What is NT/NB scan ?
The nuchal translucency scan is an ultrasound scan and is one part of the Combined First Trimester Screening Test which is offered to all pregnant women. A nuchal translucency scan must be performed during 11weeks –13 weeks 6days (fetal size CRL i.e. length of your baby from head to bottom 45mm- 84mm) of a pregnancy.
The other part is a specific blood test from the mother. All unborn babies have a collection of fluid found under the skin at the back of the baby’s neck. The thickness of this fluid layer is called the ‘nuchal translucency’ and is measured with ultrasound. NB denotes nasal bone.
The ossification i.e. the bony mineralization of nasal bone is assessed. Nuchal translucency is measured because research has shown a link between the thickness of the fluid and an increased risk of common chromosomal abnormalities such as Down Syndrome.
Factors such as the mother’s age, weight, blood test results, and the nuchal translucency details, are combined to give you a result. This is a screening test and will not tell you if your baby definitely has an abnormality but may help decide if further testing is needed
What is to be done prior to examination ?
Kindly take appointment at least one day prior to exam. Please come with a comfortably full bladder. Kindly turn off your phone/keep it in silent mode before entering the ultrasound room and throughout the examination.
What will happen during the examination?
The scan will be performed in dimly lit room and you would be asked to lie on a flat couch. Clear(perhaps cold) ultrasound gel will then be applied and the ultrasound specialist will commence the exam. To get optimum views of your baby, slight pressure may have to be applied.
- The time duration varies, but is usually between 15 -30min.
- If your baby is not in a very easy position for the ultrasound specialist to see, you may be asked to wriggle your hips, jump up and down, walk around outside or come back at another time or date.
- Sometimes due to a number of factors an abdominal scan may not be sufficient and you will be offered a transvaginal scan. This would involve a long thin probe with a cover being inserted into the vagina for a clearer view. This does not hurt and will not harm the baby.
- If when you are scanned, the baby is too small(CRL <45mm), you may have to return on another day for another appointment.
- If when you are scanned, the baby is larger than expected(CRL >84mm), the combined screening may not be possible.
- Ultrasound imaging uses soundwaves to take pictures. It is radiation free and is not harmful to you or your unborn baby.
*Benefits
It can be used as a dating scan if it’s not already done
NT/NB scan alone with maternal age can detect down syndrome(trisomy 21) in around 60% cases.
Combining it with blood test increases the detection rate considerably(Combined first trimester screening).
Additional evaluation of fetus like Ductus venosus(a vessel in fetal abdomen) doppler, Tricuspid regurgitation(evaluated in fetal heart) and Uterine artery(vessel supplying blood to the womb) doppler can be done.
It is possible to rule out some major structural abnormalities of fetus in this scan.
Uterine artery dopplers alone or in combination of blood tests can be used to calculate risk of you having pre-ecclampsia (a condition in which blood pressure increases during pregnancy with/without protein in urine) in the current pregnancy
*Scan at Fetal Experts Lucknow is done in accordance with international guidelines(ISUOG, FMF).
Limitations
Ultrasound alone cannot exclude all structural defects, chromosomal abnormalities and rare genetic disorders.
This is a screening test and will not tell you if your baby definitely has an abnormality but may help decide if further testing is needed. A low risk result is highly reassuring but it does not denote zero risk.
What happens after the examination?
You would usually receive the printed report on the same day. You can take appointment for any subsequent scans which would then be arranged at the correct time.