What are the pregnancy screenings by gestational age?

Comprehensive Pregnancy Screening Schedule by Gestational Age

All pregnant women should undergo a systematic series of screenings throughout pregnancy, with specific tests performed at optimal gestational ages to maximize detection of fetal abnormalities and maternal complications.

First Trimester (Weeks 1-13)

Weeks 8-10

• Initial prenatal visit with complete medical history and physical examination
• Blood type and Rh factor
• Complete blood count (CBC)
• Rubella immunity
• Hepatitis B surface antigen
• HIV testing
• Syphilis screening
• Urine culture for asymptomatic bacteriuria
• Chlamydia and gonorrhea testing for at-risk women

Weeks 11-13

• First trimester aneuploidy screening 1:

  • Nuchal translucency (NT) ultrasound measurement
  • Maternal serum pregnancy-associated plasma protein A (PAPP-A)
  • Free beta-hCG or total/intact hCG
  • Optimal timing is 11 completed weeks for best sensitivity and specificity 2
  • Clinical sensitivity decreases by 13 completed weeks' gestation

• First trimester ultrasound for:

  • Dating (crown-rump length measurement)
  • Viability assessment
  • Determination of chorionicity in multiple gestations 1
  • Limited structural survey (major abnormalities of fetal head, abdominal wall, and urinary tract may be detected) 3

Second Trimester (Weeks 14-27)

Weeks 15-20

• Maternal serum AFP screening for open neural tube defects (ONTDs) 1:
  • Optimal timing is 16-18 weeks' gestation
  • Adjustments made for maternal weight, race, and insulin-dependent diabetes mellitus
  • Multiple marker screening (quad screen) includes:
    • Alpha-fetoprotein (AFP)
    • Human chorionic gonadotropin (hCG)
    • Unconjugated estriol (uE3)
    • Inhibin-A

Weeks 18-22

• Comprehensive fetal anatomy ultrasound 1:
  • Detailed assessment of fetal anatomy
  • Placental location and appearance
  • Amniotic fluid assessment
  • Cervical length measurement
  • Fetal echocardiography if indicated

Weeks 24-28

• Gestational diabetes screening 1, 4:
  • 50-g oral glucose challenge test (OGCT)
  • If abnormal (>130-140 mg/dL), followed by 100-g 3-hour oral glucose tolerance test
  • Two or more abnormal values on OGTT confirm gestational diabetes diagnosis
• Complete blood count (CBC) to screen for anemia
• Antibody screening for Rh-negative women
• Administration of Rh immunoglobulin if indicated

Third Trimester (Weeks 28-40)

Weeks 28-32

• Assessment of fetal growth and well-being
• Repeat antibody screening for Rh-negative women who received Rh immunoglobulin

Weeks 35-37

• Group B streptococcus (GBS) screening
• Assessment of fetal presentation
• Discussion of labor signs and delivery planning

Special Considerations

Integrated/Sequential Screening Options

• Serum integrated screening 1:

  • PAPP-A in first trimester (optimal at 10 weeks)
  • Quad screen in second trimester (15-20 weeks)
  • Single risk assessment reported in second trimester
  • Detection rate ~89% for Down syndrome

• Full integrated screening 1:

  • NT plus PAPP-A in first trimester
  • Quad screen in second trimester
  • Single risk assessment reported in second trimester
  • Detection rate ~92% for Down syndrome

• Sequential screening 1:

  • First trimester results reported (NT, PAPP-A, hCG)
  • High-risk patients offered CVS
  • Lower-risk patients proceed to second trimester screening
  • Final risk assessment incorporating both trimesters

Non-Invasive Prenatal Testing (NIPT)

• Cell-free DNA screening 1:
  • Can be performed anytime during pregnancy after 10 weeks
  • Superior sensitivity for detecting common trisomies (13,18, and 21)
  • Should be made available to all pregnant patients regardless of risk status
  • No ultrasound required for testing

Multiple Gestations

• More frequent monitoring of fetal growth
• Twin-specific screening protocols for aneuploidy
• Assessment for twin-specific complications:
  • For monochorionic twins: Twin-to-twin transfusion syndrome (TTTS) screening 1
  • For all twins: More frequent growth assessments

Important Considerations for Screening

• Gestational age accuracy is critical for proper interpretation of screening results 2

• Crown-rump length provides the most accurate dating in first trimester (within 7 days)

• Maternal factors affecting screening markers include:

  • Weight (heavier women have lower serum marker levels)
  • Race (Black/African American women have 10-15% higher AFP levels)
  • Insulin-dependent diabetes (10-20% lower AFP levels)

• Two-stage screening (first and second trimester combined) shows higher detection rates (83.8%) compared to single-stage second trimester screening (50.5%) for structural anomalies 5