Extracted from Myles Textbook for Midwives 15th Edition. Diane M. Fraser, Margaret A. Cooper (Eds). London; Churchill Livingstone: 2009. Courtesy Elsevier.

The measurement of nuchal translucency (NT) at 10 - 14 weeks' gestation can provide information about the developing fetus. Increased NT is associated with chromosomal abnormalities, structural and genetic disorders. This information can be used in combination with maternal age and biochemical markers to assess the risk of Down syndrome. In general, mothers appreciate the opportunity for early information so that they can consider the option of termination before they are visibly pregnant and can feel the baby's movements. However, this can also be a disadvantage in that parents are faced with a decision about whether to terminate a pregnancy that may be destined to miscarry naturally. Approximately 40 per cent of affected fetuses die between 12 weeks' gestation and term.

Nuchal fold measurement

Nuchal fold >5mm at 20 weeks' gestation is a marker of chromosomal abnormality. After 14 weeks' gestation, nuchal translucency can no longer be visualised and the nuchal fold is measured instead. A thick nuchal fold is often considered to be the most sensitive and most specific second trimester marker for Down syndrome.