The Nuchal Scan (11 weeks - 13 weeks, 6 days)

Pregnancy Ultrasound

The majority of babies are born normal. However all women have a risk of carrying a baby with a physical or mental handicap. One cause of this may be a chromosomal abnormality, such as Down's syndrome.

The risk of having a baby with such an abnormality can be calculated on the basis of maternal age, the amount of fluid behind the baby's neck, the length of the baby and 2 hormones in your blood. Your and your partner can then decide if the risk of the baby having Down's syndrome is acceptable or if you would like to have an invasive test such as a CVS or amniocentesis. These two tests carry a miscarriage rate of 1 %.

The scan is performed between 11 weeks and 13 weeks and 6 days. An ultrasound transducer is placed on your abdomen and the procedure takes around 20 minutes. You should drink normally before the arriving but do not empty your bladder 30 minutes before the scan.

During the scan, several measurements are taken

• The crown rump length (CRL) from the top of baby's head the bottom
  of the spine
• This will enable us to accurately calculate how pregnant you are and the estimated date of delivery
• The fetal heart rate
• The nuchal translucency measurement (NT). This is the fluid filled space behind the neck that is present in all fetuses.

The fetal anatomy will also be examined, as there are some physical abnormalities that can be diagnosed at this stage of pregnancy. We will examine the skull and brain, the nasal bone the arms, the legs, the stomach, the spine, the abdomen and the bladder.

The accuracy of this test is increased by measuring the level of two hormones in the mother's blood (Beta HCG & Papp-A)

Results
After the scan you will be fully counselled about the results and the role of any invasive tests that may be offered. The only way to know for certain if a chromosomal abnormality affects the baby is to have a CVS or amniocentesis.