What labs are recommended for a 1st trimester pregnancy?

Recommended Laboratory Tests for First Trimester Pregnancy

All pregnant women in the first trimester should have the following laboratory tests: complete blood count, blood type and Rh status, serologic tests for syphilis, hepatitis B surface antigen, HIV, and a screening test for aneuploidy. 1, 2

Essential First Trimester Laboratory Tests

Blood Tests

• Complete blood count (CBC) - To screen for anemia; hemoglobin <11.0 g/dL in first trimester indicates anemia 3
• Blood type and Rh status - To identify Rh-negative women who will need Rh immune globulin at 28 weeks 2
• Serologic test for syphilis - All women should be screened early in pregnancy 1
• Hepatitis B surface antigen (HBsAg) - Essential for preventing mother-to-child transmission 1
• HIV test - Recommended for all pregnant women, with appropriate counseling and informed consent 1

Genetic Screening

• First trimester combined screening (11-13+6 weeks) - Includes:
  • Nuchal translucency (NT) measurement
  • PAPP-A (pregnancy-associated plasma protein A)
  • hCG or free beta-hCG 1, 2

Additional Recommended Tests

Infectious Disease Screening

• Rubella immunity - To identify susceptible women 4
• Chlamydia trachomatis - For women <25 years or with new/multiple partners 1
• Hepatitis C antibody - For women with risk factors 1

Metabolic/Nutritional Tests

• Serum ferritin - When anemia is detected to confirm iron deficiency (diagnostic if <30 ng/mL) 5
• Thyroid function tests - TSH screening recommended in first trimester 4

Special Considerations

Aneuploidy Screening Options

1. First trimester combined screening - Detects 75-80% of trisomy cases with 5% false-positive rate 1
2. Cell-free DNA screening - Can be performed after 10 weeks with higher sensitivity for common trisomies 2
3. Integrated screening - Combines first and second trimester markers for higher detection rates 1

Diagnostic Testing Options

• Chorionic villus sampling (CVS) - Available from 10-13 weeks for definitive diagnosis 1
• Amniocentesis - Available after 15 weeks for definitive diagnosis 1, 2

Important Considerations

• Dating accuracy is critical for proper interpretation of screening tests. First trimester ultrasound with crown-rump length ≥10mm is most accurate (±7 days) 2
• Maternal weight, race, diabetes status, and multiple gestation can affect screening results 2
• Screening cutoffs should be based on patient-specific risk rather than maternal age alone 1
• Increased NT measurement (≥3.5 mm) warrants detailed anatomic ultrasound and echocardiogram even with normal karyotype 1

Common Pitfalls to Avoid

• Relying solely on LMP for dating - Can lead to inaccurate screening results due to recall bias or irregular cycles 2
• Missing hepatitis B screening - Essential for preventing vertical transmission through appropriate neonatal prophylaxis 1
• Overlooking anemia screening - Iron deficiency anemia is the most common hematologic abnormality in pregnancy and is associated with adverse outcomes 3
• Failing to offer genetic screening options - All women should be offered screening regardless of age 1

By implementing this comprehensive first trimester laboratory screening protocol, providers can identify and address potential complications early, improving outcomes for both mother and baby.