Genetic Screening vs Genetic Diagnostic Testing

Screening tests show the “chance” that a developing fetus has a certain genetic condition.

– Screenings may be noninvasive (ultrasound, blood work) where the fetus is not directly exposed to any risks

Diagnostic tests will show if the developing fetus has a certain genetic abnormality or condition

– Testing is invasive, (inserting needles to aspirate samples) where there is increased risk of miscarriage . (WebMD 2014)

Why Performed A Genetic Test?

•To screen and diagnose any existing problems that may affect the mother's or baby's health

•Identify and address problems as they arise

•Assess the risk of a baby having a chromosomal or genetic abnormality (labtestsonline.org 2014)

Who should receive Genetic Testing?

• Women age 35 and older (Advanced Maternal Age)• Abnormal results from prenatal screening tests, (ultrasound and blood

work)• Exposure during pregnancy; such as medications or infections• Family history of a genetic condition• Previous experience of multiple miscarriages• Experiencing infertility• Known carriers of a genetic condition (John Hopkins 2015)

Different Types of Genetic Screening/TestingPurpose Test Name Why performed When

performedWho

performed on

Genetic tests for inherited diseases

Genetic testing for inherited disease

Check carrier status for certain genetic diseases to determine risk of having a baby with disease

Pre-conception or first trimester

Mother and father (blood sample)

Genetic testing for hemoglobin disorders

Check carrier status for certain hemoglobin disorders to determine risk of having a baby with disease

Pre-conception or during pregnancy

Mother and father(blood sample)

Cystic fibrosis carrier testing

Check carrier status for CF Pre-conception or first trimester

Mother and father(blood sample) (labstestsonline.org 2014)

Genetic Screening - Fetal RiskPurpose Test Name Why performed When performed Who performed

on

Detection of fetal risks

First trimester Down Syndrome Screen

Assess risk of carrying a fetus with certain chromosomal abnormalities, such as Down Syndrome

Usually between 10 weeks, 4 days and 13 weeks, 6 days of pregnancy

Mother (blood sample plus ultrasound)

Triple marker or Quad Marker Screen(MSAFP)

Assess risk of carrying a fetus with certain chromosomal abnormalities and open neural tube defects

Between 15 and 20 weeks of pregnancy

Mother (blood sample)

Cell-free fetal DNA

Assess risk of carrying a fetus with certain chromosomal abnormalities; currently recommended for women at high risk of having babies with these disorders

During or after the 10th week of pregnancy

Mother (blood sample) (labstestsonline.org 2014)

Genetic Testing - Fetal AbnormalitiesPurpose Test Name Why performed When performed Who performed

on

Detection of fetal abnormalities

Chorionic Villus Sampling (CVS)

Detect chromosomal disorders in the fetus

Between weeks 10 and 12 of pregnancy, if recommended

Mother (cells from the placenta)

Amniocentesis Detect certain birth defects and chromosomal abnormalities

Between 15 and 20 weeks of pregnancy, if recommended

Mother (amniotic fluid)

Percutaneous Umbilical Blood Sampling (PUBS) aka Cordocentesis

Detect chromosome abnormalities, blood disorders, and certain infections

Between weeks 18 and 22 of pregnancy, if recommended

Mother/fetus (fetal blood sample obtained from vein in the umbilical cord) (labstestsonline.org 2014)

Chorionic Villus Sampling

(Mayo Clinic 2010)

Method of access is determined by fetal position

The chorionic villus tissue located

Can be performed through transcervical or

transabdominal method

Sample of CV tissue is obtained & evaluated for

genetic abnormalities

An ultrasound is used to guide procedure

Fetus may be located in posterior, anterior or fundal position

What to expect from a CVS Test?

Chorionic Villus Sampling

Clinical Significance of Chorionic Villus Sampling

Chromosomal defects such as:•Down syndrome, trisomy 13, trisomy 18

•Sex chromosome abnormalities like Turner syndrome and Klinefelter syndrome;

•Genetic disorders such as Tay-Sachs disease, hemophilia, sickle cell disease or cystic fibrosis.

•The sex of the baby if you might have a gender-related genetic disorder such as hemophilia, which a mother only passes to her male children.

•Unlike amniocentesis, CVS cannot detect neural tube defects such as spina bifida. The test can also not check the development of the baby's lungs. (Women & Infants 2014)

Nursing Considerations for a Chorionic Villus

Sampling • Administer RhoGAM if the woman is Rh negative as

the maternal circulation may be exposed to fetal blood

• Promote fluids and instruct the patient to refrain from voiding- a full bladder helps the provider access

• A small amount of bleeding is common after the transcervical procedure but monitor for excessive bleeding

• Genetic counseling is recommended prior to the CVS (Hecher et. Al 1994)

Amniocentesis

(Mayo Clinic 2010)

Abdomen is cleansed with an antiseptic

Sterile needle is inserted into uterine cavity through

maternal abdomen removing a small amount of amniotic fluid

Performed under Ultrasound Guidance

Performed between 15 to 20 weeks gestation

Undress from waist down, (in hospital gown)

What to expect from a

Amniocentesis Test

Amniocentesis

Clinical Significance of Amniocentesis

• An amniocentesis may be used for genetic and chromosome testing in the second trimester of pregnancy in the presence of one or more of these conditions:

• Family history or previous child with a genetic disease or chromosomal or metabolic disorder

• Risk of open neural tube defects (ONTDs), such as Spina Bifida

• Maternal age over 35 years by the pregnancy due date

• Abnormal maternal screening tests, such as maternal serum alpha fetoprotein level (MSAFP)

• Risk of a sex-linked genetic disease (Women & Infants 2014)

Nursing Considerations for a Amniocentesis

• Informed consent

• Have clients empty bladder before amniocentesis

• Baseline vital signs and FHR, then check every 15 minutes

• Position supine with abdominal scrub

• Encourage bed-rest and avoidance of strenuous activities

• Instruct client to report any side effects, chills, fever, fluid leakage, decreased fetal movement and uterine contractions (Women & Infants 2014)

PUBS

(Mayo Clinic 2010)

Abdomen is cleansed with an antiseptic

The ultrasound guides the thin needlethrough the

abdomen and uterine walls to the umbilical cord. The

needle is inserted into the umbilical cord to retrieve a

small sample of fetal blood.

Performed under Ultrasound Guidance

Performed before 24 weeks gestation

Undress from waist down, (in hospital gown)

What to expect from a PUBS Test

Percutaneous Umbilical Blood Sampling(PUBS)

Clinical Significance of Percutaneous Umbilical Blood

Sampling

• PUBS detects chromosome abnormalities (i.e. Down Syndrome and blood disorders (i.e. fetal hemolytic disease.)

• PUBS may be performed to help diagnose any of the following concerns:– Malformations of the fetus– Fetal infection (i.e. toxoplasmosis or rubella)– Fetal platelet count in the mother– Fetal anemia– Isoimmunization

• This test is different from amniocentesis in that it does not allow testing for neural tube defects. (Americanpregnancy.org 2014)

Nursing Considerations for a Percutaneous Umbilical

Blood Sampling• Informed consent

• Have clients empty bladder before cordocentesis

• Baseline vital signs and FHR, then check every 15 minutes

• Position supine with abdominal scrub

• Encourage bed-rest and avoidance of strenuous activities

• Instruct client to report any side effects, fever, blood loss from puncture site or leakage, decreased fetal movement, drop in FHR, PROM (Americanpregnancy.org 2014)

References• American Pregnancy Association (July 2015) Cordocentesis: Percutaneous Umbilical Blood

Sampling (PUBS) Retrieved from: http://americanpregnancy.org/prenatal-testing/cordocentesis/ Accessed on: November 8, 2015

• Davidson, Michele, London, Marcia, Ladewig, Patricia (2016) Olds Maternal-Newborn Nursing & Women’s Health Across the Lifespan Pearson Education, Inc.

• Kee, Joyce LeFever (2014) Laboratory and Diagnostic Tests with Nursing Implications Ninth Edition, Pearson Education, Inc. Upper Saddle River, New Jersey 07458 pg. 528 – 531 cordocentesis, 457 – 458 amniocentesis, 486 – 487 chorionic villi biopsy (CVB)

• Lab Tests Online Organization (December 2014) Pregnancy & Prenatal Testing Retrieved from: https://labtestsonline.org/understanding/wellness/pregnancy/ Accessed on: November 3, 2015

• WebMD (March, 2014) Genetics-Prenatal Screening Retrieved from: http://www.webmd.com/a-to-z-guides/genetics-prenatal-screening-and-testing Accessed on: November 2, 2015

• John Hopkins Hospital (2015) Genetic Counseling: Prenatal Diagnosis and Treatment Center Retrieved from: http://www.hopkinsmedicine.org/gynecology_obstetrics/specialty_areas/maternal_fetal_medicine/services/genetic_counseling_prenatal_diagnosis_treatment_center.html Accessed on: November 1, 2015

• Women & Infants (2014) Chorionic Villus Sampling Retrieved from: http://www.womenandinfants.org/pdc/chorionic-villus-sampling.cfm Accessed on: November 8, 2015

• Hecher, K., Campbell, S., Doyle, P., Harrington, K., & Nicolaides, (1994) K. Assessment of fetal compromise by doppler ultrasound investigation of the fetal circulation. Circulation. 91, 129-138. Retrieved from: http://circ.ahajournals.org/content/91/1/129.full Accessed on November 8, 2015