menarhe

Menarhe, or menarche, is the first menstrual period in humans and marks the start of reproductive capability. It results from the maturation of the hypothalamic–pituitary–ovarian axis during puberty, leading to cyclic hormonal changes and the onset of menstruation.

The timing of menarhe varies widely. Most girls have their first period between ages 10 and 15, with a typical median around 12–13 years. It can occur earlier or later in some individuals. Before the first period, other puberty signs such as breast development and a growth spurt may be present. The initial cycles are often irregular and may be anovulatory, meaning that ovulation does not occur every cycle. Over the next one to two years, regularity and ovulation usually become more consistent.

Several factors influence the timing of menarhe. Genetics play a major role, and physical factors such as body mass index, nutrition, and overall health affect when puberty begins. Environmental and lifestyle factors, including physical activity levels and chronic illness, can also influence timing. In some populations, higher body weight is associated with earlier onset, while very low body weight or malnutrition can delay it.

Variations and concerns: primary delay is when puberty does not begin by about age 13 with other secondary sexual characteristics, or by age 15 without menarche; secondary amenorrhea is the absence of menstruation after its onset for several months and may require medical evaluation. If there are concerns about development, irregular or absent periods, or symptoms such as severe pain or heavy bleeding, a healthcare professional should be consulted. Regular menstrual tracking can help assess normal patterns as puberty progresses.