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Prevention of ovarian hyperstimulation

One of the major complications that plague ovulation induction and controlled ovarian hyperstimulation (COH) is ovarian hyperstimulation syndrome (OHSS). OHSS can be so serious that it may even be life threatening. It is, however, very largely preventable and awareness of the possibilities that it may occur is the first step in prevention. OHSS is brought about by overstimulating the ovaries with gonadotrophins, whether during ovulation induction or COH before intra-uterine insemination (IUI) or IVF. Knowing the risk factors predisposing to OHSS is an essential ingredient in the prevention of the syndrome. Those at particular risk to develop OHSS are young, lean and/or have polycystic ovaries or have had OHSS in a previous cycle. For these, the use of smaller starting doses than routine and small incremental dose rises are called for. A suspicion of impending OHSS can also be made during gonadotrophin stimulation. In ovulation induction and stimulation before IUI, the development of more than 5-6 follicles >9mm diameter or in IVF, >30 such follicles should set the alarm bells ringing and urge a consideration of some preventive action as should very high levels of oestradiol. These are pointers which urge awareness and watchfulness.

Human chorionic gonadotrophin (hCG) is routinely used as the trigger for ovulation following stimulation with gonadotrophins. OHSS does not occur if hCG is not given.

If the danger of OHSS looks imminent during ovarian stimulation, withholding hCG and abandoning the cycle is the surest way to prevent OHSS. It is better to ‘lose’ a cycle than take the risk of putting the patient (and doctor) through the agonies of severe OHSS. Giving one shot of a GnRH agonist as the trigger instead of hCG will prevent OHSS in IVF cycles in which a GnRH antagonist is being used but strong support of the luteal phase is needed to maintain good results. Embryo freezing is a viable method to prevent OHSS following the use of a GnRH agonist trigger in a cycle destined for OHSS. Embryos obtained are frozen and, rather than being replaced in the same cycle, are later thawed and replaced in a non-stimulated cycle.

If overstimulation occurs during ovulation induction, some would advocate recourse to IVF in order to prevent OHSS without abandoning the cycle, so-called rescue IVF. The problem of this approach is that a snap decision has to be taken by both patient and doctor without the usual preparation, both emotional and physical, for an IVF procedure.

In-vitro maturation of oocytes (IVM) could provide a satisfactory reduction in OHSS rates for particularly susceptible patients. IVM performed in most centres is not, however, presently producing acceptable results.

Anil Gudi, Amit Shah &Prof Homburg

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