In a natural cycle, only one egg is selected to be grown by a hormone called follicle stimulating hormone (FSH). The egg grows and matures over the next 10-14 days before being released by Luteinising hormone (LH). All the other available eggs that month just die and are wasted.
Research has shown that, for IVF treatment to have a good chance of success, more than one egg is needed. IVF success rates increase as more eggs are collected (to a maximum of 15 eggs, with no further rise in the chances of success above this number). That’s why, during an IVF cycle, the ovaries are stimulated with daily hormone injections of FSH alone or with LH.
The eggs develop in tiny sacs of fluid within the ovaries called follicles. Their growth is carefully monitored over the next 10-14 days using ultrasound scans. This ensures the eggs are harvested at just the right time.