Occasionally, the position of the baby makes visualising the back of their neck very difficult. If this is the case, the ultrasonographer may ask you if they can perform the ultrasound vaginally (called 'transvaginal'). This means the ultrasound probe is covered by a plastic sheath, similar to a condom and gently placed inside the vagina (but outside the cervix). The 'transvaginal' ultrasound enables the ultrasonographer to look more closely at the baby.
NOTE:Most women do not expect that their nuchal translucency could involve placing something into their vagina. A few women will feel very strongly about not having their nuchal translucency done in this manner. Be aware that you are not obliged to consent to it if you do not feel comfortable about having a transvaginal ultrasound. You may opt to have the abdominal ultrasound repeated a few days later, or decline to continue with the test all together.
What will a NT tell me?
Generally, the larger the measurement (or depth of fluid), the greater the chance the baby may have a genetic disorder. However, there is no 'normal' measurement because it varies widely between babies, and can even vary for different pregnancies in the same woman. The measurements are also interpreted in relation to each woman's age. As a guide, the 'top' level of normal tends to be somewhere between 2 to 3 millimetres (mm), with above 3mm definitely being larger than normal.