Chromosome marker scans are performed in the middle part of pregnancy. You will probably have heard of this scan:

• from your screening midwife at an NHS hospital if you have had a high risk result from a triple test
• if you were more than 14 weeks when deciding to have Nuchal Translucency screening for Down's Syndrome

In the middle part of pregnancy minor differences may be seen using ultrasound scanning. These differences are termed ‘ markers’ for chromosome abnormalities and some babies may have an increased chance of having a chromosome abnormality.

Such markers include:

• Choroid plexus cysts (cysts in the part of the brain which produces spinal fluid)
• A nuchal fold of greater than 5mm (this is increased skin swelling at the nape of the baby's neck)
• An echogenic focus within the baby's heart (white echoes in the heart chambers)
• Echogenic bowel (bright appearance of bowel, possible link with cystic fibrosis and viral infections)
• Short thigh bone (femur)
• Although not an ultrasound finding, maternal age over 37 is considered a marker
• Similarly being screen positive (nuchal scanning or from serum screening) is also considered to be a marker. We will obtain the results from serum screening (NHS triple test) and combine with our ultrasound scan

These ultrasound "differences" will disappear with time and are not structural abnormalities. On their own they are not significant but two or more ‘markers’ increase the risk of a baby having a chromosome abnormality.

Not all chromosome abnormalities can be screened for and the scan looks for specifically Down’s, Edward’s and Patau’s Syndromes and is a detailed examination of all of the baby.

It is important to remember that most scans are normal.

Following the ultrasound scan your consultant will discuss what they have seen on the ultrasound and give you your individual risk of having a baby with one of these chromosome abnormalities. High risk is classified where there is a risk greater than 1 in 250 that the baby may have a chromosome abnormality. Your individual risk is discussed in depth with you and if there is the need for further tests or examinations this will be explained so that you know the options available to you and you can make informed choices about what if anything to do next.

You will receive a CD and black and white (thermal) pictures of your baby together a medical written report. We will also ask if you would like a copy of the report sent to your GP and the screening midwife at NHS hospital whose care you are under.