N T as per Foeatal Medicine foundation (UK) FMF -Website is there

 

Technique to Measure the NT According to the Fetal Medicine Foundation.

Section : Midsagittal ( visualization of the fetal profile nasal bone and tip of the nose diencephalon NT and exclusion of the frontal processes of the upper maxilla also defined as zygomatic bones)

Magnification : Fetal head and upper thorax occupy the whole screen.

Fetal position: The fetus must be facing up with the neck in a neutral position neither hyperextended nor hyperflexed as there could be a consequent overestimation or underestimation of the NT measurement respectively .

Settings: Ultrasound and transducer settings should be optimized in order to clearly visualize the lines representing the borders of the nuchal space with enough contrast to have no artifacts with in translucency.

Calipers positioning ;: “on to on “ ; the inner border of the horizontal crossbar of the calipers and the inner border of the two retronuchal lines should be perfectly superimposed ; the horizontal crossbar should not be entirely embedded within the retronuchal white lines and conversely no part of it should be within the black nuchal translucency space.

It is important before measuring to identify the amniotic membrane in order to avoid wrong measurements of the space between skin and amnion. In order to obtain a proper midsagittal view it is necessary to search for the anatomic landmarks described above visible just in this section. The exclusion of the cerebral lateral ventricles and the evidence of the structures of the posterior fossa (brainstem fourth ventricle and cysterna magna ) could be additional anatomic details to achieve a more accurate midsgittal section. The ultrasonic beam should be perpendicular to the lines of the NT in order to have a clear image of the edges of these lines and gain reduction could allow to get read of the fussiness on the edges of these lines and the artefacts insides the translucency .

The measurement has to be taken on the thickest part of the NT being careful to place the calipers on the lines defining the NT rather than the amnion. It is recommended to repeat the procedure to obtain more than one measurement and then choose the biggest correct measurement.

Dilemma 5: If U cord is around the neck?? Sometimes the umbilical cord is positioned around th fetal neck (nuchal cord) making technically difficult the measurement . The presence of a nuchal cord usually causes compression on the skin of the neck with subsequent redistribution of the nuchal fluid above ( increased ) and below ( reduced ) the compression site. In this case it is recommendable to measure above and below the cord and to use the average between these two measurements to calculate the risk. 

Dilemma 6: Interpretation of too much NT ?? What may be possibilities?? . Nuchal translucency thickness usually increases with gestational age with 1.5 mm and 2.5 mm being the 50^th and 95^th percentile respectively for gestational ages between 10 and 12 weeks 2.0 mm and 3.0 mm are the 50^th and 95^th percentile respectively for gestational ages between 12 and 14 weeks. Therefore undersatdably, Nuchal translucency thickness usually increases with gestational age.  But any thickening of the nuchal translucency prompts us  to a diagnosis of A) cystic hygroma , B) chromosomal abnormalities or C) cardiac abnormalities

 

Dilemma 8:  What is the relevance of NT ?  Nuchal translucency measurement has become an integral part of singleton pregnancy evaluation. In addition to A) aneuploidy abnormal NT measurements have been shown to be associated with B)  fetal congenital heart disease and C) other anatomic abnormalities .

Dilemma 9:  What about twins?? Ans: Studies evaluating the quality of NT measurements in multiple gestations have shown that there is no significant difference between image qualities in singleton versus multiple gestations. One Caveat:-However as would not be unexpected the fetuses that are located furthest from the uterine wall in multiple gestations are more difficult to evaluate and have poorer image scores. Importantly NT distributions and cut off values do not differ between singleton and multiple gestations and can therefore be used for evaluation with the same sensitivity. Abnormal NT evaluation in twin gestations has been shown to be associated with future development of twin twin transfusion and discordance for anomalies.

What about Double marker tets done concurrently??  Ans: Maternal serum analyte (marker ) interpretation in conjunction with NT measurement is commonly used in singleton gestations with A) free beta human chorionic gonadotropin and B)  pregnancy associated plasma protein A . These two along with  NT having a 90 % detection rate with a 5 % false positive rate.

 

What about in multiple pregnancies ?? However the Fetal Medicine Foundation found a decrease to 75 % in dizygotic pregnancies discordant for trisomy . Second trimester serum analyte has also been shown to have a decreased detection rate in multiple gestation as compared with singletons. In conclusion serum screening tests in multiple pregnancy have not been found to be as sensitive in singletons. Nuchal translucency  alone offers a better detection rate and can be followed up with early diagnostic testing.