In which phase does menstruation typically begin if pregnancy does not occur?

Menstruation typically begins during the luteal phase if pregnancy does not occur. The menstrual cycle can be divided into several phases, with the luteal phase occurring after ovulation. During this phase, the body prepares for a potential pregnancy, with the endometrium thickening due to increased progesterone levels. If fertilization does not happen, hormone levels decline, leading to the shedding of the uterine lining, which results in menstruation. This shedding marks the beginning of the menstrual cycle anew.

In contrast, the follicular phase involves the development of follicles and occurs before ovulation, while the ovulatory phase is when an egg is released from the ovary. The menses phase is actually the bleeding phase of the menstrual cycle, but it does not refer to the phase preceding menstruation following ovulation. Hence, identifying the luteal phase as the correct phase for menstruation onset emphasizes the hormonal changes that influence this critical aspect of the menstrual cycle.