Overview
This lecture covers prenatal screening and fetal testing methods used during pregnancy to evaluate maternal and fetal health, focusing on indications, procedures, and interpretation of results.
Ultrasound in Pregnancy
- Ultrasound confirms intrauterine pregnancy and excludes ectopic or molar pregnancies in the first trimester.
- Used to determine gestational age by measuring crown-rump length (CRL), most accurate between 7-10 weeks.
- Assesses singleton vs. multiple gestations.
- In the third trimester, evaluates fetal well-being, position, biophysical profile, water status (oligohydramnios, polyhydramnios), and fetal anemia with transcranial Doppler (>20 weeks).
- Ultrasound is non-invasive and safe for both mother and fetus.
Fetal Heart Monitoring Tests
- Non-Stress Test (NST): Monitors fetal heart rate accelerations (2 increases of ≥15 bpm for ≥15 sec in 20 min; "15 for 15" rule; baseline 110-160 bpm; moderate variability required; no late or variable decelerations).
- Contraction Stress Test (CST): Assesses fetal response to induced contractions (≥3 contractions in 10 min, ≥200 Montevideo units); monitors for bradycardia and decelerations.
- Early decelerations: mirror contractions, benign.
- Variable decelerations: V-shaped, suggest cord compression, concerning if recurrent.
- Late decelerations: begin after contraction peak, indicate placental insufficiency, require immediate delivery.
Biophysical Profile (BPP)
- Combines NST with ultrasound assessment of breathing, movements, muscle tone, and amniotic fluid (2 points each, max 10).
- Scores: 8-10 normal, 6 equivocal, <4 abnormal (indication for delivery).
Diabetes Screening
- Screen for gestational diabetes after 20 weeks using 1-hour glucose tolerance test (50g glucose; >140 mg/dL proceed to 3-hour test).
- Diagnosis if any values are elevated at 0, 1, 2, or 3 hours in 3-hour test.
- Initial management: diet/exercise; add insulin or metformin if needed.
Rh Alloimmunization Screening
- Screen if mother is Rh-negative; check for antibodies.
- Rh-negative mothers with Rh-positive or unknown fathers receive RhoGAM at 28 weeks and delivery.
- Use transcranial Doppler for fetal anemia if maternal antibodies are present.
Anemia Screening in Pregnancy
- Physiological anemia is expected due to plasma volume increase; hemoglobin should not drop below 10 g/dL at 28 weeks.
- Screen at 20 weeks with CBC; low levels require iron studies; iron deficiency is most common, treated with supplements.
Invasive Diagnostic Tests
- Amniocentesis: Transabdominal sampling of amniotic fluid after 16 weeks, for genetic and neural tube defect testing; small risk of complications; now often replaced by quad screen or cell-free DNA.
- Chorionic Villus Sampling (CVS): Performed at ≥10 weeks for early genetic diagnosis; 1 in 500 risk of fetal loss.
- Percutaneous Umbilical Blood Sampling (PUBS): Sampling umbilical vein blood after 18-20 weeks for fetal anemia, infection, or genetic defects; creates vascular access for possible transfusion.
Key Terms & Definitions
- Ultrasound — Imaging using sound waves to visualize fetus and structures.
- Crown-Rump Length (CRL) — Measurement from fetal head to buttock to estimate gestational age.
- Non-Stress Test (NST) — Fetal heart rate monitoring without contractions.
- Contraction Stress Test (CST) — Fetal heart monitoring during induced contractions.
- Biophysical Profile (BPP) — Combined fetal assessment scoring system.
- Gestational Diabetes — Diabetes diagnosed during pregnancy after 20 weeks.
- Rh Alloimmunization — Maternal immune response to fetal Rh antigen.
- Amniocentesis — Amniotic fluid sampling for prenatal diagnosis.
- Chorionic Villus Sampling (CVS) — Early placental tissue sampling for genetic analysis.
- Percutaneous Umbilical Blood Sampling (PUBS) — Direct umbilical blood sampling for fetal testing.
Action Items / Next Steps
- Review maternal and fetal monitoring protocols.
- Study interpretation criteria for NST, CST, and BPP.
- Prepare for practice questions on prenatal screening indications and results.
- Read assigned textbook chapters on prenatal diagnostic procedures.