This ends up creating that higher level of estrogen when compared to progesterone, even though both hormones are in decline. What’s bad about that is that these two hormones are supposed to keep each other in check.
For example, while estrogen proliferates the endometrium, progesterone inhibits its growth. The endometrium is the lining of the uterine walls and it's needed during pregnancy to allow the embryo to grow. Too little endometrial growth and you can have a difficult time getting or staying pregnant. Too much and you can end up with endometriosis and a higher risk for endometrial cancer.
Another example is that while estrogen aids in the development of breast tissue, progesterone keeps that growth in check so you don’t end up developing fibroids and cysts. And while estrogen promotes fluid retention, progesterone is a natural diuretic.