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In vitro maturation (IVM) of oocytes is an established technique that provides a treatment option for subfertile patients without the risks and costs associate with COH.
In vitro maturation (IVM) of oocytes is an established technique that provides a treatment option for subfertile patients without the risks and costs associated with COH. IVM differs from IVF in two ways: There is no need for COH with exogenous gonadotropins, and oocytes are collected before they attain full maturity. Immature oocytes can resume meiosis in vitro when removed from the meiotically inhibiting environment of the small antral follicles. Collection and IVM of these already existing immature oocytes provide multiple mature oocytes that can be fertilized in vitro.
Both clinical and laboratory aspects of IVM have improved continuously since 1991, when the first live birth following transfer of embryos derived from immature oocytes collected from unstimulated ovaries was reported.
IVM cycle monitoring and management
At the McGill University Health Centre and Montreal Reproductive Centre, IVM cycle monitoring starts with a baseline ultrasound scan performed in the early follicular phase of the menstrual cycle, between days 2 to 5 of a natural menstrual cycle or a withdrawal bleed, induced with the use of a progestogen in amenorrheic women. The aim of the baseline scan is to rule out the presence of an ovarian cyst or uterine pathology and measure the number of antral follicles.
The antral follicle count seems to be the single most important predictor of the number of retrievable oocytes.6 The next scan is performed between days 6 and 8 of the cycle. When the largest follicle reaches 10 mm to 12 mm in diameter and the endometrial thickness is at least 6 mm, a single dose of 10,000 IU human chorionic gonadotropin (HCG) injection is given. Oocyte collection is scheduled at 38 hours after HCG injection.
We have reported that the implantation and clinical pregnancy rates were the highest in cycles when the leading follicle was 12 mm at the day of HCG administration.7 In HCG-primed IVM cycles compared with nonprimed IVM cycles, the rate of oocytes with dispersed cumulus cells was found to be higher, which resulted in higher blastocyst development.5,8,9
When the endometrial thickness is less than 6 mm on the day of the second scan and the leading follicle also is small, we delay HCG administration/oocyte collection. A short course of gonadotropins is added to stimulate the growth of both follicles and the endometrium. We administer 150 IU/day to 300 IU/day of human menopausal gonadotropin to this group of patients. The duration of follicle-stimulating hormone priming depends on the patient's response varying between 3 and 6 days
The key point is to reach the follicle size of 10 mm to 12 mm to yield 1 or 2 mature oocytes on the day of collection, which results in better pregnancy rates.7,9 However, in IVF cycles the aim is to reach an 18-mm follicle size to enable us to collect the maximum number of mature oocytes.