What are ovarian follicles?
Ovarian follicles grow inside the ovary and release the egg. The egg released from the female is capable of fertilizing with the sperm and forming an embryo. In young females, follicles in the ovary are not growing and they remain in the sleeping stage. After the start of menstrual cycle, the follicle enters into a periodic growth phase. These fluid-filled sacs in the ovary grow progressively in the early half of the menstrual cycle. Each mature follicle nurtures an egg inside it surrounded by cells called cumulus. In a normal menstrual cycle, many follicles grow but only one can achieve maturity whereas others fade away. In the IVF procedure, many follicles can be grown artificially by hormone injections and they are collected by follicular aspiration. The mature egg is capable of being fertilized by a sperm.
Healthy sperms with good motility are essential to fertilize an egg. Human eggs can't be seen in ultrasound but their follicles are monitored. The eggs can be seen through a microscope.