Epidemiological evidence points to the significant reduction in the possibility of pregnancy with reduced duration of the follicular phase, supporting the existence of term maturation.
As we have already learned, variations in the duration of the menstrual cycle are determined by the duration of the follicular phase. This is why when we see changes in the duration of the menstrual cycle, we can safely assume that it is solely due to the changes in the follicular phase. As you can see from the graph below, when the follicular phase shortens by only 3-4 days, the fecundity (ability to conceive) in the normally menstruating woman drops in half:
Thus, epidemiological data point to a specific, optimal duration of the follicular phase, when an oocyte is groomed for competency – term maturation.
It must be noted that in a natural cycle, the duration of the follicular phase will also affect the size of the so-called corpus-luteum, which is an independent variable for a viable pregnancy.