Inaccurate dating of the pregnancy
Ultrasound scans are considered to be safe for you and your baby when performed by trained professionals.
However, sometimes, having a scan can cause unnecessary worry.
If you prefer, you can have a private screening test.
As well as the combined test, most private healthcare clinics offer non-invasive prenatal testing (NIPT), which is the most accurate (up to 99 per cent) screening test for Down's Syndrome.
Therefore, from 13 weeks, or if your baby is longer than 84mm, the circumference of the head becomes the best way to measure your baby. Evaluation of gestation emedicine.[Accessed July 2017] Newson L. The scan will usually show that your pregnancy is less far along than suggested by your LMP. This means that accurate dating reduces your chance of having your labour induced because your baby is thought to be overdue. For example, the NT scan for Down's syndrome has a false-positive rate of five per cent. This means that, out of 20 women who have the scan, one woman will be wrongly told she has a high chance of having a baby with Down's syndrome.
It's entirely up to you whether or not you have a scan.