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

http://www.ndss.org/index.php?option=com_content&view=article&id=61&Itemid=78

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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.