Absent menstruation means no menstrual flow, or period. Absent menstruation may be:

• Primary -- no menstruation before age 16
• 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 healthy females begin to menstruate later than most (the average age is about 13).

Pregnancy is often the first thought when a period is missed, but there are many reasons for having a late period. The rate of primary amenorrhea in the United States is less than 1%. The rate 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:

• 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
• Cyclic pain without bleeding

Causes of primary amenorrhea:

• Delay may be normal if puberty characteristics, such as breast 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 or pituitary 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
• Significant weight gain or obesity
• Hormonal imbalance (such as with polycystic ovarian syndrome)
• Endocrine disorders such as thyroid disease or pituitary disease/tumor
• IUD use
• Too much exercise
• Premature ovarian failure
• Menopause (normal for women over age 45)
• Use of birth control pills and other contraceptives
• Uterine scarring, usually from procedures such as dilation and curettage (D and C)