HCG injections are nearly always used when FSH is used. FSH stimulates the egg-maturing process and the development of the follicles on the ovaries, and is given each day from day 2 or 3 of the cycle. When the oestrogen level reaches its peak, an ultrasound will be done and the HCG injection will be given as appropriate. When using FSH it is very important to monitor its effect by regular blood and ultrasound tests as this treatment is more likely to cause a multiple pregnancy. At Fertility North FSH is given as either Gonal-F or Puregon and HCG as Pregnyl or Ovidrel. What are the risks involved? When using these induction agents, there is a slightly increased chance of producing too many follicles, or indeed producing so many as to call this hyperstimulation (OHSS- discussed elsewhere). Ideally one to two follicles are expected. If there are more than one or two, the cycle is very likely to be cancelled, and your specialist for ongoing treatment will reassess you.