First Trimester Screening (Nuchal)

The vast majority of babies are born normal, however all women have a small risk of delivering a baby with a physical or mental handicap. One cause of this is a chromosome abnormality such as Down's syndrome. One of the most sensitive tests for assessing the risk is the combined test of nuchal translucency and serum biochemistry. This test is performed between wk 11 and wk 13 + 6 days. It normally involves an abdominal scan but occasionally a transvaginal scan is necessary if the baby is lying in a difficult position. We take several measurements of your baby.

•  The crown rump length (CRL) from the top of the babies’ head to the bottom of the spine, this allows accurate dating of the pregnancy.
•  The fetal heart rate
•  The nuchal translucency (NT) this is the fluid space at the back of the neck, which is present in all babies at this stage but is normally increased in babies with Down's syndrome and some other problems.
•  We will also measure the nasal bone and examine as much of the anatomy as possible at this stage of the pregnancy.
•  A further scan to check the anatomy more fully is normally performed at around 20 weeks.

These measurements will be combined with your age to calculate an individual risk for you, we will also perform a blood test to check the level of 2 biochemical markers in your blood, the results of this test take some time to come back and so you will normally be contacted with your full risk assessment in a couple of days following your test. We recommended that the report be discussed with your midwife.

N.B Ultrasound alone cannot exclude all chromosomal abnormalities and rare genetic syndromes. Using the biochemical markers greatly enhances the accuracy of the test. In the event of low PAPP-A we would recommend an additional scan at wk 28 - wk 30 to assess fetal growth.

This procedure is non-invasive and therefore presents no risk to your baby.  The main benefit is that because it is done in early pregnancy you can use the information to make an informed choice as to whether or not you should consider invasive testing such as amniocentesis.  Invasive testing carries a small risk of miscarriage.  If you have a high risk result or you wish to discus your risk in detail we can arrange for you to be counselled by a fetal medicine expert who will be able to advise you on the need for an invasive test such as CVS or amniocentesis which would give you a definitive answer.

We are an accredited site of the Fetal Medicine Foundation (FMF). Our Sonographers are trained and continually assessed by the FMF and we use the FMF software to calculate your risk. Visit the Fetal Medicine Foundation website for more information.

What Next?

Normally at 20 weeks we would perform an anomaly scan, this is a detailed examination of the fetal anatomy to look for any physical abnormalities, we also assess the growth of the fetus and the position of the placenta at this stage. We would also look for any minor variations of normal anatomy, which are found more commonly in babies with chromosomal abnormalities.

Later in the pregnancy we may perform scans to assess the growth and health of your baby, we would take measurements to assess size and the amount of fluid around the baby. We would also look for fetal movements assess the placenta and measure blood flow in the umbilical cord or uterine arteries.