Some points about the Nuchal Translucency in Ultrasound according to FMF

Some points about the Nuchal Translucency in Ultrasound according to FMF

Interpretation of Mixture model in NT

1- The distribution in which NT increases with CRL:

 is the same for chromosomally abnormal and euploid fetuses but the proportion that follows this distribution is :

- - large in the euploid group (about 95%) 

- - and small in the abnormal group being about 5%, 30%, 15% and 20% for trisomies 21, 18, 13 and Turner syndrome, respectively.

2- The distribution in which NT does not change with CRL :

is firstly, small for euploid fetuses and large for the abnormal group 

and secondly, the median NT is different, 

- - being 2.0 mm for the euploid group 

- - and 3.4 mm  for trisomies 21,

- -  5.5 mm  for trisomies 18, 

- - 4.0 mm  for trisomies 13,

- - and 9.2 mm for Turner syndrome.


Fetal heart rate in:

Euploid and trisomic fetuses

In euploid fetuses the heart rate increases from about 110 bpm at 5 weeks of gestation to 170 bpm at 10 weeks and then gradually decreases to 150 bpm by 14 weeks.

In trisomy 21 the FHR is mildly increased and is above the 95th centile in about 15% of cases.

In trisomy 18 the FHR is mildly decreased and is below the 5th centile in about 15% of cases.

In trisomy 13 the FHR is substantially increased and is above the 95th centile in 85% of cases.


Fetal heart rate in:

Screening for trisomies

Inclusion of FHR in first-trimester combined sonographic and biochemical screening for chromosomal abnormalities has a small impact on the detection of trisomies 21 and 18 

but a major improvement in the detection of trisomy 13.

In addition, inclusion of FHR is important in distinguishing between trisomy 18 and 13, 

which are otherwise similar in presenting with increased fetal NT and decreased maternal serum free β-hCG and PAPP-A.


Amniocentesis should not be performed before 16 weeks because:

1- with early amniocentesis the rate of miscarriage is about 2% higher 

2- and the incidence of talipes equinovarus is 1.5% higher than after first-trimester CVS or second-trimester amniocentesis.

RelatedNews Some points about the Nuchal Translucency in Ultrasound according to FMF

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