In theory you can get pregnant straight away after removing an iud, some women even become extra fertile for a while, that's why doctors will usually advise you to use condoms if you are changing to a different method of birth-control. Usually though you will have to wait for your cycle to become regular again, especially if you didn't have periods at all when using the iud. This could take anything from a month to a year or maybe more. Your GP should be able to give you more advice.