Controlled Ovarian Hyperstimulation (COH)

Definition - What does Controlled Ovarian Hyperstimulation (COH) mean?

Controlled ovarian stimulation (COS) is a technique used in assisted reproduction that consists of using fertility medications to grow multiple fluid-filled sacs inside the ovaries called follicles, which then develop numerous mature eggs. The goal of carrying out COS is to obtain as many mature eggs as possible since not every egg will have the potential to be fertilized and subsequently give rise to an embryo that is genetically normal.

FertilitySmarts explains Controlled Ovarian Hyperstimulation (COH)

COH comprises three basic stages:

  • Giving hormonal medications called gonadotropins like follicle-stimulating hormone (FSH) to stimulate the growth of ovarian follicles which then develop and mature the eggs
  • Giving medications to prevent premature surges in luteinizing hormone (a gonadotrophin which triggers the release of eggs from follicles) and thus prevent premature ovulation, allowing more time for the eggs to develop
  • Giving human chorionic gonadotrophin (hCG) shot to trigger final egg maturation that takes place after 36 to 38 hours, following which the eggs can be retrieved.

The COH protocols are not the same for all women. Instead, they are customized based on a woman’s predicted ovarian response. Factors like age, past history, hormonal levels (FSH, LH, estradiol, antimullerian hormone/AMH), and antral follicle count (AFC) serve as the ovarian reserve markers or markers of the number of eggs available.

As per the predicted ovarian response, women fall into three categories:

  • Intermediate responders: These women show a normal ovarian reserve as indicated by a normal LH/FSH ratio, normal AMH levels and a normal ovarian volume with an adequate number of antral follicles.
  • High responders: These women have a high ovarian reserve, polycystic ovarian syndrome-like features with either a high LH/FSH ratio or multiple follicles within the ovaries. In response to ovarian stimulation, high responders are likely to produce a surplus of follicles and are at risk of ovarian hyperstimulation syndrome (OHSS).
  • Poor responders: Typically these are women with advanced age and low ovarian reserve (as indicated by high day 3 FSH levels, low AMH levels, and/or a low ovarian volume). Their chances of egg retrieval and therefore successful pregnancy are poor.

Determining a woman’s ovarian response as high, intermediate, or low is critical to optimize COH protocols as well as to reduce the risk of complications such as cycle cancelation owing to insufficient response or, on the contrary, the risk of OHSS.

In high responders, a gentler stimulation protocol is thus used, and the dose of hormones adjusted in an individualized fashion using a step-down protocol while monitoring the estrogen levels and follicular development and growth by transvaginal ultrasound. These women typically receive a hormonal protocol of short duration and gonadotropin analog instead of the hCG trigger shot for final egg maturation to avoid the risk of OHSS. Conversely, poor responders receive higher doses of hormones than the intermediate or high responders.

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