Genetics and Fetal Assessment Flashcards
Carrier screening
- Recessive conditions
- 25% risk in each pregnancy if BOTH parents are carriers
- Option of prenatal diagnosis or diagnosis at birth if pregnancy at risk
- Not ALWAYS informative
- Can be performed anytime—ideal time: pre-conception
- Testing parent’s DNA—only need to complete once
Targeted Carrier Testing
- Based on a positive family history
- Disorder is common (Fragile X) or rare
Population-based Carrier Screening
Carrier screening offered to everyone in the general population
Ethnicity-based Carrier Screening
Carrier screening offered only to particular ethnic groups determined to be at higher risk for specific genetic disorders
Expanded Carrier Screening
- Screening panels capable of assessing hundreds of causal mutations for genetic disease.
- Test all individuals for the same conditions, regardless of ethnicity
Screening vs. diagnostic testing
Screening provides a personalized risk assessment
- Odds
- No risk to the pregnancy
- Can be incorrect
Diagnostic testing provides a yes or no answer
- Definitive diagnosis
- Gives you yes or no
- Samples pregnancy tissue with a needle
- Have to know what to look for
Nuchal Translucency Screen
- Also known as 2-week screen
- Ultrasound screen
- 11w13w6d GA
- 90% detection rate
- If abnormal, associated with: Chromosome abnormalities, Genetic syndromes, Heart defects, Skeletal dysplasia
Quad Screen AKA maternal serum screen
Down syndrome, trisomy 18, open neural tube defects (oNTDs)
Timing: 15-21 weeks (ideally 16-18 weeks); VERY dependent on accurate gestational age
Detection rate: Down syndrome, trisomy 18, oNTDS: ~80%; False positive rate: 5%
Non-Invasive Prenatal Testing
Fetal cell-free DNA in mom’s circulation
- Quantification of DNA (“counting”)
- As early as 9 weeks GA
Highest detection rate available for
- Down syndrome (>99%)
- trisomy 18 (>98%)
- trisomy 13 (79-99%)
Internal blood draw
A screening NOT a test
Chorionic villus sampling VS Amniocentesis
- DNA/Chromosome analysis and/or single gene testing, amniotic fluid testing for infection, AFP
- Risk of bleeding, infection, premature rupture of membranes, amniotic emboli, Rh isoimmunization, fetal injury, or spontaneous abortion.
- CVS has higher risk for miscarriage because it is taking snippets of the pregnancy
Nursing care following invasive testing: Before the procedure
- Explain the procedure and potential complications
- Obtain informed consent
- Fill/empty bladder*
- Review blood type
- Ultrasound guides the needle
Nursing care following invasive testing: After the procedure
- Assess fetal heart rate
- Administer Rh Immunoglobulin*
- Education regarding warning signs: fever, cramping, leakage of fluid, and vaginal bleeding
- Limit activity for 24-48 hours
- Offer support and reassurance
Detailed anatomy u/s 18-20 weeks
- 3D ultrasound
- At 20 weeks, they look head to toe to look for anomalies
- Can look for placenta issue and look at the fluid
- Doppler measurements
Fetal Heart Rate Monitoring Timing
Normally 32 weeks and above
Purpose of Fetal Heart Rate Monitoring
- Assess for uterine-placental dysfunction resulting in decreased O2 delivery and hypoxia
- Allows for identification of fetus at increased risk of harm
- May be noninvasive (external) or invasive (internal)
- Antepartum (Non-Stress Test) vs Intrapartum (Continuous EFM)
Non stress test
- Evaluates: uteroplacental sufficiency by noting FHR accelerations in association with fetal movement
- Indicates: adequate oxygenation, healthy neural pathway from the fetal CNS to the heart and ability of fetal heart to respond to stimuli
- Normal fetus will have characteristic fetal heart rate patterns in response to fetal movements
How to measure contractions
from the start of one contraction to the start of the next contraction = frequency of contraction
Mild contractions
Palpate the fundus and it feels like your nose
Moderate Contractions
Palpate the fundus and it feels like your chin
Severe Contractions
Palpate the fundus and it feels like your forehead
Moderate Variability
In a healthy fetus, there is constant interplay between the sympathetic (accelerates) and parasympathetic (decelerates) nervous system on control of heart rate. This occurs through the cerebral cortex, medulla, sympathetic ganglia, and vagus nerve. The interaction causes a variability (scratchiness) to the fetal heart rate tracing. At term, moderate variability is normal as it indicates a normally functioning CNS. Variability is an important indicator of adequate oxygenation. Conditions that affect CNS-cardiovascular system (i.e., opioids) can affect variability (i.e., decrease it).
Causes of Minimal Variability
- Hypoxemia/acidosis
- Fetal sleep cycle
- Drugs (i.e., narcotics)
- Anomalies (CNS or cardiovascular)
Marked variability
A sign of acute hypoxia and prompts the OB team to identify and correct the cause
Accelerations
Are reflective of a well oxygenated fetus. The presence of two in a 20-minute period, with moderate variability and no decelerations is a reactive non stress test.
