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Optional Tests: Nuchal Transluency (NT testing)

Nuchal Translucency (NT testing)


Test to find the fetal risks for Down syndrome (Trisomy 21), Trisomy 18 & 13. This test does not confirm definitely that the fetus does or does not have any of these disorders. It is possible to have a false positive approximately 5% of the time.

NT is performed by measuring the fluid at the back of the fetal neck by ultrasound between 11-14 weeks.  Blood is drawn from the mother’s arm to check the levels of beta-hCG and PAPP-A.  Beta-hCG and PAPP-A (pregnancy-associated plasma protein) are both produced by a newly fertilized egg.
These chromosomal defects increase in frequency as the mother’s age increases and with fertility treatments.  



DNA & Chromosomes

The nucleus or core of every cell in the body contains a person’s DNA.  DNA is made up of 23 pairs of chromosomes inherited ½ from the mother and ½ from the father for a total of 46 chromosomes.  Chromosomal genetic disorders occur when cells does not split and replicate properly either leaving only and individual chromosome or 3 chromosomes instead of the normal pair.


Normal Human Chromosomal Pairs


Down syndrome (Trisomy 21)

The most common chromosomal defect
Occurs when the DNA has 3 copies of chromosome 21
Occurs 1 in every 800 newborns
Life expectancy can be up to 60 years
Defects may include:
  • Congenital heart defects
  • Breathing problems
  • Hearing problems
  • Intestinal problems
  • Vision problems
  • Skeletal problems
  • Thyroid conditions
  • Increased risk for childhood leukemia
  • Increased risk for Alzheimer’s
        Incidence of Down by Maternal Age   

Maternal Age

Down syndrome rates

Maternal Age

Down syndrome rates

Maternal Age

Down syndrome rates

20

1 in 2000

30

1 in 900

40

1 in 100

21

1 in 1700

31

1 in 800

41

1 in 80

22

1 in 1500

32

1 in 720

42

1 in 70

23

1 in 1400

33

1 in 600

43

1 in 50

24

1 in 1300

34

1 in 450

44

1 in 40

25

1 in 1200

35

1 in 350

45

1 in 30

26

1 in 1100

36

1 in 300

46

1 in 25

27

1 in 1050

37

1 in 250

47

1 in 20

28

1 in 1000

38

1 in 200

48

1 in 15

29

1 in 950

39

1 in 150

49

1 in 10




.

Trisomy 18 (Edward's Syndrome)

2nd most common chromosomal defect
Occurs 1 in every 3,000 newborns
Occurs when the DNA has 3 copies of chromosome 18

Most severe chromosomal abnormality
Complications are life-threatening to fetus and 50% carried to delivery are still born.  Less than 10% will survive 1 year after birth.
Defects may include:
  • Heart defects
  • Kidney problems
  • Intestines outside of the abdomen (gastroschisis)
  • Esophagus doesn’t connect to stomach (esophageal artesia)
  • Fluid in the brain (hydrocephaly)
  • Small head (microcephaly)
  • Clenched hands
  • Low set ears


Trisomy 13 (Patau syndrome)

Occurs when the DNA has 3 copies of chromosome 13
1 in every 10,000 newborns

Defects may include:
  • Congenital heart defects
  • Rotation of internal organs
  • Deafness
  • Cleft palate or lip
  • Clenched hands, extra fingers or toes
  • Close-set eyes
  • Hernias (inguinal or hiatal)
  • Severe mental retardation
  • Seizures
  • Small head (microcephaly)


What are the options if the NT shows an increased risk?


Remember that an increase risk result on NT testing does not confirm the fetus has a disorder.  We offer to refer patients for genetic counseling and review all the options.    
  • A woman can choose to do nothing different, carry the pregnancy to term, deliver and have the newborn assessed for any chromosomal defects.  Miscarriage may also occur when a fetus has a Trisomy disorder.
  • A level 2 ultrasound can be performed to look for any disorders link with Trisomy.  This ultrasound will target areas such as the heart, head, brain, kidneys, hands and feet
  • There are 2 tests that can give a definitive diagnosis by evaluating the DNA of the fetus.  Both tests have risks for miscarriage.
    • CVS (chorionic villus sampling) between 10 -13 weeks

A sample of placental tissue is obtained with a thin needle either through the abdomen or through the vagina and cervix. Miscarriage occurs 1 in 200.

http://www.daviddarling.info/encyclopedia/C/chorionic_villus_sampling.html

    • Amniocentesis between 15-20 weeks

A sample of the amniotic fluid around the fetus is obtained with a needle through the abdomen.  Miscarriage occurs 1 in 400.


http://healthforlifeblog.com/special-tests-that-detect-birth-defects-during-pregnancy



Cyndi Ayoub, WHNP
Created March 16, 2011
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