Amenorrhea
Absence of menstruation in a female of reproductive age.
Amenorrhea, also spelled amenorrhoea, refers to the lack of menstrual periods in a female who has reached reproductive age. This condition is a normal, physiological state during pregnancy and breastfeeding. In humans, it describes a woman or girl of reproductive age who is not using birth control yet does not menstruate.
As a symptom rather than a disease itself, amenorrhea has numerous possible causes. It is divided into two categories: primary and secondary. Primary amenorrhea is diagnosed when a girl has not developed secondary sexual characteristics by age 14 and has not had her first period, or when she has normal secondary sexual characteristics but no menstruation by age 16. Causes can include developmental issues, such as a congenital absence of the uterus, ovarian failure or gonadal dysgenesis, or a delay in puberty. Secondary amenorrhea, the cessation of cycles after menstruation has begun, is defined as no period for three months in someone with previously regular cycles, or six months in someone with a history of irregular periods. Common triggers include hormonal disturbances originating in the hypothalamus or pituitary gland, premature menopause, scarring inside the uterus, or eating disorders.
**Pathophysiology** While many factors can lead to amenorrhea, the root cause is always either a hormonal imbalance or a structural abnormality. Normally, the hypothalamus releases gonadotropin-releasing hormone (GnRH), which signals the pituitary to release follicle-stimulating hormone (FSH) and luteinizing hormone (LH). These hormones then stimulate the ovaries to produce estrogen and progesterone, which control the proliferative and secretory phases of the menstrual cycle. Prolactin also plays a role by suppressing LH and FSH release. Thyroid hormone influences the cycle as well; low thyroid levels trigger the hypothalamus to release TRH, which raises both TSH and prolactin. The extra prolactin then suppresses LH and FSH through negative feedback. Any disruption to this hypothalamic-pituitary-ovarian axis—whether from hormonal imbalance or broken feedback loops—can cause amenorrhea.
**Classification** Amenorrhea is sorted into primary or secondary types.
**Primary amenorrhea** Primary amenorrhea means a woman has not started menstruating by age 16.
- Field
- Medicine, Reproductive Endocrinology
- Classification
- Primary and Secondary
- Primary definition
- Absence of menstruation by age 16, or by age 14 with no secondary sexual characteristics
- Secondary definition
- Absence of menses for 3 months (regular cycles) or 6 months (irregular cycles)
- Common physiological causes
- Pregnancy, lactation, menopause
- Common pathological causes
- Turner syndrome, MRKH syndrome, PCOS, thyroid disorders, hypothalamic amenorrhea
Lore & Background
Amenorrhea is classified as primary or secondary. Primary amenorrhea is the absence of menstruation in a woman by age 16, or by age 14 if no secondary sexual characteristics are present. Causes include Turner syndrome (monosomy 45XO), which leads to ovarian insufficiency and gonadal dysgenesis, and Mayer–Rokitansky–Küster–Hauser (MRKH) syndrome, characterized by Müllerian agenesis resulting in absence of a uterus and cervix despite functioning ovaries. Constitutional delay of puberty is a diagnosis of exclusion considered a variant of the normal timeline.
Reader's Guide
Secondary amenorrhea is defined as absence of menses for three months in a woman with previously normal menstruation, or six months in a woman with a history of oligomenorrhea. Causes include hormonal disturbances from the hypothalamus and pituitary gland, premature menopause, intrauterine scar formation, eating disorders, thyroid diseases (hypothyroidism and hyperthyroidism), hyperprolactinemia, polycystic ovary syndrome (PCOS), and functional hypothalamic amenorrhea due to stress, weight loss, or excessive exercise. Lactational amenorrhea, caused by elevated prolactin suppressing LH and FSH, is a common physiologic cause. The condition is significant as a symptom of underlying disorders affecting the hypothalamic-pituitary-ovarian axis, and its management depends on identifying and treating the root cause.
Did You Know?
- Physiological amenorrhea occurs during pregnancy, lactation, and after menopause.
- Turner syndrome, caused by a missing or partially missing X chromosome, often leads to primary amenorrhea due to ovarian insufficiency.
- MRKH syndrome is the second-most common cause of primary amenorrhea and involves absence of the uterus and cervix.
- Functional hypothalamic amenorrhea can be triggered by stress, weight loss, or excessive exercise due to low energy availability.
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