Ovarian hyperstimulation (also called controlled ovarian hyperstimulation) is where a regimen of fertility medications are used to stimulate the development of multiple follicles of the ovaries in one single cycle, resulting in superovulation (release of a larger-than-normal number of eggs). It may be used as a part of in vitro fertilization. Treatment cycles are typically started on the third day of menstruation.
Medications used 
In most patients injectable gonadotropins are used, usually FSH analogues. A meta-analysis came to the result that the optimal daily recombinant FSH stimulation dose is 150 IU/day in presumed normal responders younger than 39 years undergoing IVF. Compared with higher doses, this dose is associated with a slightly lower oocyte yield, but similar pregnancy rates and embryo cryopreservation rates. There is a concomitant monitoring, including frequently checking the estradiol level and, by means of gynecologic ultrasonography, follicular growth. Typically approximately 10 days of injections will be necessary. Concomitantly administering recombinant hCG has no significant beneficial effect. Spontaneous ovulation during the cycle is typically prevented by the use of GnRH agonists or GnRH receptor antagonists, which block the natural surge of luteinising hormone (LH).
Tracking or supervising the maturation of follicles is performed in order to timely schedule oocyte retrieval. Two-dimensional ultrasound is conventionally used. Automated follicle tracking does not appear to improve the clinical outcome of assisted reproduction treatment.
When used in conjunction with in vitro fertilization (IVF), ovarian hyperstimulation may be followed by ovulation induction using human chorionic gonadotropin (hCG). hCG makes the follicles perform their final maturation. A transvaginal oocyte retrieval is then performed just prior to when the follicles would rupture. Alternatively, coasting may be performed, which is ovarian hyperstimulation in IVF without hCG administration. Coasting radically decreases the risk of ovarian hyperstimulation syndrome (OHSS), with a study of high risk patients showing no incidence of OHSS in 21 patients, versus ~20% in the control group. On the other hand, live birth rate may be slightly decreased, with the same study resulting in 38% in coasting vs. 45% among controls, as well as decreased cumulative live birth rate (52% vs. 59%), presumably because of more difficulty in timing oocyte retrieval with full maturation. However, there appears to be no significantly decreased birth rate among high responder patients, in the associated study defined as those having at least 20 follicles, each measuring ≥10 mm in diameter with ≥20% of them of diameter ≥15 mm.
Response predictors 
Antral follicle count 
The response to gonadotropins may be roughly approximated by antral follicle count (AFC), estimated by vaginal ultrasound, which in turn reflects how many primordial follicles there are in reserve in the ovary.
In regard to how many antral follicles are achieved in "response" to ovarian hyperstimulation, women may be designated as low (or poor) responders, normal or average responders or high responders.
|Antral follicle count||Classification||Approximate expected response||Risks||Pregnancy rates||Recommendation|
|Less than 4||Extremely low||Very poor or none||Cancelled cycle expected||0–7% with 1 oocyte||Not attempt IVF|
|4-7||Low||Possibly/probably poor response||Higher than average rate of IVF cycle cancellation||15%||High doses of gonadotropin likely|
|8-10||Reduced||Lower than average||Higher than average rate of IVF cycle cancellation||Slightly reduced|
|11-14||Normal (but intermediate)||Sometimes low, but usually adequate||Slight increased risk for IVF cycle cancellation||Slightly reduced compared to the "best" group|
|15-30||Normal (good)||Excellent||Very low risk for IVF cycle cancellation. Some risk for ovarian overstimulation||Best overall as a group
with approx. 35%
|Low doses of gonadotropins|
|More than 30||High||Likely high||Overstimulation and ovarian hyperstimulation syndrome||Very good overall as a group,
but potential egg quality issues
|Low doses of gonadotropins|
Older poor responders have a lower range of pregnancy rates compared with younger ones (1.5–12.7 versus 13.0–35%, respectively).
- Elevated basal Follicle stimulating hormone (FSH) levels imply a need of more ampoules of gonadotropins for stimulation, and have a higher cancellation rate because of poor response.
- Circulating Anti-Müllerian hormone (AMH) can predict excessive and poor response to ovarian stimulation. For predicting an excessive response, AMH has a sensitivity and specificity of 82% and 76%, respectively. Overall it may be superior to AFC and basal FSH.
- Advanced maternal age causes decreased success rates in ovarian hyperstimulation. In ovarian hyperstimulation combined with IUI, women aged 38–39 years appear to have reasonable success during the first two cycles, with an overall live birth rate of 6.1% per cycle. However, for women aged ≥40 years, the overall live birth rate is 2.0% per cycle, and there appears to be no benefit after a single cycle of COH/IUI. It is therefore recommended to consider in vitro fertilization after one failed COH/IUI cycle for women aged ≥40 years.
Ovarian hyperstimulation does not seem to be associated with an elevated risk of cervical cancer, nor with ovarian cancer or endometrial cancer when neutralizing the confounder of infertility itself.
In vitro maturation is letting ovarian follicles mature in vitro, and with this technique ovarian hyperstimulation isn't essential. Rather, oocytes can mature outside the body prior to IVF. Hence, no (or at least a lower dose of) gonadotropins have to be injected in the body. However, there still isn't enough evidence to prove the effectiveness and security of the technique.
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