IVF has very few side effects. It is relatively frequent that the patient notices a certain amount of bloatedness during the ovarian stimulation phase, which typically lasts a few days after the puncture of the ovaries. In the vast majority of cases the treatment is not painful. The puncture of the ovaries does not normally hurt, since sedation is applied. On the day itself you might need a painkiller, which you can take without any problems. Ovarian hyperstimulation syndrome, an illness that is characterised by the loss of liquids through the ovaries that have responded in excess to the stimulation, is highly exceptional nowadays. If a certain risk is observed, medication to prevent its occurrence will be applied and the egg cells or embryos that are obtained will be used in another cycle, avoiding this way that this syndrome can occur. Nowadays, the worst side effect is a multiple pregnancy, which occurs in about 20 % of the cycles.