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There are two main ways to classify amenorrhea, one is by the cause and the other is by the function. The cause can be either primary or secondary, while the function refers to the type of hormones that are involved in the absence of menstruation. Both of these categorizations of types of amenorrhea are discussed in more detail below.
Primary amenorrhea involves the absence of menarche in a woman aged 16 years. The menarche is the first menstrual cycle or the first menstrual bleeding that a women experiences, which varies by factors, such as ethnicity, geographic region and other characteristics. Primary amenorrhea may present due to conditions such as:
Secondary amenorrhea involves the cessation of menstruation in a woman who previously had a regular menstrual cycle. Three months or more without a menstrual period in a woman is the definition of amenorrhea. This occurs most often in women who are pregnant, breastfeeding or approaching menopause (between 40 and 55 years of age).
However, there are various other causes of secondary amenorrhea, including Asherman’s syndrome, strenuous physical activity and low body weight. These may affect a woman of any age and, for this reason, can lead to amenorrhea in a woman who previously had a regular menstrual cycle.
The reproductive axis can be divided into the functional compartments:
In outflow-type amenorrhea, the hypothalamic-pituitary-ovarian axis functions as normal, with regular hormonal levels, but there is some malfunction of the uterus, cervix or vagina. This may include causative conditions such as Müllerian agenesis, vaginal atresia, cryptomenorrhea, imperforate hymen and Asherman’s syndrome.
In gonadal-type amenorrhea, the ovaries do not respond to the hormones secreted from the hypothalamic-pituitary axis as normal. It is associated with low levels of estrogen and high levels of follicle stimulating hormone (FSH) and requires treatment. Conditions that may cause this type of amenorrhea include:
In regulatory-type amenorrhea, the pituitary gland or the hypothalamus has an altered function, which affects the levels of sexual hormones and their effects in the body. Abnormal levels of gonadotropin hormones can lead to amenorrhea due to the effects of hypogonadotropic, eugonadotropic or hypergonadotropic conditions on the levels of follicle stimulating hormone (FSH). Conditions associated with this type of amenorrhea include Kallmann syndrome, Sheehan syndrome, abnormal thyroid function and excessive physical stress.
The classification by function is the most useful in the treatment of amenorrhea, as this is indicative of where the problem originates and which areas should be targeted in treatment. For example, hormonal therapy plays a large role in the treatment of regulatory-type amenorrhea, but it is not necessary for outflow-type amenorrhea, because hormone levels are usually normal.