DR/ AKRAM ABD ELGHANYDR/ AKRAM ABD ELGHANYMD MD , ALAZHAR UNIVERSITY, ALAZHAR UNIVERSITY

CONSULTANT OBS.&GYN. CONSULTANT OBS.&GYN.

PORTSAID G.HOSPITALPORTSAID G.HOSPITAL

NuchalNuchal TranslucencyTranslucency

Nuchal translucency (NT)Nuchal translucency (NT)

This is a collection of fluid under the skin behind the neck of fetuses at 11-13+6 weeks that can be measured by ultrasound examination.

The term translucency is used, irrespective of whether it is septated or not, confined to the neck, or envelopes the whole fetus. NT is increased in fetuses with chromosomal abnormalities, cardiac defects, certain genetic syndromes.

During the second trimester the translucency usually resolves or it evolves into nuchal edema or cystic hygromas with or without generalized hydrops.

Increased fetal NT thickness at 11–13+6 weeks is a common phenotypic expression of chromosomal defects and a wide range of fetal malformations and genetic syndromes.

The incidence of chromosomal and other abnormalities isrelated to the size, rather than the appearance of NT.

the correlation between nuchal translucency and fetal anomalies and perinatal risk is One ofthe single most important the single most important breakthroughs inbreakthroughs in birth defect screeningbirth defect screening

Pathophysiology of increased NT

•Cardiac dysfunction

•Venous congestion in the head and neck

•Altered composition of the extracellular matrix

•Failure of lymphatic drainage

•Fetal anemia

•Fetal hypoproteinemia

•Fetal infection.

measurememeasurementnt

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The optimal gestational age for measurement of fetal NT is 11 weeks to 13 weeks and 6 days.

The minimum fetal crown–rump length should be 45 mm and the maximum 84 mm.

Transabdominal ultrasound is successed in 95% of cases.

Transvaginal sonography in the others.

The results from transabdominal and transvaginal scanning are similar.

A mid-sagittal section of the fetus.

the fetus is in the neutral position.

Only the fetal head and upper thorax should be included in the image.

The magnification should be as large as possible.

Care must be taken to distinguish between fetal skin and amnion.

This is achieved by

spontaneous fetal movement. asking the mother to cough tapping the maternal abdomen.

The callipers should be placed on the lines that define the NT thickness .

the crossbar of the calliper merges with the white line of the border and not in the nuchal fluid.

more than one measurement must be taken.

the maximum one should be recorded.

It is good practice to retain at least one image for your patient records.

In normal fetuses NT thickness increases with fetal crown-rump length (CRL).

Increased NT refers to a measurement above the 95th centile.

The median and 95th centile of NT at a CRL of 45 mm are 1.2 and 2.1 mm. the respective values at CRL of 84 mm are 1.9 and 2.7 mm.

The 99th centile does not change with CRL and it is 3.5 mm. (Snijders et al 1998).

Screening for chromosomal defects in the first, rather than the second trimester, has the advantage of earlier prenatal diagnosis.

less traumatic termination of pregnancy.

Disadvantage of earlier screening Identifies chromosomally abnormal pregnancies that are destined to miscarry.

NUCHAL FOLDNUCHAL FOLD

The skin thickness in the posterior aspect of the fetal neck . should be distinguished from

cystic hygroma, in which the skin in this area has fluid-filled loculations. should not be confused with

nuchal translucency.

Nuchal fold measurementNuchal fold measurement

transverse section of the fetal head at the level of the cavum septum pellucidum and thalami, angled posteriorly to include the cerebellum. from the outer edge of the occiput bone to the outer skin limit in the midline.

Thickened nuchal foldThickened nuchal fold

6 mm between 18 and 24 weeks 5 mm at 16 to 18 weeks. Evaluation of the nuchal fold should be considered during the screening ultrasound at 16 to 22 weeks’ gestation.

The finding of an isolated thickened nuchal fold increases the risk for

fetal aneuploidy.

fetal karyotyping should be offered.

The prevalence of

chromosomal defects, miscarriage fetal death major fetal abnormalities. Increased exponentially with NT thickness.

chromosomal defects increases with NT thickness

50% trisomy 21. 25% trisomy 18 or 13. 10% Turner syndrome. 5% triploidy . 10% other chromosomal defects (Snijders et al 1998).

fetal NT screening identified more than 75% of fetuses withtrisomy 21 and other major chromosomal defects for a false positive rate of 5%.

the detection rate was about 60% for a false positive rate of 1% (Nicolaides 2004).

normal karyotypenormal karyotype fetal death increases with NT thickness

1.3 % with NT between the 95th and 99th centiles.

20% for NT of 6.5 mm or more20% for NT of 6.5 mm or more.

The majority of fetuses that die do so by 20 weeks and they usually show progression to hydrops.

major fetal abnormalitiesmajor fetal abnormalities

1.6%, in those with NT below the 95th centile,

2.5% for NT between the 95th and 99th centiles ,

45% for NT of 6.5 mm or 45% for NT of 6.5 mm or moremore (Souka et al 2001).

MAJOR CARDIAC DEFECTMAJOR CARDIAC DEFECT

In chromosomally normal fetuses, the prevalence of major cardiac

defects increases exponentially with NT thickness

1.6 per 1,000 for NT below the 95th centile. 1% forNT of 2.5–3.4 mm. 3% for NT of 3.5–4.4 mm. 7% for NT of 4.5–5.4 mm. 20% for NT of 5.5–6.4 mm. 30% for NT of 6.5 mm or more (Souka et al 2004).

Increased NT 99th centile constitutes an indication for specialist fetal echocardiography .

In this population the prevalence of major cardiac defects would be very high.

Body stalk anomaly

found in about 1 in 10,000 at 10–13+6 weeks. The ultrasonographic features are major abdominal wall defect, severe kyphoscoliosis, short umbilical cord with a single artery.

NT is increased in about 85% of the cases, the karyotype is usually normal.

Diaphragmatic hernia

Increased NT in 40% of fetuses. 80% of neonatal death due

to pulmonary hypoplasia . 20% of the survivors.(Sebire et al 1997).

ExomphalosExomphalos NT Increased in 85% of chromosomally

abnormal, 40% of chromosomally normal

fetuses. At 11–13+6 weeks the incidence

of exomphalos is 1 in 1,000 .the incidence of chromosomal

defects, mainly trisomy18, is about 60% (Snijders et al 1995).

MegacystisMegacystis

NT increased in

75% in chromosomal abnormalities mainly trisomy 13. 30% normal karyotype . (Liao et al 2003).

MANAGEMENT OF PREGNANCIES WITH INCREASED NT

The vast majority of fetal abnormalities associated with increased NT can be diagnosed by a series of investigations that can be completed by

14 weeks of gestation.

The parents can be reassured that The parents can be reassured that the chances of delivering a baby the chances of delivering a baby with no major abnormalities iswith no major abnormalities is

• 90% for NT between the 9590% for NT between the 95thth- 99- 99th.th. • 70% for NT of 3.5–4.4 mm70% for NT of 3.5–4.4 mm.. • 50% for NT of 4.5–5.4 mm50% for NT of 4.5–5.4 mm.. • 30% for NT of 5.5–6.4 mm.30% for NT of 5.5–6.4 mm.• 15% for NT of 6.5 mm or more.15% for NT of 6.5 mm or more.

It is possible to estimate, for each NT group, the chances of intrauterine survival and delivery of a healthy baby with no major defects.

These data are useful in counselling parents of pregnancies with increased NT and in the follow up investigations.