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Didascalia

When the thickness of the fluid in the back of the fetus’s neck is increased (increased nuchal translucency), a qualified practitioner can help the patient in choosing the best way to manage her pregnancy 

 

 

The measurement of nuchal translucency will vary depending on the gestational age.

Generally it is said that the thickness is increased when it is above 2.5 mm. However this is valid only when the measurement is taken when the size of the fetus is 45-60mm, while it is considered to be normal if measurement is taken when the fetus is more than 70mm long.

 There are many reasons why the nuchal translucency is increased.

The incease of NT is associated with:

  • Trisomy 21 and other chromosomal defects
  • Over 50 fetal malformations and genetic syndromes
  • Increased risk for fetal intrauterine death

 Once it has been confirmed that the NT measurement is increased (assuming that the measurement is conducted by following the criteria described in this website), the main objective lies in differentiating fetuses with chromosomal or structural anomalies, from those that are likely to have normal development.

 

As illustrated in the table, there is a positive correlation between an increased nuchal translucency and risk for chromosomal defects or other pathologies


 

 

 

 

:defined as less than 2.5 mm

 

:between 2.5- 2 3.4 mm

 

 

 

 


A POSITIVE test result does not imply that the fetus has an abnormality but it is advised to have further investigation.

A positive risk for T21 or other trisomies is when the risk is higher than 1/100. Therefore a risk of 1/90 is positive and 1/110 is negative.

Before concluding that the test is positive, it is important to take into account other markers such as

nasal bone,facial angle,tricuspid  and ductus, which when included with the measurement of NT and blood test results, help to increase the test’s detection rate.

The practitioner should help the patient understand the reasons or factors in the test that have contributed to an increased risk:

  • is caused only by an increased nuchal translucency
  • is due to the analysis of the hormones in the maternal blood while the nuchal translucency is normal.
  • The nuchal translucency is increased and the bloood test is also abnormal

Both nuchal translucency and blood test contributed to a positive test:

In this case, with both increased nuchal translucency measurement and positive blood results, it is more likely that the fetus has a chromosomal abnormality. In cases of structural anomalies, blood results will not vary.

PROCEDURE TO BE FOLLOWED WHEN A TEST IS POSITIVE

The diagram a practitioner should follow with high risk pregnancies is as follows: 

 

 

      *From  2013 in case of result that suggest intermediate or high risk a non invasive test can be offered  (Harmony prenatal test™)

If no fetal defects have been identified the parents should be reassured of the fact that the fetus has good prospect of being born and develop normally.

In these cases, the risk of malformation or problems of neurological development, should be comparable to that of the general population.

 

In cases where there is a family history of  genetic syndromes

  • If they can be analyzed through DNA testing, this should be done using the sample taken with amnio/villocentesis
  • A detailed ultrasound scan should be conducted at 11-13 weeks with the aim of identifying major fetal anomalies and signs that can indicate a genetic syndrome.
  • Another cardiac scan should be done at two weeks later and another at 23 weeks.

If at 14-16 weeks the measurement of NT remains high but there are no evident fetal anomalies or there is an indication of an evolution towards a nuchal edema or fetay hydropes at 20-22 weeks, the possibility of a congenital infection or genetic syndrome must be considered.

  • Consideration should be given to maternal serology for toxoplasmosis, cytomegalovirus and parvovirus B19
  • To monitor the development of nuchal edema, ultrasound examinations should be performed every 4 weeks
  • DNA analysis should be performed to check for genetic syndromes such as Noonan syndrome. This should be done even where there is no family history of a syndrome.
  • In these cases, pre-natal death and risk or genetic syndrome in the ones that are born alive, is approximately 20%.
  • Late neurological development is about 3-5%
Last Edit: 05/08/2013 9:12pm
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