"Most babies are born healthy, but when a baby features a condition that's present from birth, it's called a birth defect. Congenital disorders are often inherited or caused by environmental factors and their impact on a child’s health and development can vary from mild to severe. A child with a birth defect may experience a disability or health problems throughout life. Testing for congenital disorders are often performed from 10 weeks of pregnancy onwards. While many parents prefer to have tests during pregnancy, it's not compulsory and a few don't. Screening tests are designed to spot babies who don't have a birth defect. If a screening test doesn't rule out your baby having a birth defect, the subsequent step is to possess a diagnostic assay. Diagnostic tests, like ultrasound scans, blood tests, and sometimes urine tests, are designed to spot babies who do have a birth defect, and to seek out out what that disorder is. However, it's impossible to check for all congenital disorders during pregnancy, and testing isn't perfect.