Having a sufficient number of mature egg cells is one of the key steps to obtaining excellent results in a cycle of in vitro fertilisation (IVF). In order to achieve this, the ovaries need to be stimulated and, contrary to what happens during a natural cycle, the ovaries need to simultaneously mature an appropriate number of eggs.

The most commonly used stimulation protocols are based on the use of doses of follicle-stimulating hormone (FSH). These may or may not be administered along with other drugs and vary between 150 and 300 IU/day. The response will be somewhere between 7 and 15 follicles.

When comparing elevated doses with lower doses, numerous clinical trials do not show that results improve when aggressive stimulation protocols are applied.

The medication used in ovarian stimulation processes of this kind are expensive, they need to be injected on a daily basis and they generally need to be taken for between 8 and 14 days. Furthermore, regimens of this kind are not entirely free of side effects such as ovarian hyperstimulation syndrome (OHSS). It is also possible that supraphysiological levels of oestradiol generated as a result of stimulation of this kind may have a potentially negative impact on endometrial receptivity, oocyte quality and, therefore, on embryo quality.

The use of a less aggressive stimulation procedure, known as soft IVF or mild stimulation, could be an alternative to conventional protocols. The aim is to simplify stimulation and make it more convenient, reduce the cost and the side effects, as well as reduce and even replace the number of injections, even if the resulting number of oocytes is slightly lower.

The problem we may face when putting soft IVF into practice is that a reduced ovarian response could reduce pregnancy rates. However, improved laboratory efficiency and the current tendency to limit the number of embryos being transferred means that a large quantity of oocytes are not so necessary. Stimulation of this kind would, nevertheless, only be recommendable for patients with normal ovarian reserve levels, patients who are not of advanced age and who are not at risk of OHSS, as is the case of patients with polycystic ovary syndrome.

Dr Rafael Bernabeu, Medical Director at Instituto Bernabeu.

and Dr Belén Moliner, gynaecologist at Instituto Bernabeu.

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