Women experience menstrual cycles that occur approximately every 28 days. This cycle is controlled by hormones and results in the shedding of the uterine lining, or menstruation, commonly known as a period. But what exactly is your period made of?
The Menstrual Cycle
The menstrual cycle starts on the first day of your period, which is known as day 1. It continues until the first day of your next period. The cycle has different phases that are controlled by hormones:
- Follicular phase – Usually lasts 14 days. Estrogen levels rise and mature an egg in one of the ovaries. The uterine lining thickens in preparation for pregnancy.
- Ovulation – Around day 14 of a 28 day cycle. The mature egg is released from the ovary. This is the fertile window.
- Luteal phase – Usually lasts 14 days. If pregnancy does not occur, progesterone levels drop, signaling the uterus to shed its lining. This is menstruation.
The entire process takes about 28 days, but can vary from 21-35 days and still be considered normal. Now let’s look at what exactly is shed each month during your period.
The Uterine Lining
The uterine lining, also called the endometrium, builds up during the first half of the menstrual cycle. This provides a place for a fertilized egg to implant and grow. It contains:
- Blood vessels – Supply blood to the developing fetus.
- Glands – Secrete nutrients to nourish the embryo.
- Immune cells – Protect against infections.
- Tissue – Cushions the embryo and expands as the fetus grows.
If pregnancy does not occur, this entire lining is shed during your period. The amount varies between individuals, but on average around 30-40 milliliters of fluid is lost during each menstrual cycle.
Menstrual Fluid Composition
The menstrual fluid released is more than just blood. Here is what makes up menstrual fluid:
- Blood – Composed of red blood cells, white blood cells, platelets and plasma. Makes up around 35-50% of fluid.
- Endometrial cells – The tissue lining the uterus that is shed.
- Cervical mucus – Thick fluid from the cervix that helps flush out tissue.
- Vaginal secretions – Fluid and bacteria from the vagina.
The amount of blood lost varies each cycle and woman to woman. Losing 80 milliliters or more of blood is considered a menorrhagia, or heavy period. The blood provides the red color, while tissue shedding and cervical mucus contribute to the brownish appearance.
Chemical Composition
In addition to the structures that make up menstrual fluid, it contains a variety of chemicals, including:
- Prostaglandins – Cause uterus cramps and contractions to shed the lining.
- Iron – Comes from blood hemoglobin.
- Sodium, calcium, chloride – Electrolytes from blood plasma.
- Protein – Albumin and globulin from blood plasma.
The iron content is around 35 micrograms per gram of menstrual fluid. Estrogen is also present early in the cycle. The specific chemical composition varies day-to-day.
Odor and Color
Menstrual fluid typically has a faint odor caused by:
- Fatty acids from endometrial tissue.
- Changes in vaginal bacteria.
- The iron content breaking down.
This odor is normal, but a particularly foul odor may indicate infection. The color of menstrual fluid can range from bright red to dark brown or black. This depends on:
- Flow rate – Faster flow is more watery and diluted.
- Time since onset – Blood darkens upon exposure to air.
- Presence of tissue – Adds a brownish color.
Darker blood at the beginning or end of your period is normal. But black clots or consistently dark blood could indicate a problem.
Clots and Cramps
Some additional components you may notice in your menstrual fluid include:
- Clots – Thickened blood that coagulates before leaving the body. Up to 1-2 inches is normal.
- Cramps – Caused by contractions of the uterus to expel lining. Prostaglandins intensify the cramps.
- Headaches – Can accompany cramping due to prostaglandin release.
- Irritability – Hormone fluctuations may impact mood.
Moderate to severe cramping that disrupts daily activities should be discussed with your doctor. They can recommend pain relievers and other remedies to ease symptoms.
Variation and Changes
Menstrual flow and composition often varies from adolescent to adulthood. Here are some common changes:
- Heavy, irregular cycles in adolescence
- Lighter, shorter, more regular cycles in adulthood
- Increased or decreased cramps over time
- More clots with heavy flow
- Premenopausal changes in late 30s-40s
Pregnancy, breastfeeding, contraceptives, medical conditions, and other factors can also impact your menstrual cycles. Track your periods to identify variations and discuss concerns with your gynecologist.
When to See a Doctor
See your doctor if you experience:
- Periods lasting longer than 7 days
- Bleeding between periods
- Periods less than 21 days or over 35 days apart
- Sudden increases in flow volume
- Severe pain or cramping
Also discuss any concerns about odor, consistency, color changes or clots with your doctor. They can determine if an underlying condition is causing abnormal changes in your menstrual flow.
Conclusion
In summary, here is what a normal menstrual period contains:
| Component | Details |
|---|---|
| Blood | Makes up 35-50% of fluid volume. Contains red blood cells, white blood cells, platelets, and plasma. |
| Endometrial tissue | Shedding of the uterine lining builds up the menstrual flow. |
| Cervical mucus | Thick fluid that aids in expelling tissue from the cervix. |
| Vaginal secretions | Fluid and bacteria from the vaginal canal. |
| Prostaglandins | Cause uterus contractions and cramping during your period. |
| Clots | Coagulated blood, up to 1-2 inches is normal. |
Menstrual flow varies in amount, duration, odor, color and composition. Track your monthly cycles and discuss abnormal changes with your doctor. This can help identify underlying reproductive or other health conditions.