The American Academy of Pediatrics reports that once a girl reaches menarche, it takes time for her body to adjust to becoming fully ovulatory. It is normal for girls in early adolescence to have cycles ranging from 21 to 45 days and even 90 day cycles are not uncommon. Girls should consult a physician when they skip more than 90 days between periods.
Obesity, Estrogen Dominance and Polycystic Ovarian Syndrome
Women who have a body mass index (BMI) higher than 30 are considered obese and are at risk of developing amenorrhea. Obesity can cause excess estrogen production. Too much estrogen in the body can upset the normal ratio of estrogen to progesterone and lead to delayed menstrual cycles.
Fifty percent of women who have Polycystic Ovarian Syndrome (PCOS) are obese. Women with PCOS suffer from excess body hair, insulin resistance, ovarian cysts, infertility, high androgen levels and menstrual abnormalities.
Pregnancy and Lactation
Any woman of reproductive age should see her doctor as soon as she skips a period to determine if she is pregnant and to obtain prenatal care if she tests positive for pregnancy.
Lactation is one of the common causes of missed periods. When a baby suckles at his mother’s breast, chemical signals pass between the mother’s nipples and her brain which suppress the gonadotrophin-releasing hormone (GnRH) responsible for follicle and egg maturation in the ovaries.
According to the World Health Organization, this natural method for suppressing fertility is 98.8 to 98.1 percent effective if women breastfeed their infant every four to six hours and do not supplement their milk supply with either water or infant formula.
Prescription Medications and Illicit Drugs
According to Mayo Clinic, medicines such as "antidepressants, antipsychotics, some chemotherapy drugs and oral corticosteroids can cause amenorrhea."
Opiate abuse can lead to missed periods. According to the American Journal of Obstetrics and Gynecology, approximately 20 percent of female heroin addicts suffer from amenorrhea. Methadone use can also disrupt normal menstrual cycles.
Bulimia and Anorexia are common causes of missed periods because of hormonal imbalances brought on by low body weight.
Perimenopause and Menopause
Perimenopause is the time period preceding menopause, which typically lasts 5 to 10 years prior to menopause. Missed periods are common during perimenopause due to a gradual decrease of estrogen and egg production in the body.
The average age of menopause begins at age 51 in the United States. Menopause is defined as the complete cessation of menstrual periods for one year.