What Are the Causes of a Late Menstrual Cycle?

There are some women who can practically set their watches by the e timing of their menstrual periods. However, for a majority of women, it is not uncommon for a cycle to be late or even completely absent. There are many potential causes of delayed menstruation, and only a doctor or nurse-midwife can accurately diagnose the underlying cause. A late menstrual period is only rarely a sign of a serious medical condition.

Pregnancy

• For women who generally experience regular menstrual cycles, pregnancy is by far the most common cause of a late period. If a woman is sexually active and experiencing delayed menstruation, it is likely that she is pregnant--especially if there is no other known reason for the delay.
  Home pregnancy tests are available at most drug stores and pharmacies to confirm this possibility. A blastocyst has already implanted and begun producing HCG, the "pregnancy hormone," by the time a period is noticeably late, so tests taken after this time are generally accurate. Women who are pregnant, or believe they may be pregnant, should speak with a doctor or midwife for further counseling and care.

Breastfeeding

• Women who are nursing may experience absent or delayed menstrual periods for the entire duration of breastfeeding, and this is especially common during the first few months after giving birth. Breastfeeding mothers may experience absent, shortened, late or unusually light menstrual periods.
  Breastfeeding usually prevents ovulation for at least the first six months, and women who are nursing are less likely to become pregnant because of this. However, many breastfeeding mothers will ovulate before the return of regular menstrual periods. Though delayed menstruation during breastfeeding is common, sexually active women who are nursing should still consider the possibility that they may be pregnant if a period does not arrive "on time."

Medication

• Many drugs and medications can result in abnormal or delayed menstrual cycles. Most notably, hormonal contraceptives can cause a period to be absent or late. Contraceptives that affect estrogen and/or progesterone levels, including the combination pill, minipill, patch and shot, may cause a delay in menstruation. Progesterone-containing IUDs, like Mirena, may have the same effect.
  Other drugs may also have a noticeable effect on menstrual cycles. Corticosteroids and chemotherapy drugs often delay menstruation, and some types of antidepressants and antipsychotics will also suppress the menstrual cycle.

Low Body Fat

• Estrogen levels directly relate to the amount of fat stored in the body. While women with high body fat levels are likely to experience frequent or prolonged menstrual periods, women with very little body fat are likely to experience menstruation irregularly or infrequently. Women who are underweight due to disease--such as anorexia nervosa, hyperthyroidism or inflammatory bowel disease--are especially likely to experience amenorrhea.
  Less commonly, very athletic women may experience late menstrual periods as a result of having low levels of body fat. Additionally, factors such as stress and high caloric expenditure can contribute to the absence or delay of menstruation. Athletes may be especially prone to these situations.

Hormone Shifts

• Many different hormone imbalances can cause delayed menstruation. One of the most common is polycystic ovary syndrome, or PCOS. Other hormone-affecting conditions, like thyroid disease and malfunction of the pituitary gland, can also cause menstrual periods to be absent or unpredictable.
  Menopause is also a common cause of delayed or absent menstruation, and should be considered as a potential causative factor if the woman is also experiencing other menopausal symptoms, or is an appropriate age for the "change of life" to occur. Women experiencing menopause-like symptoms prior to age 40 may be suffering from premature menopause, and should seek medical consultation.