It involves a blood test and measuring the fluid at the back of the babys neck (nuchal translucency) with an ultrasound scan. This is sometimes called a nuchal translucency scan. The nuchal translucency measurement can be taken during the dating scan.

When should you have a dating scan?

Between 8 – 12 weeks of pregnancy is a good time for a dating scan. A 2-D image of a baby at about 8-9 weeks. Small arms are becoming visible, sticking out slightly in the middle of the baby. The wavy line near the bottom of the image measures the heartbeat which in this baby is 188 beats per minute.