Prenatal screening cannot be repeated. This is because, as mentioned earlier, the results tell you your risk of having a fetal abnormality based on a comparison with most people of the same gestational age, and are not a definitive fetal diagnosis. There is no point in repeating the screening test; it is not like other diagnostic tests that tell you if there is a problem and can be repeated to confirm the results. And if two tests give opposite results, you are even less likely to make the right choice. So if screening is high risk, it is important to calculate and check again the week of gestation, weight, age and various elements in your medical history, not to redo the test.