First trimester screening by N T Scan & serum Double markers

 

Point 1: Nuchal translucency and  nuchal thickness ate not alike. N 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.

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.

Point 2:--If NT is raised what are the possibilities that lurk in the minds of HCP(Health Care Providers) ? What may be associations with increased NT > 3 mm??

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,  & 4) non-aneuploidy structural defects and syndromes, 5) congenital diaphragmatic herniation, 6) congenital heart disease, 7) omphalocoele , 8) skeletal dysplasias.

9) Smith-Lemli-Opitz syndrome and lastly

10) VACTERL association

Point 3: Nuchal lucency is measured Technique

??  Nuchal lucency is measured on a sagittal image through the fetal neck. Technique must be  correct & that is essential: The fetus must be in mid sagittal imaging plane (the vertebral column should be facing the bottom of the screen);

Point 4: How do I know that  I am in correct midsagittal plane??? The  following structures must be seen to confirm correct mid sagittal position:

1)two tiny parallel echogenic lines 

2)tip of the nose

3)nasal bone (if not absent)

4)hard palate 

5)diencephalon 

Tips 2:

:-How much to magnify the image?? Ans. The magnification so that only fetal head and upper thorax included in the image: enabling 1 mm changes in measurement possible

Tips 3:Fetal head should not be extended or flexed 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

 Tips 4:

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

Tips 5: At what period of gestation this NT has to be assessed ?  What to assess??

Ans: Values 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 it  is the  thickness rather than the appearance (morphology) is considered to be directly related to the incidence of chromosomal and other anomalies.

Point 4: 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)

Nuchal translucency cannot be adequately assessed if there is: A) unfavourable fetal lie

B) unfavourable gestational age: C) CRL <45 or >84 mm,

Interpretation : The rate of aneuploidy is almost nil when the nuchal translucency is <2 mm or say less than  1%.,

Point 5: How important is Double marker (serum markers)  and its correlation with Observed NT and her age??  As: To increase the clinical accuracy of nuchal lucency, NT  can be correlated with serum markers such as:

A)maternal free  B-HCG,  B)  pregnancy-associated plasma protein A (PAPP-A) and occasionally oestriol/estriol  

Point 6: Can we avoid D marker tests and rely only on NT –Is NT alone helpful?? Ans : No .  D marker is useful ?? The combination of nuchal translucency thickness, PAPP-A, and 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 

Point 7: Suppose risk is < 1:300. Then ???   What will be the further work up

If abnormal and screening test results show increased risk of: less than 1 in 300??  

Ans: Further work-up may carried out based on patient's desire after counseling and which includes:   chorionic villus sampling amniocentesis and/or  fetal echocardiography,

 

Point  8: Prognostication: Ebb & tide of NT !!! Treatment and prognosis

As the second trimester approaches, the region of nuchal translucency might either  regress

if chromosomally normal, a large proportion of fetuses will have a normal outcome

spontaneous regression does not however mean a normal karyotype

evolve into nuchal oedema,cystic hygroma

 Point  9 :  Do it yourself initially but if doubtful about NT in the following circumstances pl do refer to Foetal Medicine specialist .Such aberrations of  NT can happen by novish sonologist like us   e.g.

1)incorrect technique,  2) fetal neck skin thickening due to first-trimester hydrops fetalis 3) amniotic membrane lying behind fetal neck, 4) chorio-amniotic separation.