What characterizes the luteal phase of the menstrual cycle?

The luteal phase of the menstrual cycle is characterized by the formation of the corpus luteum, which occurs following ovulation. After an ovary releases an egg, the leftover follicle transforms into the corpus luteum, a structure that plays a crucial role in regulating the menstrual cycle and maintaining early pregnancy. This structure produces progesterone and some estrogen, which are essential for preparing the endometrium for a potential implantation of a fertilized egg.

During this phase, the body is geared towards supporting a possible pregnancy. If the egg is fertilized, the corpus luteum continues to produce hormones until the placenta can take over; without fertilization, the corpus luteum eventually degenerates. The hormonal changes during this phase are significant because they prevent the shedding of the endometrial lining and help maintain the uterine environment.

Considering the other choices, peak estrogen levels primarily occur during the follicular phase just before ovulation, not during the luteal phase. Shedding of the endometrial lining marks the transition into the menstrual phase, which occurs if fertilization does not happen, representing the end of the luteal phase. Ovulation itself occurs prior to the luteal phase, marking the transition from the follicular phase to the luteal phase.