What are the American College of Obstetricians and Gynecologists (ACOG) guidelines for perinatal testing, labs, screening, and imaging in the first, second, and third trimesters?

ACOG Guidelines for Perinatal Testing, Labs, Screening, and Imaging by Trimester

The American College of Obstetricians and Gynecologists (ACOG) recommends comprehensive perinatal testing throughout pregnancy with specific protocols for each trimester, including universal screening for genetic disorders, infections, and anatomical abnormalities.

First Trimester (0-13 weeks)

Laboratory Testing

• Blood type and Rh status - Required at first prenatal visit 1
• Complete blood count (CBC) - Screen for anemia 1
• Infectious disease screening:
  • Hepatitis B surface antigen (HBsAg) 1
  • HIV testing 1
  • Syphilis serology 1
  • Hepatitis C screening for women at risk per CDC guidelines 1

Genetic Screening

• Aneuploidy screening options (offer to all pregnant women regardless of age or risk factors):
  • First trimester combined screening (11-13+6 weeks) including:
    • Nuchal translucency (NT) measurement
    • Pregnancy-associated plasma protein A (PAPP-A)
    • Human chorionic gonadotropin (hCG) or free beta-hCG
    • Detection rate: 75-80% for trisomy 21 with 5% false-positive rate 1
  • Cell-free DNA screening (can be performed anytime after 10 weeks) 1

Diagnostic Testing

• Chorionic villus sampling (CVS) - Available from 10-13 weeks for definitive diagnosis 1
• Should be offered to women 35 years and older and those with positive screening tests 1

Ultrasound

• Dating ultrasound with crown-rump length measurement (accuracy within ±7 days) 1
• Nuchal translucency assessment at 11-14 weeks 2
  • Increased NT defined as ≥3 mm or above 99th percentile for crown-rump length 2
  • Should not be used in isolation (detects only 70% of trisomy 21 fetuses) 2
  • Transvaginal approach may be needed in 5% of patients when transabdominal imaging is inadequate 2

Risk Assessment

• Preeclampsia risk assessment in first trimester 1
  • Women at high risk should receive aspirin prophylaxis before 16 weeks' gestation 1
• Multiple gestation assessment - Critical to establish chorionicity and amnionicity 1

Second Trimester (14-27 weeks)

Laboratory Testing

• Gestational diabetes screening after 24 weeks 1
  • 50-g oral glucose challenge test (OGCT) with cutoff value of 130-140 mg/dL
  • If abnormal, follow with 100-g 3-hour oral glucose tolerance test

Genetic Screening

• Quadruple screening (15-20 weeks) if not done in first trimester 1
• Integrated screening combining first and second trimester markers 1

Diagnostic Testing

• Amniocentesis - Available after 15 weeks for definitive diagnosis 1, 3

Ultrasound

• Standard anatomy scan at 18-20 weeks 2
  • Components outlined in ACR-ACOG-AIUM-SMFM-SRU Practice Parameter
  • For obese patients, consider anatomy scan at 20-22 weeks with follow-up in 2-4 weeks if incomplete 2

Soft Marker Evaluation

• Isolated soft markers found during anatomy scan require specific follow-up 2:
  • Echogenic intracardiac focus - No further evaluation if negative screening 2
  • Echogenic bowel - Evaluate for cystic fibrosis and CMV infection; third-trimester growth scan 2
  • Choroid plexus cysts - No further evaluation if negative screening 2
  • Single umbilical artery - Third-trimester growth scan; consider weekly antenatal surveillance from 36 weeks 2
  • Urinary tract dilation - Follow-up ultrasound at 32 weeks 2
  • Shortened humerus/femur - Third-trimester reassessment and growth evaluation 2
  • Thickened nuchal fold/absent nasal bone - Consider additional aneuploidy evaluation 2

Third Trimester (28-40+ weeks)

Laboratory Testing

• Repeat CBC if indicated by earlier results
• Group B Streptococcus (GBS) screening at 36-37 weeks

Ultrasound

• Follow-up ultrasound for patients with:
  • Abnormal second-trimester findings
  • Fetal growth concerns
  • Placental issues
  • Amniotic fluid abnormalities

Antepartum Fetal Surveillance

• Indicated for high-risk conditions 4:
  • Maternal medical conditions (diabetes, hypertension)
  • Pregnancy complications (FGR, preeclampsia)
  • Decreased fetal movement
  • Post-term pregnancy
  • Multiple gestation with complications
  • Prior stillbirth
• Testing modalities:
  • Non-stress test (NST)
  • Biophysical profile (BPP)
  • Modified BPP (NST plus amniotic fluid assessment)
  • Contraction stress test (CST)
  • Doppler velocimetry in growth restriction

Special Considerations

Multiple Gestations

• Require more frequent ultrasound examinations than singleton pregnancies 1
• Twin-specific screening protocols including:
  • More frequent growth assessments
  • Screening for twin-to-twin transfusion syndrome in monochorionic twins 1

Maternal Age ≥35 Years

• Offer diagnostic testing (CVS or amniocentesis) in addition to screening options 3

Fetal Anomalies

• When major anomalies are found, follow-up should include 2:
  • Detailed ultrasound scan
  • Fetal MRI without IV contrast when indicated
  • Fetal echocardiography when indicated
  • Serial follow-up ultrasounds

Implementation Considerations

• Implementing full ACOG antepartum testing recommendations may increase testing volume by approximately 23% compared to more limited protocols 5
• Perinatal depression screening should be performed at least once during pregnancy and at the comprehensive postpartum visit using a standardized, validated tool 6

Note: These guidelines represent standard recommendations but may need to be adjusted based on specific risk factors and clinical circumstances.