment. Info: NHS.
Subchorionic haematoma
Collection of blood between the chorion and uterine wall. Common finding in early pregnancy ultrasound. Management depends on size with follow-up scans.
Ectopic pregnancy (extrauterine)
From about 5–6 weeks' gestation: one-sided severe pain, dizziness, sometimes sudden heavy bleeding. Life-threatening if rupture occurs. Seek immediate assessment. See guideline: NICE NG126.
Miscarriage (pregnancy loss)
Increasing bleeding, cramp-like pain, possibly passage of tissue. Diagnosis by ultrasound and serial hCG. Patient information: RCOG.
Placental complications (2nd/3rd trimester)
Placenta praevia: painless, fresh bright-red bleeding. Placental abruption: usually pain with a hard abdomen. Late bleeding is always a reason to attend hospital. Overview: NHS.
Frequency by trimester
| Trimester | Typical causes | Assessment |
|---|---|---|
| 1st trimester (0–12 weeks' gestation) | Implantation, hormonal withdrawal bleeding, contact bleeding, subchorionic haematoma, ectopic pregnancy, miscarriage | Light bleeding is common; always discuss with a clinician. |
| 2nd trimester (13–27 weeks' gestation) | Less common; assessment focuses on placental location (praevia), cervical length, infections | Fresh bleeding should be evaluated (clinic/hospital). |
| 3rd trimester (28–40 weeks' gestation) | Placenta praevia, placental abruption, vasa praevia, bloody show as sign of labour | Fresh bleeding can be serious — go to hospital immediately, especially with pain or dizziness. |
Diagnostics: what answers what?
- Transvaginal ultrasound: position of gestational sac/embryo, fetal heart activity, placental location, haematomas.
- Serial hCG & progesterone: trends to distinguish a viable from a failing pregnancy.
- Vaginal swab: detect BV/yeast, with targeted therapy where needed.
- Blood group & rhesus factor: For Rh D negative women, anti‑D prophylaxis may be indicated depending on the situation (after bleeding/trauma/procedures — see guidelines).
Diagnostic pathways: NICE NG126. Concise patient information: RCOG and NHS.
Self-care & behaviour until assessment
- Observe: note colour, amount, duration and accompanying symptoms (pain, fever, dizziness).
- Pads instead of tampons/cup: hygienic and allows better assessment of blood loss.
- Rest: avoid vaginal sex and heavy lifting for now; reduce stress.
- Medications: painkillers only after advice; fever and severe pain are warning signs.
Go to hospital immediately – these signs are an emergency
- heavy fresh bleeding or circulatory symptoms (dizziness, fainting, cold sweat)
- one-sided severe abdominal/shoulder pain (suspected ectopic pregnancy)
- bright red bleeding in the 2nd/3rd trimester, even without pain (placenta praevia)
- painful bleeding with a hard abdomen (placental abruption)
- fever or foul-smelling discharge
Conclusion
In pregnancy: no true menstrual period — but bleeding can occur. Light spotting can be harmless; fresh bright-red or heavy bleeding is a warning sign. Observe colour and amount, rest, use pads and have bleeding assessed by a clinician without delay. With pain, dizziness or late pregnancy bleeding: go to hospital immediately.
