The absence of menstruation means no menstrual flow. Absent menstruation may be primary (no menstruation before age 16) or secondary (menstruation begins at the appropriate age, but later stops for more than 3 cycles or 6 months).

Absent menstruation is called amenorrhea.

Many perfectly normal females begin to menstruate later than most (the median age is 12.8).

Pregnancy is often the first thought when a period is missed, but there are many reasons for having a late period.

The incidence of primary amenorrhea in the United States is less than 1%. The incidence of secondary amenorrhea (due to some cause other than pregnancy) is about 4% in the general population.

Symptoms associated with amenorrhea depend on the cause and may include the following:

• Headache
• Galactorrhea (breasts produce milk in a woman who is not pregnant or breast-feeding an infant)
• Visual loss (in rare cases of pituitary tumor)
• Marked weight gain or weight loss
• Dry vagina
• Increased hair growth in a "male" pattern (hirsutism)
• Voice changes
• Breast size changes

Causes of primary amenorrhea:

• Delay may be normal if puberty characteristics, such as breat development, are present by age 13
• Birth defects of the female reproductive system
• Lack of an opening in the membrane at the entrance of the vagina (hymen)
• Problem with the hypothalamus gland

Factors that can disrupt normal menstruation include:

• Drastic weight reduction
• Eating disorders
• Stress

Causes of secondary amenorrhea:

• Pregnancy
• Stress and anxiety
• Drastic weight reduction
• Hormonal imbalance (such as with polycystic ovarian syndrome)
• Endocrine disorders such as thyroid disease or pituitary disease/tumor
• Other illness
• Excessive exercise
• Menopause (normal for women over age 45)
• Medications, including birth control pills and other contraceptives
• Uterine scarring, usually from procedures such as dilation and curettage (D and C)

Treatment depends on the cause.

• For amenorrhea caused by normal delay of menstruation onset, have patience until age 16. However, keep in mind that the delay is only normal if the girl displays some signs of puberty, such as breast development
• Consult your obstetrician to determine if you may be pregnant.
• For a missed period caused by drastic weight loss or obesity, proper diet is recommended.
• For a missed period resulting from excessive exercise, cut back to a more conservative workout program.