This means that combined first trimester screening simply tells us if your risk is low or high.

Combined first trimester screening assesses the risk for your baby having certain chromosomal abnormalities (trisomy 13, 18 and 21).

This testing combines the nuchal translucency ultrasound with specific blood tests.

We know that the amount of fluid can increase in the presence of certain conditions, producing a thicker NT measurement.

Conditions associated with an increased NT measurement include some chromosome abnormalities (for example, trisomy 13, 18 and 21) and some structural problems (for example, heart abnormalities).

It is important for the measurement to be done properly to ensure an accurate result.

If your baby is not co-operating and the NT cannot be measured accurately, we may ask you to return for more images later in the day.The probe is then gently inserted a short distance into the vagina by the sonographer.All transvaginal probes have been cleaned and sterilised according to recommended protocols.An increased NT measurement does not always mean the baby has a problem but it does increase the risk.There are established and strict criteria for the accurate measurement of the nuchal translucency.Chorionic villus sampling and amniocentesis are invasive tests, involving putting needles into the placenta or amniotic sac, and they are associated with an increased risk of miscarriage.