In vitro maturation (IVM) is the technique of letting ovarian follicles mature in vitro.
Techniques available 
The ability of in IVM depends on how mature the follicle already is. There are several stages in folliculogenesis, starting with a primordial follicle, which then becomes a primary, secondary, early tertiary (antral), late tertiary and eventually a preovulatory follicle. If a follicle has reached the early tertiary or antral stage, IVM can be carried out. A few live births have already been made by taking small early tertiary follicles, letting them mature in vitro and subsequently fertilizing them. However, for follicles that haven't reached the early tertiary stage, IVM is still under development. There are a lot of cellular changes in the oocyte and the rest of the cells in the follicle, which makes it very susceptible. Nevertheless, it is possible to let a primordial follicle mature to a secondary follicle outside the body by growing it in a slice of ovarian tissue. The subsequent maturity from secondary to early tertiary stage can then be supported in test-tubes.
IVM can be expanded with hCG-priming, which is exposing the ovarian tissue to human chorionic gonadotropin (hCG). This results in an expanding or dispersed pattern of the cumulus oophorus around the egg cell, facilitating its identification within follicular fluid. However, the evidence of a clinical effect of hCG priming is still lacking. IVM can also be expanded with intracytoplasmic sperm injection (ICSI), which should be performed at least one hour (and optimally two to four hours) after the first polar body extrusion.
- Facilitate IVF, and provide an alternative to ovulation induction. Before an IVF, an ovarian hyperstimulation is usually performed. By injecting gonadotropins, multiple oocytes will mature. Similar methods are applied in ovulation induction for other purposes. However, with IVM, injection of gonadotropins into the body isn't essential. Rather, oocytes can mature outside the body, such as prior to IVF. However, there still isn't enough evidence to prove the effectiveness and security of the technique.
- For research. There are a million of oocytes in the ovary at birth, but only about 400 of these will be ovulated. The rest will die by Ovarian follicle atresia. When oocytes destined to die are extracted, IVM enables the maturation of these follicles. Thus, they can be studied to gather more information on folliculogenesis and oocyte maturation.