• Dr Peter Chew

Is passing blood clots during menstruation normal? What are the common underlying causes?

Updated: Oct 22, 2019

Normal menstruation is the result of the shedding of the lining of the womb (endometrium) together with the blood. To facilitate the flow, anticoagulants are released by the body to keep the menstrual blood thin and fluid. If the menses are heavy and the blood is expelled too quickly, anticoagulants do not have enough time to work. As a result, blood clots will form. These clots are usually bright red or dark in colour. They are often released on the heavy days of menses and make the menstrual blood look thick.

Occasional blood clots during menstruation is normal and is not a cause for concern. However, if this occurs repeatedly and is accompanied with heavy bleeding, severe anaemia, where there is a lack of oxygen carrying red blood cells may result. Some women are so accustomed to heavy menses that they may not notice the severity of the condition. Over time, excessive blood loss may lead to weakness , fatigue ,heart failure and even death. Thus, it is important to find out the underlying cause so that appropriate treatment can be given immediately.

Common causes include:

• Hormonal imbalance. In a normal menstrual cycle, there is a balance between two hormones-- oestrogen and progesterone --secreted by the ovary. These hormones regulate the growth of the endometrium. If hormonal imbalance occurs from irregular or defective ovulation, endometrium may grow in excess and shed by way of heavy bleeding.

• Uterine fibroids. These are muscle growths of the womb. They can cause heavy or prolonged menstrual bleeding by increasing the surface area of the endometrium.

• Adenomyosis. This occurs when the glands from the endometrium become embedded in the uterine muscle, causing enlargement of the uterine cavity and thus the bleeding surface.

• Endometriosis: This is due to the backflow of the menstrual blood into the pelvis.

• Chronic pelvic infection: This usually results from sexually transmitted diseases

• Polyps: These are small, non-cancerous growths on the endometrium.

• Intrauterine device (IUD). Heavy menses is a side effect of the non-hormonal intrauterine contraceptive device.

• Cancer. Uterine cancer, ovarian cancer and cervical cancer can cause excessive menstrual bleeding.

• Other medical conditions including thyroid problems, bleeding disorders, liver and kidney diseases may be associated with heavy menses


Appropriate treatment is given depending on the cause of the bleeding and its severity. It may include the following


• Iron supplements with multivitamins to correct the anaemia

• Pain killers, tranexamic acid and oral contraceptive pills have been used to reduce blood clots

2.Insertion of Mirena, an intrauterine contraceptive device (IUCD) impregnated with progesterone. The hormone will reduce the thickness of endometrium.

3.Surgical Treatment

• Dilatation and Curettage (D&C ): This will remove the endometrium for microscopic examination.

• Hysteroscopy. A surgical procedure when a telescope is introduced into the womb to remove polyps and fibroids

• Endometrial ablation or resection using hysteroscope to burn off or remove whole or part of the endometrium.

• Hysterectomy. This involves removing the entire womb surgically.

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