When should one go for a baby scan?

Evidence on the internet states that there may not be any defined date for scans carried out during pregnancy other than the first scan that would be done at around 6 to 10 week period. An article states that the National Health Service has cut back in some areas and only offering one scan during the 6 to 10 week period and no other scans if a pregnancy appears to be a healthy pregnancy. The majority of health authorities do still carry out the 6 month scan and when that scan occurs parents may be offered the sex of the baby as well as pictures of the unborn child. An article states that a text book answer to when a scan would take place would be different and dependent on the health authority and the risk factor to mother and baby.