The success rate, sometimes narrowly measured as 'take-home baby' rate, will vary between 5 - 50% per attempt, depending upon the women's age , the number of eggs retrieved, the number that are fertilised (dependent also upon the sperm), the number of embryos transferred and the state of the uterus. To keep all this in perspective it is important to realise that the 'natural' pregnancy rate in our society is, at best, only between 15 - 20 % per month – many people find that surprising.