Screening Tests in Pregnancy

Antenatal Screening - Bump's First Roadmap

Systematic tests during pregnancy to detect risks for mother and fetus, enabling timely interventions.

• Initial & Universal:
  • Blood group, Rh type, CBC, Hb electrophoresis
  • Infections: HIV, HBsAg, VDRL, Urine R/M & C/S
  • Rubella IgG, TSH
• Aneuploidy Screening:
  • Combined Test (First Trimester Screen): NT scan + PAPP-A + β-hCG
  • Quadruple Test (Second Trimester)
  • NIPT (cfDNA)
• Key Ultrasounds:
  • Early scan (dating)
  • NT scan (11-13+6 wks)
  • Anomaly scan (TIFFA: 18-22 wks)

⭐ In India, a single-step 75g OGTT is recommended for GDM screening at 24-28 weeks, or at first visit for high-risk women (as per DIPSI guidelines).

First Trimester Screening - Early Bird Detectives

• Timing: 11 - 13+6 weeks gestation.
• Combined Test Components:
  • Maternal Serum (Dual Test):
    • Free β-hCG: ↑ Trisomy 21; ↓ Trisomy 18/13.
    • PAPP-A (Pregnancy-Associated Plasma Protein-A): ↓ Trisomy 21, 18, 13.
  • Ultrasound (USG) Markers:
    • Nuchal Translucency (NT): ↑ suggests aneuploidy/cardiac defects. (Normal < 3.5 mm)
    • Nasal Bone (NB): Absent ↑ Trisomy 21 risk.
• Aims:
  • Screen for Trisomies 21, 18, 13.
  • Accurate dating (Crown-Rump Length - CRL).
  • Detect multiple pregnancies, major anomalies.
• Combined First Trimester Screening (CFTS):
  • Combines maternal age, NT, Free β-hCG, PAPP-A.
  • Trisomy 21 Detection Rate: ~90%; False Positive Rate: 5%.

  ⭐ PAPP-A levels are significantly decreased in Trisomies 21, 18, and 13, making it a crucial early marker.

Second Trimester Screening - Mid-Journey Checkpoint

• Optimal Timing:
  • Anomaly Scan (TIFFA/Level II): 18-20 weeks (acceptable up to 22 weeks).
  • Quadruple Test: 15-20 weeks (acceptable up to 22 weeks).
• Targeted Imaging for Fetal Anomalies (TIFFA) / Level II Scan:
  • Comprehensive fetal structural survey (e.g., brain, face, spine, heart, abdomen, limbs).
  • Assesses fetal biometry, placental localization, amniotic fluid volume (AFV).
  • Cervical length assessment.
  • 
• Quadruple Test (Serum Markers):
  • Components: Maternal serum AFP (Alpha-fetoprotein), hCG (Human Chorionic Gonadotropin), uE3 (Unconjugated Estriol), Inhibin A.
  • Screens for: Trisomy 21 (Down syndrome), Trisomy 18 (Edwards syndrome), Open Neural Tube Defects (ONTDs).
  • Trisomy 21: ↓AFP, ↓uE3, ↑hCG, ↑Inhibin A. (📌 Remember: HIgh hCG & Inhibin A)
  • Trisomy 18: ↓AFP, ↓uE3, ↓hCG (all significantly low).
  • Open NTDs: ↑↑AFP (significantly elevated, isolated finding).

⭐ Increased Nuchal Fold thickness (>6mm) on ultrasound is the most specific second-trimester soft marker for Down syndrome (Trisomy 21).

Late Pregnancy Screens - Homestretch Safeguards

• Gestational Diabetes (GDM):
  • Screen: 24-28 weeks.
  • India (DIPSI): 75g OGTT, 2-hr plasma glucose $\ge$ 140 mg/dL.
  • IADPSG: 75g OGTT; Fasting $\ge$ 92, 1-hr $\ge$ 180, 2-hr $\ge$ 153 mg/dL (any one).
• Group B Strep (GBS):
  • Screen: 36+0 to 37+6 weeks (rectovaginal swab).
  • Purpose: Intrapartum antibiotic prophylaxis (IAP) if positive.
• Anemia: Repeat Hb/Hct at 28-32 weeks.
• RhD Negative Mothers: Antibody screen at 28 weeks (before Anti-D Ig).
• Fetal Surveillance: As indicated (e.g., USG for growth, NST).

⭐ Universal GBS screening (rectovaginal swab) at 36+0 to 37+6 weeks significantly reduces early-onset neonatal GBS sepsis.

High‑Yield Points - ⚡ Biggest Takeaways

• Combined test (NT, β-hCG, PAPP-A) is optimal 1st-trimester aneuploidy screening.
• Quadruple test (AFP, β-hCG, uE3, Inhibin A) is key for 2nd-trimester screening (15-20 wks).
• NIPT (cell-free DNA) shows highest detection for trisomies 21, 18, 13.
• 75g OGTT is standard for GDM screening; DIPSI criteria (single step) widely used in India.
• Urine culture at first visit is crucial for detecting asymptomatic bacteriuria (ASB).
• Hb electrophoresis is vital for hemoglobinopathy screening (thalassemia, sickle cell).
• Universal screening for HIV, HBsAg, VDRL at the booking visit is mandatory.