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
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