Nuchal Translucency part 1:

 

Nuchal translucency

By

 

Prof. Srimanta Kumar Pal, Kolkata

GD-207, Salt Lake City. Kolkata 700 106’

Email : drsrimantapal@gmail.com

 

 

 

Bulk of the disease burden

 

In India, approximately, 2.5% of infants are born with congenital anomalies which accounts for around 8-15% of perinatal deaths and 13-16% of the neonatal mortality. 6% (1 in 200 newborns) of these have chromosomal abnormalities (CA) and constitute a major cause of mental retardation and congenital malformations. 

 

What is NT & why  Bottom of Form

Nuchal translucency is raised in some cases?

It is the thickness at the nape of nape foetal neck .And if raised above the gestational   range diameter then a possibility chromosomal malformation and or major cardiac or skeletal abnormalities may exist but has to be confirmed by invasive testing like CVS or amniocentesis.

 

When to measure Nuchal translucency at the back of neck of foetus?

 -The optimum time?? 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.

 

Drugs --At what  in early week Will cause Cong abnormalities ??

 

Most drugs are teratogenic between 8-11 weeks (embryogenesis) while at other times the drug (category c) is feto-toxic that is cause miscarriage being anti esṭrogenic.

 

 

 

What period of gestation

The NT should ideally be measured ??

 Assessment Values obtained when CRL is between 45-84 mm (11.3- 13.6 weeks) . This visit may be used for combined first trimester screening i.e. Double marker tests also in single visit.

 

 

What is Nuchal translucency  & nuchal thickness??

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. 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.

 

 

 

Aim of prenatal screening tests?

 

 

First, a risk-assessment test for major aneuploidies is offered to pregnant women.(Double marker & NT Scan) . In case of an increased risk, invasive diagnostic tests, entailing a miscarriage risk, are offered. For decades, only conventional karyotyping was used for final diagnosis. Moreover, several fetal ultrasound scans are offered to detect major congenital anomalies, but the same scans also provide relevant information for optimal support of the pregnancy and the delivery.

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

 

 

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 herniation, congenital heart disease, omphalocele ,skeletal dysplasias.

Smith-Lemli-Opitz syndrome

 

What is to be observed??  .

 It is the sonoluscent region at the nape of neck just behind   the surface of skin of foetus and occipital bone. It normally  generally not septated. The thickness rather than the appearance (morphology) is considered to be directly related to the incidence of chromosomal and other anomalies.

“What are the common mistakes while one is carrying out USG for NT & first trimester??

 

Correct technique for nuchal translucency measurement as a part of “First trimester of pregnancy Nasal bone, Ductus Venosus all has to be seen including blood flow of diff chambers of heart,  hard palate,  diencephalon 

 

 

 

What is normal thickness of nuchal translucency (NT) when no chromosomal abnormality is present??

 

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).  When NT Scan is combined with maternal serum markers (D markers) then it is termed as  classical first trimester Down syndrome screening (FTS, combination test) has a false-negative rate of 20–25 % and >95 % of the abnormal FTS results are false-positive,

 

: What is normal thickness of translucency??

 

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)