What are common prenatal and perinatal tests, procedures, and imaging?

Common Prenatal and Perinatal Testing, Procedures, and Imaging

Transabdominal and transvaginal ultrasound are the cornerstone of prenatal evaluation, with specific timing and indications for additional testing such as fetal echocardiography, Doppler studies, and genetic testing based on risk factors and gestational age. 1

First Trimester Testing (Weeks 1-13)

Ultrasound

• Transabdominal and transvaginal ultrasound (10-14 weeks)
  • Confirms pregnancy location, viability, and dating
  • Evaluates for multiple gestations and determines chorionicity/amnionicity
  • Measures nuchal translucency (NT) at 11-13+6 weeks 1, 2
  • Documents embryonic/fetal cardiac activity

Genetic Screening

• First trimester combined screening (11-13+6 weeks)
  • NT measurement plus maternal serum PAPP-A and free β-hCG
  • Detection rate ~85% for Down syndrome with 5% false-positive rate 2
• Cell-free DNA (cfDNA) screening
  • 99% detection rate for trisomy 21 with 1-9% screen positive rate
  • Typically performed after 10 weeks 2

Diagnostic Testing

• Chorionic villus sampling (CVS) (10-13 weeks)
  • Invasive diagnostic test for chromosomal abnormalities
  • Indicated for advanced maternal age, abnormal screening, family history 2, 3

Second Trimester Testing (Weeks 14-27)

Ultrasound

• Anatomy scan (18-22 weeks)
  • Standard of care for all pregnancies 1
  • Evaluates fetal anatomy, growth, amniotic fluid, and placenta
  • May be performed 2 weeks later (20-22 weeks) in obese patients 1
• Cervical length measurement (transvaginal)
  • Screens for risk of preterm birth
  • Particularly important in multiple gestations 1

Diagnostic Testing

• Amniocentesis (15-20 weeks)
  • Invasive diagnostic test for chromosomal and genetic disorders
  • Indicated for advanced maternal age, abnormal screening, family history 2, 3

Specialized Testing

• Fetal echocardiography (18-22 weeks)
  • Detailed evaluation of fetal cardiac structures
  • Indicated for maternal diabetes, family history of congenital heart disease, abnormal anatomy scan, multiple gestations (especially monochorionic) 1
• Glucose tolerance test (24-28 weeks)
  • Screens for gestational diabetes 2

Third Trimester Testing (Weeks 28-40)

Growth Assessment

• Serial growth ultrasounds (every 3-4 weeks from 28-32 weeks)
  • Monitors fetal growth
  • Particularly important in high-risk pregnancies (advanced maternal age, multiple gestations, suspected growth restriction) 1, 2

Fetal Well-Being Assessment

• Biophysical Profile (BPP)
  • Evaluates four ultrasound components: fetal breathing movements, body movements, tone, and amniotic fluid volume
  • Score of 8-10 is normal, 6 is equivocal, 4 or less is abnormal 1
• Modified BPP
  • Combines amniotic fluid assessment with non-stress test (NST) 1
• Non-stress test (NST)
  • Records fetal heart rate response to movement
  • Typically begins at 32-34 weeks in high-risk pregnancies 1, 2

Doppler Studies

• Umbilical artery Doppler
  • Evaluates placental function
  • Indicated for suspected fetal growth restriction (FGR) 1
• Middle cerebral artery Doppler
  • Assesses fetal brain blood flow
  • Used in FGR, multiple gestations (especially monochorionic) 1
• Ductus venosus Doppler
  • Evaluates fetal cardiac function
  • Abnormal flow associated with poor outcomes in FGR 1

Special Considerations for Multiple Gestations

• First trimester: Early determination of chorionicity and amnionicity is critical 1
• Second trimester: Document placental cord insertion for each fetus, especially in monochorionic pregnancies 1
• Third trimester: More frequent monitoring with growth scans every 3-4 weeks 1
• Monochorionic twins: Additional surveillance for twin-twin transfusion syndrome (TTTS) starting at 16 weeks 1

Advanced Imaging Techniques

• 3D/4D ultrasound
  • Helpful for evaluating facial anomalies (clefts) 1
• Fetal MRI (without contrast)
  • Complementary to ultrasound for evaluating complex anomalies
  • Not used for routine screening
  • Particularly useful for CNS, thoracic, and abdominal anomalies 4, 5, 6

Common Pitfalls and Caveats

• Timing is critical: Chorionicity determination is most accurate in the first trimester 1
• Obesity affects imaging: Consider delayed anatomy scan (20-22 weeks) and transvaginal approach in obese patients 1
• Growth discordance: In multiple gestations, document and monitor closely as it may indicate complications 1
• False positives: Antenatal testing in low-risk women can lead to iatrogenic prematurity 1
• Limitations of ultrasound: Some skeletal dysplasias may not be detectable until later in pregnancy or even after birth 1

Remember that while these tests and procedures represent standard practice, the frequency and timing should be adjusted based on specific risk factors and findings throughout pregnancy.