Handbook of Genetic Counseling/Trisomy 18

Trisomy 18

Contracting

 * What do you know about why you have been referred?
 * What do you know about the triple screen? What is your understanding of your test results?
 * What questions or concerns would you like to address today?
 * Overview of session:
 * Family and medical history
 * Explanation of maternal serum screening
 * Overview of results and what they mean
 * Explanation of genes and chromosomes
 * Information on Trisomy 18
 * Options for the future

Prenatal Intake

 * Important to obtain information on pregnancy and family history to help assess potential risks to pregnancy
 * Prenatal intake
 * How many times have you been pregnant? Any previous miscarriages or stillbirths?
 * History of infertility?
 * LMP beginning of November? EDC middle of August?
 * Any illness - infections, colds, fever, rashes?
 * Any bleeding?
 * Any exposures - X-rays (including dental), smoking, alcohol, recreational drugs, medications?
 * Any problems with pregnancy?
 * Personal background - occupation, religion, ethnicity, chronic illnesses for consultand and partner
 * Consanguinity?
 * Family history
 * Review information obtained previously
 * Any history of miscarriages, infertility, stillbirths, birth defects?
 * Other chronic illnesses, learning problems, health problems that we did not discuss?

Maternal serum screening

 * Background
 * Screening test
 * Not a diagnostic test
 * Used to identify women who are at increased risk for certain birth defects
 * These women then offered diagnostic testing
 * Negative or "normal" result does not mean that a child will not have a birth defect
 * Positive result is not a diagnosis of an abnormality
 * Can identify women at increased risk for Trisomy 21, Trisomy 18, or open neural tube defects
 * Blood test
 * Fetal and placental products can be detected in mother's blood serum during pregnancy
 * Can be offered from 14-22 weeks but most accurate at 16-18 weeks
 * Indirect measure of levels of three substances in mother's blood
 * Alpha-fetoprotein (AFP)
 * Produced by liver of fetus and excreted into amniotic fluid
 * Passes into mother's bloodstream and concentration rises gradually throughout pregnancy
 * Human chorionic gonadotropin (HCG)
 * Pregnancy hormone made by the placenta
 * Level peaks at 10 weeks and declines throughout pregnancy
 * Unconjugated estriol (uE3)
 * Hormone made by fetus and placenta
 * Level increases throughout pregnancy

Risk assessment

 * Laboratory calculates a woman's risks based on levels of three substance plus other factors
 * Gestational age
 * Marker levels change throughout pregnancy
 * Inaccurate dates are common reason for false positive
 * Gestational age can be confirmed by ultrasound
 * Maternal age
 * Multiple gestations
 * Maternal weight
 * Increased weight means increased blood volume
 * Markers will be diluted in serum and their concentration lower
 * Maternal race
 * Diabetic status
 * Insulin-dependent diabetics have increased risk for neural tube defects
 * Tend to have lower AFP levels, so use lower AFP cutoff
 * Your specific results:
 * Every pregnancy has 3-5% risk for congenital malformation
 * Background risk
 * Most of these problems cannot be detected prenatally
 * As a woman's age increases, her risk for certain birth defects increases
 * Risk figures for your pregnancy:
 * ONTD: ________
 * Down Syndrome: ________ compared to age associated risk _______
 * Trisomy 18: ________ compared to age associated risk _______
 * Screen positive for increased risk for Trisomy 18
 * Occurs when AFP, hCG, and uE3 levels are all lower than expected
 * Evaluation of screening performance
 * Up to 100 of every 1,000 women who take test will have abnormal result (up to 10%)
 * Only 3 of those 100 women will have a baby with a birth defect
 * Most abnormal test results indicate dates are wrong or another factor above has not been accurately accounted for
 * Important to remember that test cannot identify all birth defects
 * Abnormal result could be normal variation
 * Sometimes no explanation for abnormal results - increased risk for 3rd trimester complications
 * Test can detect:
 * 60% of Trisomy 18
 * 80% of ONTD
 * 60% Down Syndrome

Trisomy 18

 * Clinical picture
 * Can cause heart problems, kidney problems and other health issues
 * Usually fatal within first year of life
 * Children that survive have severe intellectual disability
 * Increased risk for pregnancy loss

Options for further testing

 * Ultrasound
 * Confirm gestational age or identify multiple fetuses to help interpret triple screen results
 * Can detect many major birth defects - rule out 95% of NTDs if visualization is not limited
 * Many fetuses with Trisomy 18 have certain "markers" that can be identified on ultrasound
 * Growth retardation
 * Single umbilical artery
 * Heart problems
 * Polyhydramnios
 * Can't diagnose chromosomal abnormalities
 * Amniocentesis
 * Performed after 15 weeks
 * Diagnostic test for some conditions
 * 99.7% accuracy for fetal chromosome analysis
 * Detects 96% of open neural tube defects by testing AFAFP
 * Cannot detect all birth defects or mental retardation
 * Risk of pregnancy loss due to procedure is 0.5%
 * Explain amniocentesis if interested
 * Insert needle into abdomen through uterus to take sample of amniotic fluid that contains cells from fetus used for karyotyping
 * Procedure:
 * Ultrasound to locate fetus and placenta
 * Abdomen cleaned with betadeine and local anesthetic (xylocaine) used to numb outer layer of skin
 * Physician inserts needle in abdomen through uterus under ultrasound guidance
 * Needle inserted 1-2 minutes
 * May feel some discomfort similar to menstrual cramp
 * Fluid is sent to lab and results ready in 1-2 weeks
 * Recommendations
 * No strenuous activity for 24 hours
 * Notify doctor if severe cramping, bleeding or leakage of fluid because there is very small risk of infection
 * Rh negative mothers should take RhoGAM

Potential Psychosocial Issues

 * Emphasize the importance of choice
 * Religious beliefs impact decisions about testing and termination
 * Anger, distrust because of family physicians advice
 * Anxiety, sadness, disbelief, fear concerning possibility of Trisomy 21
 * Provide reassurance when possible
 * Explain benefits of prenatal diagnosis to help prepare emotionally, mentally, and socially for birth of child with chromosome abnormality
 * False positive may cause unnecessary anxiety

Support Groups
Trisomy 18 Foundation at www.trisomy18.org