224 lecture 2

Screening vs Diagnostic Testing

• Population-wide testing concept: when the same test is given to all people in a population, it is a screening test.

  • Example: at 12 years old, scoliosis screening is commonly performed for all.

  • In pregnancy, certain screenings are performed at specific gestational ages for everyone who is pregnant.

• Diagnostic testing is more definitive and specific: it answers yes/no about the condition.

  • Screening assesses risk; diagnostic testing confirms disease.

• Consent and patient preference:

  • Fetal diagnostic testing should be offered to patients who want to understand more about fetal conditions if congenital anomalies are present.

  • Diagnostic testing requires specific informed consent; not everyone wants a definitive diagnosis.

  • Example: high risk of Down syndrome on screening may lead some to pursue diagnostic testing, while others may choose not to know before birth.

• Nurse’s role:

  • Provide all information needed for informed decision-making.

  • Respect and support the patient’s chosen decision, regardless of personal beliefs.

Alpha-Fetoprotein (AFP) and Quad Screen

• AFP is a fetal protein that crosses the placenta into maternal circulation and reflects fetal development.

• Interpretation of maternal serum AFP:

  • Low AFP levels at given gestational age → higher risk of chromosomal abnormalities (e.g., monosomies, trisomies).

  • High AFP levels → higher risk of open neural tube defects or body wall defects (e.g., anencephaly, gastroschisis).

• Neural tube defects and related conditions:

  • Anencephaly: absence of a major portion of the brain; not compatible with life.

  • Spina bifida: a common neural tube defect.

  • Body wall defects: e.g., gastroschisis (intestines/liver outside the body).

• Screening timing and confounders:

  • Original AFP screening around $16-18$ weeks.

  • Confounding factors can skew results: gestational age inaccuracies, maternal weight/BMI, multifetal pregnancy, maternal diabetes, and race (e.g., African American) can affect accuracy.

  • False positives are common; AFP is a screening tool, not diagnostic.

• Counseling points:

  • AFP results reflect risk, not diagnosis.

  • Positive screening may lead to invasive diagnostic testing for confirmation.

• Examples used in lecture:

  • Maternal age $40$ with Down syndrome risk of about $rac{1}{8}$; AFP screening may reduce perceived risk to as low as $rac{1}{1000}$ or as high as $rac{1}{3}$ depending on results, guiding decisions about further testing.

• Quad screen (expanded screening): AFP remains one of the factors, but additional markers provide a better risk assessment.

  • Markers include:

  • Unconjugated estriol (uE3)

  • Human chorionic gonadotropin (hCG)

  • Inhibin-A

  • Combined interpretation improves risk estimation for chromosomal abnormalities and neural tube defects.

Ultrasound in Obstetrics

• What ultrasound does:

  • Uses sound waves to create images based on tissue density.

• Ultrasound flavors and equipment:

  • Two-dimensional (2D): standard black-and-white images.

  • Three-dimensional (3D) and Four-dimensional (4D): more detailed surface anatomy and real-time movement.

  • Doppler: evaluates blood flow (e.g., placenta, umbilical cord).

• First trimester ultrasound goals (transvaginal preferred):

  • Confirm pregnancy (viability).

  • Confirm intrauterine location (avoid ectopic pregnancy).

  • Determine gestational age accurately (within the first 12 weeks).

  • Detect multifetal pregnancy.

  • Screen for aneuploidy risk markers (nuchal translucency, nasal bone assessment).

  • Can guide diagnostic procedures (e.g., chorionic villus sampling, CVS).

• Second and third trimester ultrasound goals:

  • Confirm fetal viability and well-being.

  • Evaluate fetal anatomy (can be diagnostic if abnormalities are seen).

  • Estimate gestational age (less accurate later in pregnancy).

  • Serial fetal growth assessments (serial growth tracking).

  • Assess Doppler blood flow and placental status.

  • Locate and evaluate the placenta; assess placental position and potential placenta previa.

  • Determine fetal presentation and lie (Leopold’s maneuvers complement ultrasound).

  • Assess amniotic fluid volume (oligohydramnios vs. polyhydramnios).

  • Use biophysical profile (BPP) and specialized ultrasound for abnormal findings; involve pediatric cardiology if needed.

• Placenta and fluids:

  • Amniotic fluid is essential for protection, buoyancy, lung and organ development.

  • Oligohydramnios: too little fluid; polyhydramnios: too much fluid.

• Techniques for assessing cervix and anomalies:

  • Cervical incompetence may require transvaginal ultrasound to measure cervical length.

• Types of ultrasound views and details:

  • 2D: basic anatomy.

  • 3D/4D: detailed surface anatomy and motion.

  • Doppler: blood flow assessment; identify placental insufficiency or umbilical flow issues.

Non-Stress Test (NST)

• Purpose:

  • Assess fetal well-being in the absence of contractions (fetal stress test alternative).

• Eligibility:

  • Suitable for fetuses at least $24$ weeks gestation (viability threshold).

• Procedure:

  • Patient in semi-Fowler’s or left lateral tilt position.

  • Electronic fetal monitoring applied to the abdomen.

  • Transducer measures fetal heart rate; tocodometer measures uterine activity.

  • Noninvasive and immediate results.

• Interpretation:

  • Reactive NST: meets criteria (indicative of fetal well-being).

  • Nonreactive NST: does not meet criteria.

• Fetal heart rate basics:

  • Baseline HR: $110-160$ bpm (similar to newborn ranges).

  • Variability: moderate is desirable; limited discussion today.

  • Accelerations: transient increases in HR; expected with external stimuli or fetal movement.

  • In younger fetuses (< $32$ weeks), brain-heart coupling is weaker, accelerations may be smaller.

  • Decelerations: dips below baseline are concerning in NST.

• Quick interpretation example (lecture):

  • A fetal strip with a baseline around $115$ bpm and accelerations meeting 15 bpm above baseline for at least 15 seconds is reactive.

  • A flat line with no accelerations, e.g., baseline $110-115$ with no accelerations, is nonreactive.

• Advantages and limitations:

  • Advantages: noninvasive, quick, widely available, immediate results.

  • Limitations: high false-positive rate; baby may sleep and not show accelerations; efficacy affected by maternal obesity, multiple gestation, etc.

• Enhancement technique:

  • Vibroacoustic stimulation can wake sleeping fetuses to elicit accelerations.

Contraction Stress Test (CST)

• Purpose:

  • Assess fetal response to contractions by inducing uterine contractions (often via oxytocin).

• Outcome reporting:

  • Results are reportable as either negative or positive.

  • Negative CST: contractions occurred but no distress observed (fetal well-being maintained).

  • Positive CST: contractions associated with abnormal fetal heart rate patterns (concern for distress).

Biophysical Profile (BPP)

• What it is:

  • A five-part ultrasound-based scoring system; each component scores up to 2 points (total 0-10).

• Five components (brief overview):

  • Fetal heart rate (reactivity) baseline and variability factors.

  • Breathing movements.

  • Gross body movements.

  • Fetal tone (flexion/extension, posture).

  • Amniotic fluid volume.

• Interpretation (general guide, not memorized here):

  • 8-10: normal.

  • 4-6: concerning for fetal distress.

  • <4: severe fetal distress; immediate evaluation/decision for delivery may be indicated.

Invasive Diagnostic Tests and Related Procedures

• Amniocentesis (diagnostic):

  • Used in the second trimester to analyze fetal cells for chromosomal abnormalities; can also assess fetal lung maturity in the third trimester.

  • Counseling required; pregnancy loss