Nuchal translucency

 

Q.1:-Tips of measuring NT ?? Ans: The measurement of NT has to be taken 
-- In the Transcerebellar plane which includes the cerebellum, occipital bone, and cavum septum pellucidum 
-- placement of calipers from the outer edge of occipital bone to the outer edge of the skin
Cut-off For Trisomy 21 : 6 mm : DR- 33 % ;
False + ve rate (FPR)  - 0.1%
It is  measured in the sagittal plane between 11 and 14  weeks using   precise criteria.   When the nuchal translucency is increased the risk for fetal aneuploidy and various structural  anomalies – including heart  defects-  is significantly  elevated. More recent studies suggest that gestational age-specific criteria should be used, because nuchal thickness normally increases with gestational age.

Q.2:  What to do on NT >6mm?

1) Detailed Ultrasound examination of fetus for other markers/anomaly
2) Calculate the risk of aneuploidy after considering single or multiple markers based on the Study of Nicolaides et al ( I will post the table with Likelihood Ratio of each )
3) Counsel the patient & relatives with the final Risk of Trisomies..
4) Act as per patient’s wish. Non judgemental counselling

Q. 3: Relevance of NT??  Nuchal translucency evaluation a component of first trimester aneuploidy screening has had a major impact on the number  of pregnancies receiving  late first trimester ultrasound  examination . It represents the maximum thickness of the subcutaneous  translucent area between the skin  and soft tissue overlying the fetal spine at the back of the neck .

Q.4: Increased NT alone has minimal value.  Add reports of Double markers along with NT to quantify the risk of Chromosomal abnormality of foetus. Aneuploidy   screening using nuchal translucency   measurement   in conjunctions with assessment   of maternal serum human chorionic   gonadotropin and pregnancy associated plasma  protein

Q.5: What is then ,. “First Trimester  fetal anomaly detection ? “ Ans:  Assessment for selected fetal abnormalities in an “at risk pregnancy” is another indicating for first trimester  sonography  . Research in this area has focused  on anatomy visible at 11 to 14  weeks to coincide with sonography performed as a part of aneuploidy screening

 With current technology it is not realistic to expect that all major abnormalities   detectable in the second trimester may be visualized inj the first trimester. Admittedly some abnormalities may be missed at first trimester and  a  study  of systematic  anatomy   evaluation between 11 and  14 weeks in more than 40,000   pregnancies  yielded a detection  rate of  approximately 40  percent for nonchromosomal abnormalities   . This detection rate is nearly  identical to that  from a review of more than 60,000   pregnancies  from 15   studies  and is also comparable  with other reports . Identification varies considerably according to  the specific  abnormality .

Q.6:  Which abnormalities are easily detectable in first trimester??  Ans: Detection rates  are extremely high  for anencephaly , alobar holoprosencephaly  and ventral wall defects .  However   only one third  of major  cardiac  anomalies have been identified  with no detected  cases of  microcephaly or agenesis  of the corpus   callosum or say cerebellar  abnormalities,    congenital    pulmonary airway malformation or bowel  obstruction in late first trimester scan . Thus as first trimester   sonography is unreliable for detection of many major  abnormalities and therefore  It   should not  replace   second  trimester  anatomical evaluation .

Q.7: What is the relevance of Second and Third Trimester Sonography in picking up of foetal malformations??  

Ans: There are  many  indications for second and third  trimester  sonography  .There  are three types of examinations Standard. Specialized and limited

1 Standard sonographic examination is the most commonly performed Components are listed . The fetal anatomical structures that should be evaluated during the examination which are listed . May be adequately assessed  after approximately  18 weeks   when examining  twins or other multiples documentation also includes  the number  of chorion   and amnions comparison of fetal sizes  estimation of amnionic   fluid   volume   within each sac and fetal sex determination   .

There  are several types of specialized  examination . The  targeted examination is a detailed  anatomical survey  performed when an abnormality is suspected on the basis of history   screening test result or abnormal findings from the  standard examination . This detailed ultrasound scan, sometimes called the mid-pregnancy or anomaly . or   TIFFA scan or a Targeted Imaging for Fetal Anomalies .Such   atargeted examination  is performed and  interpreted by an experienced operator  . his detailed ultrasound scan, sometimes called the mid-pregnancy or anomaly scan, is usually carried out when you're between 18 and 21 weeks pregnant.

The 20-week scan is offered to everybody, but you do not have to have it if you do not want to.

The scan checks the physical development of your baby, although it cannot pick up every condition.

The 20-week scan is carried out in the same way as the 12-week scan. It produces a 2-dimensional (2-D) black and white image that gives only a side view of the baby. The NHS screening programme doesn't use 3-D or colour images.

 It includes the anatomical structures  listed below like  .  Along with   1)  additional views of   the brain  and cranium. 2)  Neck profile 3)  lungs and 4)  diaphragm  5) cardiac  anatomy   6) liver shape  7) curvature of the spine , 8) hands and feet and 9) any placental abnormalities  . The physician performing the examination further determines whether other examination components   will be needed on a case by case basis. Other  specialized  examinations include  fetal echocardiography ad Doppler   evaluation   biophysical profile and  additional   biometric measurements.