At the time of ovulation, the normal size of the follicle is between 1.8 and 2.5 cm, which is the more mature follicle. When a woman is menstruating, new follicles are growing on the surface of the ovary and most will have multiple small follicles present. With the ovary secreting estrogen, only one dominant follicle will grow and develop and will grow to maturity at the time of ovulation and therefore ovulation will occur under the influence of hormone levels. If the ovary has multiple follicles, all of which are small and without mature follicles, this may lead to a pathological condition such as polycystic ovary syndrome, in which even if there is sex, the woman may not get pregnant because the eggs are not expelled. Women can monitor their chances of pregnancy by ovulation test or ultrasound when the follicles are mature.