Quick Answer
The average amount of blood loss during a normal period is 30-40 ml. However, anything from 5 ml to 80 ml can be considered normal. Heavy menstrual bleeding, also known as menorrhagia, is defined as losing 80 ml or more of blood per cycle.
What is Considered a Normal Amount of Blood Loss During a Period?
During a normal menstrual cycle, the average woman loses around 30-40 ml of blood over 3-5 days. However, there is a wide range of what is considered normal:
- Light: less than 20 ml per cycle
- Moderate: 20-60 ml per cycle
- Heavy: 80-250 ml per cycle
Losing under 5 ml of blood during your period is very light and may indicate an underlying problem like excessive exercise, eating disorder, or hormonal imbalance. Losing over 80 ml per cycle is considered heavy menstrual bleeding.
How is Menstrual Blood Loss Measured?
While it may seem difficult to measure monthly blood loss, doctors have several methods to estimate the amount of menstrual bleeding:
- Weighing pads/tampons before and after use
- Hemoglobin testing to check for anemia
- Alkaline hematin method to extract heme from used pads/tampons
- Pictorial blood loss assessment chart (PBAC)
The PBAC is commonly used in clinical practice. It assigns points based on the number of pads and tampons used per day and appearance of the blood. A score above 100 indicates heavy bleeding. For precise measurement, the alkaline hematin method is considered the gold standard.
What Affects Blood Flow During Periods?
The amount of menstrual blood loss can vary each cycle and is affected by various factors:
- Age – Blood loss is heavier in the first years after menarche and again leading up to menopause.
- Birth control – Hormonal methods like the pill can decrease flow.
- Pregnancy – Periods are lighter during pregnancy and breastfeeding.
- Medications – Blood thinners and anti-inflammatories may increase bleeding.
- Medical conditions – Fibroids, endometriosis, thyroid disorders, etc. can lead to heavy periods.
If your blood flow changes suddenly or falls outside the normal range, see your doctor to identify any underlying causes.
Is it Normal to Clot During Your Period?
It is very common to pass blood clots during menstruation. In fact, most women will experience clotting at some point.
When the uterine lining sheds, that tissue and blood can coagulate inside the uterus or vagina to form clots. This is a normal part of the menstrual process. Clots typically vary in size from small flecks to clumps the size of a quarter.
As long as the clots are not very large (over 1 inch) or accompanied by heavy flow, clotting is usually not a major concern. However, passing many large clots or long, ropey clots could indicate a problem and should be evaluated by your gynecologist.
What Causes Clotting During Periods?
Menstrual clots form when anticoagulants are unable to break down blood as quickly as it is shed. Factors that can increase clotting include:
- Heavy flow – More blood means faster shedding which can lead to clumps.
- Thick uterine lining – A thicker endometrium may shed in larger pieces.
- Retrograde flow – Blood flowing back into the uterus can pool and coagulate.
- Fibroids – These noncancerous growths disrupt smooth muscle contraction.
- Adenomyosis – This condition thickens the uterine lining.
Clots may be slightly more common just after starting your period when flow is heaviest. They tend to decrease once the flow lightens up.
When to See Your Doctor About Clots
Occasional small clots are normal, but you should make an appointment with your doctor if you experience:
- Clots over 1 inch in size
- Needing to change pads every hour from passing clots
- Long, ropy clots
- Severe pain and cramping with clots
- Clots accompanied by foul odor
- Clotting that persists throughout your period
- Feeling lightheaded or dizzy passing clots
This can indicate a condition like endometriosis, uterine fibroids, or an underlying bleeding disorder that requires treatment.
What Is Considered Heavy Menstrual Bleeding?
Heavy menstrual bleeding, also called menorrhagia, is defined as losing over 80 ml of blood per menstrual cycle. It affects 10-15% of women.
The most common symptoms of heavy periods include:
- Bleeding that soaks through one or more pad/tampon every hour for multiple hours
- Needing to use double sanitary protection – both pad and tampon
- Passing large blood clots
- Bleeding that lasts longer than 7 days
- Low iron levels causing fatigue and shortness of breath
Heavy flow that continues for multiple cycles is not normal and can negatively impact your quality of life. Make an appointment with your doctor so the cause can be identified and treated.
What Causes Heavy Menstrual Bleeding?
Some potential causes of abnormally heavy periods include:
- Uterine fibroids – noncancerous growths in the uterus
- Endometriosis – uterine tissue growing outside the uterus
- Adenomyosis – tissue growing into the uterine wall
- Hormone imbalance – issues with estrogen and progesterone
- IUDs – copper IUDs can increase menstrual flow
- Pregnancy complications – miscarriage or ectopic pregnancy
- Clotting disorders – von Willebrand disease or platelet dysfunction
- Thyroid disease
- Pelvic infections
- Polyps or other anatomical anomalies
In some cases, no underlying cause is found. Doctors refer to this as dysfunctional uterine bleeding. Once pregnancy complications are ruled out, a pelvic exam and ultrasound are usually the first approaches to identify potential problems. Further blood testing might include checking thyroid, platelet, and hormone levels.
Treatments for Heavy Menstrual Bleeding
Treatments for heavy periods depend on the underlying cause, your age, and whether you hope to get pregnant in the future. Options include:
- Hormonal birth control – oral contraceptives and the hormonal IUD Mirena can lighten flow.
- Tranexamic acid – non-hormonal medication that controls bleeding.
- NSAIDs – helps reduce flow from prostaglandin inhibition.
- Endometrial ablation – destroys the uterine lining to reduce bleeding.
- Uterine artery embolization – blocks blood flow to fibroids.
- Myomectomy – surgical removal of fibroids.
- Hysterectomy – surgical removal of the uterus.
Make sure to follow up regularly with your doctor to monitor treatment efficacy and whether any adjustments need to be made.
When to See a Doctor for Heavy Menstrual Bleeding
You should make an appointment with your doctor if you experience any of the following:
- Bleeding longer than 7 days
- Bleeding or passing clots so heavily that you need to change protection every 1-2 hours
- Feeling dizzy or lightheaded during your period
- Severe pain or cramping that interferes with normal activities
- Bleeding between periods or after intercourse
- Periods that stop you from participating in sports, work, or social events
Heavy bleeding that occurs one or two times can usually be managed with medication. But if it persists for multiple cycles, you need to identify the underlying cause. Ignoring very heavy menstrual bleeding can result in iron deficiency anemia over time.
Seek prompt emergency care if you experience bleeding plus:
- Severe abdominal pain
- Fever and chills
- Fainting
This may indicate a more serious condition requiring immediate treatment.
Conclusion
The average menstrual blood loss per cycle is around 30-40 ml. However, normal can range from 5 ml up to 80 ml. Heavier bleeding is common in adolescence and perimenopause and can also result from hormonal issues, fibroids, polyps, and other medical conditions.
While small clots are very common, large clots over 1 inch or persistent heavy bleeding for multiple cycles is not normal. This guide covered the key indicators of when you need to see a doctor about heavy periods or abnormal clotting. Identifying and treating any underlying problem is important to prevent complications like anemia down the road.
