Dating scan

The dating and/or nuchal translucency scan is the first routine scan.

This first routine scan is carried out for the following reasons:

  • to confirm when the baby is due:
    the early scan helps us to work out the date when your baby is due. We might suggest a different date from that indicated by your last period. This is because not all pregnancies are conceived exactly 14 days after the first day of the last period. If your pregnancy is the result of assisted conception, we would normally calculate the delivery date from the date of your treatment. It is important to know your final due date for your care later in pregnancy.
  • to see if you are expecting more than one baby:
    most families would like to know if twins are expected to help them to plan ahead. It is also important to help us to plan your care appropriately. If we find that you are expecting twins, this is the best time to determine whether this is a dichorionic (non-identical) or monochorionic (identical) twin pregnancy.
  • to confirm the baby’s heart is beating
  • to detect problems of development that can sometimes be seen at this early stage
  • to detect other problems such as ovarian cysts (in you, not your baby)
  • to perform combined screening for Down’s syndrome if this is what you wish

Since November 2010, the Rosie hospital has offered all women screening for Down’s syndrome at their first routine scan. This is known as ‘combined screening’ because it involves an ultrasound scan (the ‘nuchal translucency scan’) and a blood test. The optimum time for the nuchal translucency scan to be performed is around 12 weeks but it can only be performed between 11 weeks and 2 days and 14 weeks and 1 day.

As with all tests in pregnancy, combined screening for Down’s syndrome is optional. It is not diagnostic. This means that the screening will only identify a baby as being at a ‘high’ or ‘low risk’ of being affected by Down’s syndrome. The screening will not definitely determine whether a baby does or does not have Down’s syndrome. Women who are identified as ‘high risk’ will be contacted directly and offered further testing.

If you do not wish to have combined screening for Down’s syndrome, you will be offered a dating scan. We also like to arrange this for around 12 weeks, but it can be performed between 10 and 14 weeks.

Sometimes, it is not possible to take measurements of the nuchal translucency. In this case, you will be offered the quadruple test (a blood test which can be performed between 14 weeks and 20 weeks + 6 days) as your screening test for Down’s syndrome.

Occasionally during the scan, a miscarriage might be diagnosed even though you might still 'feel pregnant'. In this case, the sonographer (the person who does the scan) will discuss the scan findings with you and arrange for a doctor to see you.

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