Nuchal Scan

pregnancy scan 3d 4d

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

The vast majority of babies are healthy, but about 1 in 100 are born with a serious mental or physical handicap. One of the commoner conditions is Down’s syndrome, when the baby receives an extra chromosome 21 (Trisomy 21). It is more common with older mothers, but can occur whatever the age of the mother. Today, with the tremendous advancement in the ultrasound technology, the fetus can be seen clearly by ultrasound examination which is carried out through the abdomen in most instances. 

The nuchal scan is an ultrasound scan performed between 11 and 13+6 weeks of pregnancy, during which the fluid at the back of the baby's neck (the nuchal translucency) is measured. All babies will have some fluid here, but in the majority of babies with Down’s syndrome the fluid tends to be increased.

First trimester serum biochemistry: A blood test taken from the mother can be used to measure the levels of two hormones (free ß-hCG and PAPP-A). In about 60% of the pregnancies affected by Down’s syndrome there is a tendency for the levels of free ß-hCG to be increased and PAPP-A to be decreased

The nuchal scan is done to assess the risks of Down’s Syndrome and other chromosomal abnormalities. Each woman will be given an estimate of her individual risk for this pregnancy. At The Avenue Clinic this is calculated by taking into account:

* Screening by maternal age alone picks up about 30% of the babies with Down’s syndrome.

* Screening by nuchal translucency picks up about 80% of the babies with Down’s syndrome. Screening by free ß-hCG and PAPP-A alone picks up about 60% of the babies with Down’s syndrome.

* The combination of these three methods, picks up about 90% of the babies with Down’s syndrome.

* Combining the nuchal translucency with the nasal bone or the tricuspid flow or the ductus venosus picks up about 93 - 95% of the babies with Down's syndrome.

After the scan, on the basis of all the above factors, the estimated risk for Down’s syndrome will be calculated and the parents will receive full counselling concerning the significance of this risk and the various options for further testing. Irrespective of whether or not you decide to have an invasive test, it is recommended that you have a scan at 20 weeks to check for physical abnormalities

The nuchal scan is also used in the following:

Diagnose multiple pregnancy

Approximately 2% of natural conceptions and 10% of assisted conceptions result in multiple pregnancy. Ultrasound scanning can identify if twin babies are sharing the same placenta which can lead to problems in the pregnancy. In such cases it would be advisable to monitor the pregnancy more closely.

Diagnose certain major fetal abnormalities

Major abnormalities may be visible at the nuchal scan but a 20 week anomaly scan is still essential.

Diagnose early pregnancy failure

Unfortunately, in about 3% of women who attend for a nuchal scan it is found that the fetus has died, often several weeks before and without any warning. Couples will receive full counselling as to the possible causes of this problem and the options for subsequent measures that may be necessary.