Nuchal translucenecy

Top of Form

Let us refresh our memory on NT & warning sign of some chromosomal or structural defects: Why  Bottom of Form

Nuchal translucency is raised in some cases? What does such increased NT signify??

Nuchal translucency is a finding during a specific period in the late first trimester and early second trimester (11.3-13.6 weeks) and should not be confused with nuchal thickness which is measured in the second trimester.

Q.1: What exactly happens in N translucency & cut off points ??  Ans: Increased nuchal translucency is thought to be related to dilate lymphatic channels and is considered a nonspecific sign of more generalized fetal abnormality. Measurement of the nuchal latency requires careful attention to technique.

If NT is raised what are the possibilities that lurk in the minds of HCP(Health Care Providers) ? Associations with increased NT > 3 mm??

Q. 2: What are the chromosomal and nonchromosoanl abnormalities associated with increased NT?? Ans: Thickening of the nuchal translucency can be associated with a number of anomalies, including:  1) aneuploidy, 2)  trisomies (including Down syndrome),  3) Turner syndrome, and  4) non-aneuploidy structural defects and syndromes, congenital diaphragmatic hernia ion, congenital heart disease, omphalocele ,dysplasias. Smith & VACTERL association

Q. 3 How is NT measured?? Ans: Nuchal lucency is measured on a sagittal image through the fetal neck. Technique

Use of correct technique is essential:

the fetus must be in mid sagittal imaging plane (the vertebral column should be facing the bottom of the screen); following structures must be seen to confirm correct mid sagittal position:

two tiny parallel echogenic lines 

tip of the nose

a)          nasal bone (if not absent)

b)         hard palate 

c)           diencephalon 

magnification so that only fetal head and upper thorax included in the image: enabling 1 mm changes in measurement possible and of importance is fetal head should not be extended or flexed(neutral position)

fetus should be floating free of the uterine wall i.e. amniotic fluid should be seen between its back and the uterus; this is to not mistakenly measure distance to amniotic membrane or uterine wall. Correct technique for NUCHAL TRANSLUCENCY measurement  as a part of “First trimester of pregnancy “What are the common mistakes while one is carrying out USG for NT & fit trimester—Nasal bone, Ductus Venosus??

📌the fetus must be in mid sagittal imaging plane (the vertebral column should be facing the bottom of the screen);

📌 following structures must be seen to confirm correct mid sagittal position:

Two tiny parallel echogenic lines tip of the nose and nasal bone (if not absent)
hard palate 
diencephalon

Magnification so that only fetal head and upper thorax included in the image:
fetal head should not be extended or flexed
fetus should be floating free of the uterine wall
the "+" callipers should be used 
the callipers are put inside the hyperechoic edges
the widest part of the translucency should be measured. 
It should be measured between 11.3-13.6 weeks and
 it should be less than 3 mm

the "+" calipers should be used for measurement only the lucency is measured (again differing from nuchal thickness) the calipers are put inside the hyperechoic edges the widest part of the translucency should be measured

Assessment

Q5. What does a septate   Translucency  means or signifies??  Ans: Values  are  obtained when CRL is between 45-84 mm (11.3- 13.6 weeks) may be used for combined first trimester screening. The lucent region is generally not septated and the thickness rather than the appearance (morphology) is considered to be directly related to the incidence of chromosomal and other anomalies. A  value of less than ~2.2-2.8 mm in thickness is not associated with increased risk, however it is maternal age dependent and needs to be matched to exact gestational age and crown rump length (CRL).

Q.8: When NT carry little significance ?? Ans:- Nuchal translucency cannot be adequately assessed if there is: unfavourable fetal lie, and gestational age is unfavourable I the sense that: CRL <45 or >84 mm,

Q 9> How to interpret the results?? Ans:-The rate of aneuploidy when the nuchal translucency is <2 mm is less than 1%  but plotting or correlation with serum markers and age is a must for risk stratification. . To increase the clinical accuracy of nuchal lucency, it can be correlated with serum markers.

Q. 11, What are the serum markers that are usually performed ? Ans:- Maternal free B-HCG, pregnancy-associated plasma protein A (PAPP-A).

Q.12: What is the detection rate ?? Ans:-The combination of nuchal translucency thickness, PAPP-A, and free hCG detects 87% of cases of trisomy 21 at 11 weeks, 85% at 12 weeks, and 82% at 13 weeks, with a 5% false positive rate 

Q. 12: What is the cutoff point after we perform NT scan & Double marker tests? What should be the further world up??  

The cut off pint is usually when report comes as risk is 1:300 .If abnormal and screening test results show increased risk of: less than 1 in 300, further work-up may carried out based on patient's desire after counseling  and which includes: chorionic villus sampling. Or

amniocentesis and or  fetal echocardiography,

Treatment and prognosis:  As the second trimester approaches, the region of nuchal translucency might either: A) regress if chromosomally normal, a large proportion of fetuses will have a normal outcome inspite of increased NT . Unfortunately spontaneous regression does not however mean a normal karyotype . There can be later development of  nuchal oedema,cystic hygroma

,Differential diagnosis

incorrect technique,  fetal neck skin thickening due to first-trimester hydrops fetalis

amniotic membrane lying behind fetal neck, chorio-amniotic separation

---

Correct technique for NUCHAL TRANSLUCENCY measurement  as a part of “First trimester of pregnancy “What are the common mistakes while one is carrying out USG for NT & fit trimester—Nasal bone, Ductus Venosus??

📌the fetus must be in mid sagittal imaging plane (the vertebral column should be facing the bottom of the screen);