Menstrual Cycle: An Overview

The Menstrual Cycle: An Overview

Illustration demonstrating the menstrual cycle

What is ovulation?

When a young woman reaches puberty,
she starts to ovulate. This is when a mature egg or ovum is released from one of the
ovaries. The ovaries are the two female reproductive organs found in the pelvis. If
egg is fertilized by a sperm as it travels down the fallopian tube, then pregnancy
occurs. The fertilized egg attaches to the lining of the uterus. The placenta then
develops. The placenta transfers nutrition and oxygen to the fetus from mother. If
egg doesn’t become fertilized, the lining of the uterus (endometrium) is shed during

The average menstrual cycle lasts
28 days. The cycle starts with the first day of one period and ends with the first
of the next period. The average woman ovulates on day 14. At this time, some women have
minor discomfort in their lower abdomen, spotting, or bleeding, while others don’t have
any symptoms at all.

A woman is generally most likely to
get pregnant (be fertile) if she has sex a few days before, and during ovulation.

What is menstruation?

Menstruation is one part of a
woman’s cycle when the lining of the uterus (endometrium) is shed. This occurs
throughout a woman’s reproductive life. With each monthly cycle, the endometrium
prepares itself to nourish a fetus. Increased levels of estrogen and progesterone
thicken its walls. If fertilization doesn’t occur, the endometrium, along with blood
mucus from the vagina and cervix make up the menstrual flow that leaves the body through
the vagina during the period.

When does menstruation start?

On average, a young woman in the
U.S. has her first menstrual period at about age 12. This is generally 2 to 3 years
after her breasts start to grow. This is also soon after she notices pubic and underarm
hair. Stress, strenuous exercise, and diet can affect when a girl first has her

The American College of
Obstetricians and Gynecologists recommends that a young woman consult her healthcare
provider if she has not started to menstruate by the age of 15, or if she has not
to develop breast buds, pubic hair, or underarm hair by the age of 13.

How long is a menstrual cycle?

For menstruating women, an average
menstrual cycle lasts 28 days. It starts with the first day of the last period and
with the first day of the next menstrual period. However, the length of women’s cycles
varies, particularly for the first year or 2 after a young woman has her first period.
Women may have cycles as short as 21 days, or as long as 45 days during the first
years. However, anything outside of this range may require medical attention.