Screening tests are used to assess the chance of your baby having a chromosomal or structural condition. If a screening test suggests an increased chance of a particular condition, a diagnostic test is performed to find out if the condition is actually present. Around 2% of all babies are born with some kind of abnormality. Most are minor, such as fused toes or skin tags. However, a very few babies will have more major problems, such as heart defects, spina bifida and chromosomal irregularities. In most cases, screening tests provide reassurance that everything is OK. The National Screening Unit oversees pregnancy and newborn screening in New Zealand.