Ovulation Induction versus Controlled Ovarian Hyperstimulation

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Ovulation Induction versus Controlled Ovarian Hyperstimulation

Ben J. Cohlen


Chronic anovulation is a common feature in infertile couples. It is unknown how many couples suffer from anovulation in the general population, but estimates vary between 5% and 15%. Being a sign rather than a disease, chronic anovulation is treated in various ways, depending on the underlying cause.

Although with ovulation induction, treatment is started to regain monthly mono-ovulation, the aim of treatment in controlled ovarian hyperstimulation is the development and ovulation of at least two dominant follicles to improve pregnancy chances in an ovulatory patient. However, two very different treatment strategies, ovulation induction (OI) and controlled ovarian hyperstimulation (COH), are often mixed up, which might result in unnecessary complications (Chapters 23 through 26).

In this chapter, both treatment modalities are defined and discussed.


The WHO-ICMART committees defined ovulation induction as follows: pharmacologic treatment of women with anovulation or oligo-ovulation with the intention of inducing normal ovulatory cycles (1). From this definition, we can conclude that the intention of OI is the release of one oocyte per cycle, resembling normal ovulatory cycles. Thus, the goal of OI should be monthly mono-follicular development and mono-ovulation.

Controlled ovarian hyperstimulation in NON-ART cycles (the WHO calls it controlled ovarian stimulation) is defined by the WHO-ICMART as pharmacologic treatment for women in which the ovaries are stimulated to ovulate more than one oocyte. Thus, the goal of COH in NON-ART should be (monthly) multi-follicular development and multiple ovulations. In this definition, NON-ART stands for hyper-stimulated cycles besides IVF or ICSI.

Existing Evidence in COH for NON-ART

Why should we stress this difference in approach between COH and OI? Regaining normal ovulatory cycles in women with anovulation, patent tubes, and a partner with normal sperm parameters restores almost normal fertility. Cumulative live birth rates of up to 70% in two years in anovulatory women have been reported (2), almost resembling normal fertility rates. Furthermore, a successful outcome in fertility treatment is defined as the live birth of a healthy singleton. Mono-ovulation is a requirement to achieve this goal.

In COH cycles, the goal is the same: the live birth of a healthy singleton. However, one tries to enhance fertility by releasing two to three oocytes in couples with often a period of unsuccessful mono-ovulation combined with intercourse (unexplained or mild male subfertility, minimal to mild endometriosis) (3) (LOE 1a). Multi-follicular development is one of the keystones for success. It is even questionable whether mono-follicular development in COH cycles increases pregnancy rates. With this strategy, however, one incorporates the chance of achieving a multiple pregnancy, and couples should be informed about these chances beforehand.

Treatment of anovulation with ovulation induction is the subject of Chapters 14 through 21 and will not further be discussed in this chapter.

When to Start COH?

It is obvious that COH is applied in IVF or ICSI cycles. In couples with mild male or unexplained subfertility, it is hypothesized that the subfertility of the couple is related to the subfertility of the woman, and COH in combination with IUI is the most cost-effective first-line treatment option when spontaneous changes are low (4

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