Ultrasound dating accuracy early
However, conception doesn't actually occur until around 14 days after your LMP, or later if your cycle is longer than 28 days. Multiple pregnancy: antenatal care for twin and triplet pregnancies CG129. You may know when your LMP was, but not when you actually conceived.
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. 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. It shouldn't be uncomfortable, and you don't need a full bladder Your sonographer will give you a report of the scan, which will tell you exactly how many weeks pregnant you are.
Keep it with your maternity notes so your midwife and anyone else involved in your care can see it. This measurement, known as the crown rump length (CRL), is very accurate in the first trimester.
It may also help you to avoid feeling disappointed towards the end of your pregnancy if you think your baby is late when he's not.
The scan can check that your baby's heart is beating nicely and that he's developing normally.
That will happen at your next routine scan at about 20 weeks However, some major problems can be seen at your dating scan, such as issues with the umbilical cord or with your baby's skull or abdominal wall.
You may need a second scan to check the first scan's findings.
It won't hurt, although you may feel a little pressure on your tummy.