The absence of menstrual flow, either primary (menstruation fails to begin before age 16) or secondary (menstruation begins at the appropriate age, but later ceases for 6 or more months in the absence of normal causes such as pregnancy, lactation, or menopause).

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.

Increased risk is associated with extreme and prolonged exercise (particularly without adequate conditioning), body fat content less than 15% to 17%, extreme obesity, and taking hormonal supplements.

Symptoms associated with amenorrhea 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, and breast size changes.

PRIMARY AMENORRHEA

• Normal delay of onset (up to age 16)
• Lack of an opening in the membrane at the entrance of the vagina (hymen)
• Drastic weight reduction
• Congenital abnormalities of the genital system
• Chromosomal abnormalities
• Extreme obesity

SECONDARY AMENORRHEA

• Pregnancy
• Anxiety over pregnancy may cause a missed period, thereby increasing the anxiety even further
• Drastic weight reduction
• Vigorous athletics
• Obesity
• Emotional distress
• Menopause (normal for women over age 45)
• Endocrine disorders such as thyroid disease or pituitary disease/tumor
• Drugs such as busulfan, chlorambucil, cyclophosphamide, oral contraceptives, phenothiazines, and non-oral contraceptives (such as Norplant and Depo-Provera)
• Dilation and curettage (D and C)