During an IVF cycle, it is the follicles that are monitored by measuring their diameter with ultrasound.
In each IVF cycle, an egg develops inside a structure called a follicle which is a fluid filled sac that is visible on ultrasound.Once the controlled ovarian hyperstimulation process begins, ultrasound examinations are performed starting after 3 days. They are then repeated every other day and eventually daily so that adjustments in the medication can be made as needed. Along with the ultrasound measurements, blood is drawn at each visit and levels of Estrogen and Progesterone are determined to further allow Dr. Anderson to make the appropriate adjustments.
When the follicle sizes and Estrogen and Progesterone levels indicate that the eggs are mature, an injection of hCG (human chorionic gonadotropin) is given to cause the eggs to release so that they may be removed from the follicles. hCG is used because it is structurally similar to the hormone LH which triggers ovulation in a natural cycle. It is important to give the hCG at the proper time to insure that the eggs release from the ovaries and are fertilizable once retrieved. Careful monitoring is therefore critical to the success of the IVF cycle and should never be replaced with pre-determined protocols designed to maximize convenience.