Genetics and Fetal Assessment

Question 1

Carrier screening

Answer 1

• 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

Question 2

Targeted Carrier Testing

Answer 2

• Based on a positive family history
• Disorder is common (Fragile X) or rare

Question 3

Population-based Carrier Screening

Answer 3

Carrier screening offered to everyone in the general population

Question 4

Ethnicity-based Carrier Screening

Answer 4

Carrier screening offered only to particular ethnic groups determined to be at higher risk for specific genetic disorders

Question 5

Expanded Carrier Screening

Answer 5

• Screening panels capable of assessing hundreds of causal mutations for genetic disease.
• Test all individuals for the same conditions, regardless of ethnicity

Question 6

Screening vs. diagnostic testing

Answer 6

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

Question 7

Nuchal Translucency Screen

Answer 7

• 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

Question 8

Quad Screen AKA maternal serum screen

Answer 8

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%

Question 9

Non-Invasive Prenatal Testing

Answer 9

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

Question 10

Chorionic villus sampling VS Amniocentesis

Answer 10

• 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

Question 11

Nursing care following invasive testing: Before the procedure

Answer 11

• Explain the procedure and potential complications
• Obtain informed consent
• Fill/empty bladder*
• Review blood type
• Ultrasound guides the needle

Question 12

Nursing care following invasive testing: After the procedure

Answer 12

• 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

Question 13

Detailed anatomy u/s 18-20 weeks

Answer 13

• 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

Question 14

Fetal Heart Rate Monitoring Timing

Answer 14

Normally 32 weeks and above

Question 15

Purpose of Fetal Heart Rate Monitoring

Answer 15

• 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)

Question 16

Non stress test

Answer 16

• 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

Question 17

How to measure contractions

Answer 17

from the start of one contraction to the start of the next contraction = frequency of contraction

Question 18

Mild contractions

Answer 18

Palpate the fundus and it feels like your nose

Question 19

Moderate Contractions

Answer 19

Palpate the fundus and it feels like your chin

Question 20

Severe Contractions

Answer 20

Palpate the fundus and it feels like your forehead

Question 21

Moderate Variability

Answer 21

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).

Question 22

Causes of Minimal Variability

Answer 22

• Hypoxemia/acidosis
• Fetal sleep cycle
• Drugs (i.e., narcotics)
• Anomalies (CNS or cardiovascular)

Question 23

Marked variability

Answer 23

A sign of acute hypoxia and prompts the OB team to identify and correct the cause

Question 24

Accelerations

Answer 24

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.

Question 25

Early Deceleration

Answer 25

Correspond to the contractions; they are mirror images. They are a benign reflex –a vasovagal response to fetal head compression that alters cerebral blood flow and stimulates vagal nerve. They are NOT associated with fetal hypoxemia or acidosis.

Timing of the peak and timing of the nadir match up

Question 26

Late Deceleration

Answer 26

Look a lot like early decelerations; however, they occur AFTER the peak of the contraction. They represent problems with uterine perfusion (uteroplacental insufficiency) and ARE associated with fetal hypoxemia/acidemia. Uterine contractions result in decreased blood flow within the intervillous space of the placental bed. This results in less exchange of nutrients/waste (aka decreased maternal fetal oxygen transfer.

Question 27

Variable Deceleration

Answer 27

Are SUDDEN/ABRUPT drops in fetal heart rate, often appearing as V, U, or W. They may or may not occur related to a contraction. They VARY in their timing and appearance (hence, variable). They occur because of umbilical cord compression, resulting in decreased venous return to the fetal heart rate. This results in a decrease in fetal heart rate as it has to slow to allow for adequate filling time of the heart. In other words, the garden hose is kinked, so it takes longer to fill the bucket…

Question 28

Acronym for Non-Stress Test: VEAL CHOP

Answer 28

Variable Cord compression
Early Head compression
Accelerations Okay O2
Late Placenta insufficiency

Question 29

Nonstress test fetal heart rate components: Variability

Answer 29

Fluctuations in fetal heart rate from baseline (amplitude)
Absent
Minimal
Moderate
Marked

Question 30

Biophysical Profile

Answer 30

• NST plus Ultrasound evaluation
• Assesses five parameters: FHR, Fetal breathing movement (FBM), Gross fetal movements, Fetal tone, Amniotic fluid volume (AFV)
• Normal score is 8-10

Question 31

Contraction Stress Test

Answer 31

Evaluates FHR in response to contractions initiated by endogenous (nipple stimulation) or exogenous oxytocin (IV)

Question 32

Interpretation of Contraction Stress Test:

Answer 32

• Negative—no late decelerations with at least three contractions lasting 40–60s in a 10-min period
• Positive—late decelerations with at least 50% of contractions; potential fetal risk and cesarean may be necessary
• Suspicious—late decelerations in less than half of contractions; other testing and/or repeat stress test in 24 h
• Unsatisfactory—inadequate contraction pattern or tracing; continue test or repeat after mother rests

Question 33

Percutaneous Umbilical Blood Sampling (pubs)

Answer 33

Aspirates cord blood to test for genetic conditions, chromosomal abnormalities, fetal infections, hemolytic or hematological disorders