Assessment of High-Risk Pregnancy: Fetal Assessment and Genetic Screening (Chapter 26)

Daily Fetal Movement Counts (Kick Counts)

• Purpose: To assess fetal oxygenation and overall well-being.
• Timing: This assessment typically begins at $28$ weeks of gestation.
• Normal Findings:   - The presence of $\ge 10$ movements within a $2$ hour period.   - Testing should occur at the same time twice daily or more frequently.   - The mother should sit comfortably or lie on her side during the count.
• Abnormal Findings:   - Decreased movement is a significant indicator that requires further testing.   - Follow-up includes a Non-Stress Test (NST) or a Biophysical Profile (BPP).   - The patient should seek medical help immediately if movement decreases.

Maternal Serum Screening (Genetic Screening)

• Timing: 9 – 10 weeks:   - Cell-Free Fetal DNA: Used to screen for chromosome abnormalities.
• Timing: 11 – 14 weeks:   - PAPP-A, hCG, and Nuchal Translucency: Primary screening indicators for Trisomy $21$ (Down Syndrome).
• Timing: 16 – 18 weeks:   - Maternal Serum Alpha-Fetoproteins (AFP): Used specifically for screening for neural tube defects (NTDs).   - Follow-up for abnormal results involves Ultrasound (US) and confirmation via amniocentesis.
• Timing: 15 – 21 weeks:   - Quad Screen: Screens for Trisomy $18$ and Trisomy $21$.   - Components: MSAFP, unconjugated estriol, hCG, and dimeric inhibin A.

Ultrasound

• First Trimester Timing (Transvaginal Ultrasound):   - Purpose: Confirm pregnancy and viability.   - Purpose: Determine the number of fetuses.   - Purpose: Dating of the pregnancy.   - Measurements: Includes Nuchal Translucency, head measurements, and crown-rump length.
• Timing: 18 – 22 weeks:   - Purpose: Maternal anatomy assessment.   - Purpose: Anatomy scan of the fetus.   - Purpose: Assessment of the placenta and amniotic fluid levels.
• Second and Third Trimester Timing:   - Purpose: Monitor cervical length, fetal growth, and fetal anatomy.   - Purpose: Determine fetal position and assess fetal well-being.   - Purpose: Evaluate amniotic fluid and the placenta.
• Procedural Visualization:   - Ultrasound is utilized for visualization during Chorionic Villus Sampling (CVS), amniocentesis, and Percutaneous Umbilical Cord Sampling (PUBS).
• General Purposes:   - Detect structural abnormalities.   - Assess fetal growth patterns.   - Evaluate the volume of amniotic fluid.

Non-Stress Test (NST)

• Purpose: To assess fetal oxygenation by observing the Fetal Heart Rate (FHR) response to fetal movement.
• Timing: Conducted in the third trimester, particularly for high-risk pregnancies.
• Normal (Reactive) Interpretation:   - $\ge 2$ accelerations within a $20$ minute window.   - Accelerations must be $\ge 15\,bpm$ above the baseline.   - Accelerations must last for $\ge 15\,seconds$ (applicable for pregnancies $\ge 32$ weeks).
• Abnormal (Non-reactive) Interpretation:   - Occurs when the test lacks sufficient accelerations.   - Intervention: Extend the testing time for an additional $20$ minutes.   - Methods to Stimulate Fetus: Manual stimulation, providing juice to the mother, or vibroacoustic stimulation (if the fetus is in a sleep state).   - Follow-up: Requires a Biophysical Profile (BPP) or a Contraction Stress Test (CST).

Biophysical Profile (BPP)

• Purpose: To assess fetal oxygenation and Central Nervous System (CNS) function.
• Components: Combined assessment using Ultrasound and the Non-Stress Test.
• Modified BPP: Consists only of the NST and the Amniotic Fluid Index (AFI).
• Timing: Performed in the third trimester.
• Scoring System (5 Components, 2 points each):   - Non-Stress Test (NST):     - Score $2$: Reactive.     - Score $0$: Non-reactive.   - Fetal Breathing Movement (FBM):     - Score $2$: At least one episode of fetal breathing movement lasting at least $30$ seconds within a $30$-minute observation.   - Fetal Movement:     - Score $2$: At least three trunk or limb movements within $30$ minutes.   - Fetal Tone:     - Score $2$: At least one episode of active extension with return to flexion of a fetal limb or trunk; opening and closing of the hand is considered normal tone.   - Amniotic Fluid Index (AFI):     - Normal Range: $5-25\,cm$.     - Oligohydramnios: Less than $5\,cm$.     - Polyhydramnios: More than $25\,cm$.     - Score $2$: Deepest vertical pocket is $> 2\,cm$.     - Score $0$: Deepest vertical pocket is $< 2\,cm$.
• Interpretation of Total Score:   - 8 – 10: Normal result.   - 6: Equivocal; suspect chronic asphyxia.   - 4 or less: Abnormal; strongly suspect chronic asphyxia; likely necessitates delivery.

Amniocentesis

• Timing:   - 15 – 20 weeks: Performed for genetic diagnosis.   - After 32 weeks: Performed to assess fetal lung maturity.
• Indications:   - Second trimester: Diagnosis of genetic disorders or congenital anomalies.   - Third trimester: Evaluation of fetal lung maturity.
• Risks:   - General: Infection, fluid leakage, fetal injury, and miscarriage.   - Maternal: Rh sensitization and fetomaternal hemorrhage with possible maternal Rh isoimmunization.   - Management: Administer RhoGAM to Rh-negative mothers.

Chorionic Villus Sampling (CVS)

• Timing: $10 – 13$ weeks.
• Purpose: Genetic diagnosis of chromosomal abnormalities.
• Critical Limitation: CVS does NOT detect neural tube defects (NTDs).
• Method: Removal of a small tissue specimen from the fetal portion of the placenta.
• Risks:   - Bleeding, infection, and Rh sensitization.   - Limb Defects: Risk if the procedure is performed at $< 10$ weeks.

Vibroacoustic Stimulation (VST)

• Purpose: To stimulate the fetus during a Non-Stress Test (NST).
• Normal Result: Fetal heart rate acceleration follows stimulation.
• Abnormal Result: No response to stimulation, indicating the need for further testing.

Contraction Stress Test (CST) / Oxytocin Challenge Test

• Purpose: To identify a fetus that is compromised after the stress of a uterine contraction.
• Contraindications: Avoid in clients at risk with contractions, such as those with preterm labor, placental issues, uterine issues, or those unable to undergo vaginal birth.
• Method: Induce contractions through the administration of oxytocin or nipple stimulation.
• Interpretation of Results:   - Negative: No late decelerations (Normal).   - Positive: Repetitive late decelerations, specifically late decelerations with $\ge 50\%$ of contractions (Abnormal).   - Equivocal: Intermittent late decelerations.

Clinical Classification of Tests

• Tests to Determine Genetic Makeup:   - Maternal Serum Screening.   - Chorionic Villus Sampling (CVS).   - Amniocentesis.
• Tests to Assess Fetal Well-Being:   - Kick Counts.   - Non-Stress Test (NST).   - Biophysical Profile (BPP).   - Contraction Stress Test (CST).   - Ultrasound.   - Vibroacoustic Stimulation (VST).

Importance of Genetic Counseling

1. Explains the differences between screening tests and diagnostic tests.
2. Assists families in understanding potential risks.
3. Provides necessary emotional support.
4. Supports informed decision-making for the parents.
5. Discusses the risks of recurrence for specific conditions.

Risks Summary and Rh Administration

• Major Risks by Test:   - Amniocentesis: Miscarriage, infection, Rh sensitization.   - CVS: Miscarriage, limb defects if performed too early.   - CST: Preterm labor, uterine tachysystole.
• Rh Immune Globulin (RhoGAM) Requirements:   - Administer to Rh-negative mothers following:     - Amniocentesis.     - Chorionic Villus Sampling (CVS).     - Any invasive uterine procedure.     - Episodes of vaginal bleeding.

Final Assessment Summary Table

• Kick Counts: Normal is $\ge 10$ in $2$ hours; Abnormal is decreased counts.
• Non-Stress Test (NST): Normal is Reactive; Abnormal is Non-reactive.
• Contraction Stress Test (CST): Normal is Negative; Abnormal is Positive.
• Biophysical Profile (BPP): Normal is a score of $8 – 10$; Abnormal is a score of $\le 6$.
• Quad Screen: Normal is within range; Abnormal is a risk indicator only.
• Amniocentesis/CVS: Normal is a normal karyotype; Abnormal indicates a genetic abnormality.