What is included in routine prenatal lab work?

Routine Prenatal Laboratory Work

Routine prenatal laboratory work should include blood type and Rh factor, complete blood count, screening for infections, genetic screening, and urinalysis to identify potential risks to maternal and fetal health.

First Trimester Laboratory Tests

• Blood type and Rh factor testing to identify women who are Rh-negative and may require Rh immunoglobulin at 29 weeks gestation and after delivery 1
• Complete blood count (CBC) to assess for anemia and other hematologic abnormalities 2
• Antibody screening to identify women with alloantibodies that could cause hemolytic disease of the fetus and newborn 1
• Screening for infections including:
  • Hepatitis B surface antigen
  • HIV testing
  • Syphilis screening
  • Rubella immunity status 2
• Urinalysis and urine culture to screen for asymptomatic bacteriuria 2
• Genetic screening options including:
  • First trimester screening for chromosomal abnormalities (11-13 weeks) which may include:
    • PAPP-A (pregnancy-associated plasma protein A)
    • Free beta-hCG or total hCG
    • Nuchal translucency (NT) measurement via ultrasound 3
  • Cell-free fetal DNA screening (can be performed as early as 9 weeks) 2

Second Trimester Laboratory Tests

• Maternal serum screening for chromosomal abnormalities (15-20 weeks) which typically includes:
  • Alpha-fetoprotein (AFP) for neural tube defect screening 3
  • hCG (human chorionic gonadotropin)
  • Unconjugated estriol (uE3)
  • Inhibin A 3
• Screening for gestational diabetes (24-28 weeks) 2
• Additional screening for anemia if indicated 2
• Group B streptococcus screening (35-37 weeks) 2

Special Considerations for High-Risk Pregnancies

• Early diabetes screening for women with risk factors for pre-existing diabetes 2
• Serial monitoring of antibody titers for women with alloimmunization 1
• Additional ultrasound assessments for fetal growth and well-being 4
• Doppler ultrasound of umbilical and fetal middle cerebral arteries in cases of growth restriction 2

Quality Control in Prenatal Laboratory Testing

• Laboratories must establish their own normative data for screening tests rather than using package insert (commercial) medians 3
• Regular monitoring of median values for analytes used in screening tests 3
• Participation in external proficiency testing programs 3
• Proper documentation of in-house validation of test methodologies 3

Common Pitfalls to Avoid

• Failure to adjust screening test results for maternal weight, which can affect interpretation 3
• Incorrect dating of pregnancy leading to misinterpretation of screening results 3
• Reclassification of screen-positive results to screen-negative should only be considered when revised gestational age estimates differ by at least a week 3
• Lack of follow-up for screen-positive results, which should be promptly communicated to healthcare providers 3
• Not recognizing that elevated AFP levels, even in the absence of neural tube defects, may be associated with poor pregnancy outcomes 3

Reporting Requirements

Laboratory reports for prenatal screening should include:

• Patient identifiers
• Referring physician information
• Test ordered
• Specimen type
• Collection date
• Demographic and pregnancy-related information used in interpretation
• Analytic results in both mass units and interpretive units
• Clear clinical interpretation 3