Menstrual cycle
The recurring hormonal and reproductive changes that prepare the uterus for pregnancy, including ovulation and, without pregnancy, menstruation.
Follicular phase: The first part of the menstrual cycle, when ovarian follicles develop and the uterine lining begins to thicken. Rising estrogen links follicle development to rebuilding the lining after menstruation.
Follicle-stimulating hormone: A pituitary hormone that promotes growth of ovarian follicles and supports estrogen production. Its early-cycle rise helps recruit follicles for that cycle.
Fertility awareness: Methods for estimating fertile and less fertile days by tracking menstrual-cycle signs. Cycle timing and ovulation signs can guide pregnancy planning or avoidance.
Menstrual cycle variability: Differences in cycle length, bleeding, or timing between cycles or among individuals. Variation is common, so a fixed 28-day schedule is not a universal standard.
Pregnancy: The condition in which an embryo or fetus develops in the uterus or, rarely, elsewhere in the reproductive tract. Pregnancy changes hormonal signaling and usually prevents the usual menstrual shedding.
Ovulation: The release of an egg from an ovarian follicle, usually after a surge in luteinizing hormone. This event divides the cycle’s follicular and luteal phases and creates a brief fertile window.
Luteinizing hormone: A pituitary hormone that triggers ovulation and supports formation of the corpus luteum. A sharp mid-cycle surge precipitates release of the egg.
Basal body temperature: The body's resting temperature, which typically rises slightly after ovulation under progesterone’s influence. A sustained temperature shift can help identify ovulation retrospectively.
Amenorrhea: The absence of menstrual bleeding during years when menstruation would otherwise be expected. Missing periods can signal pregnancy, energy imbalance, illness, or other hormonal changes.
Menopause: The permanent end of menstruation after ovarian reproductive function declines, diagnosed retrospectively after twelve months without bleeding. It marks the lasting cessation of menstrual cycles, unlike a skipped period.