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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.
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.
How big your baby will be depends on when you have the scan: After 13 weeks, your baby can curl up and stretch out, so measuring the length becomes less accurate.
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.
If you do know the conception date, this is counted as day 14, not day one.
If your cycle is irregular or you've recently been on the pill, working out the date from your LMP probably won't work. If the scan date differs from your period dates, the scan date will be used.