What prenatal labs are recommended during pregnancy?

Recommended Prenatal Laboratory Testing

All pregnant women should be screened at the first prenatal visit for hepatitis B surface antigen (HBsAg), HIV, syphilis, chlamydia, and gonorrhea, with additional testing for rubella immunity and blood type/antibody screen. 1, 2

First Prenatal Visit - Universal Screening Panel

Infectious Disease Screening (Required for All)

• Hepatitis B surface antigen (HBsAg) - Screen during first trimester even if previously vaccinated or tested 1, 3
• HIV antibody testing - Use opt-out approach where women are notified testing is recommended but can decline 1, 4
• Syphilis serology - Both treponemal and non-treponemal testing required 1, 2, 5
• Rubella antibody status - Identify susceptible women for postpartum vaccination 6, 7

STI Screening Based on Risk

• Chlamydia and gonorrhea - Screen all pregnant women under age 25 or those at increased risk (multiple partners, new partner, inconsistent condom use, history of STIs) 1, 2
• Hepatitis C antibody - Test women with history of injection drug use or blood transfusion/organ transplant before 1992 1

Additional Standard Tests

• Blood type and antibody screen - Identify Rh status and irregular antibodies 6
• Complete blood count - Assess for anemia 6

Third Trimester Screening

High-Risk Populations Requiring Repeat Testing

• Repeat HIV testing before 36 weeks for women at high risk (injection drug use, multiple partners, incarcerated, areas with HIV incidence ≥1 per 1,000 pregnant women per year) 1, 4
• Repeat syphilis testing at 28 weeks and at delivery for women at high risk, living in areas of high syphilis morbidity, or previously untested 1, 2, 5
• Repeat HBsAg at delivery for women engaging in high-risk behaviors (injection drug use, >1 sex partner in previous 6 months, HBsAg-positive partner, recent STD treatment) 1

Universal Third Trimester Testing

• Group B streptococcus (GBS) screening at 35-37 weeks - Vaginal-rectal swab culture 6
• Gestational diabetes screening - Typically performed 24-28 weeks 6

Labor and Delivery - Unknown Status

For women with unknown HIV status at delivery, perform rapid HIV testing immediately using opt-out approach, with results available within 1 hour 1, 4

• If rapid HIV test is reactive, initiate antiretroviral prophylaxis immediately without waiting for confirmatory results 1
• Test for HBsAg at hospital admission if prenatal status unknown 1
• Any woman delivering a stillborn infant should be tested for syphilis 1

Critical Management Points

Hepatitis B Positive Mothers

• Infants must receive hepatitis B vaccine and hepatitis B immune globulin (HBIG) within 12 hours of birth 1
• Check HBV DNA levels - if ≥200,000 IU/mL, initiate tenofovir (TDF) at 28-32 weeks gestation to reduce transmission risk 1
• Earlier antiviral initiation (before 28 weeks) if HBV DNA ≥7 log IU/mL 1

HIV Positive Mothers

• Immediate linkage to HIV specialist for antiretroviral therapy 1, 4
• Antiretroviral prophylaxis reduces perinatal transmission from 25% to <2% 1

Syphilis Positive Mothers

• Treat with appropriate penicillin regimen for disease stage >4 weeks before delivery for optimal outcomes 5
• Consider additional benzathine penicillin G 2.4 million units IM one week after initial dose for primary/secondary/early latent syphilis in pregnancy 5

Common Pitfalls to Avoid

• Do not skip third trimester repeat testing in high-risk women - this identifies new infections acquired during pregnancy that require immediate intervention 1, 2
• Do not delay infant immunoprophylaxis - hepatitis B vaccine and HBIG must be given within 12 hours of birth for HBsAg-positive mothers 1
• Do not rely on risk-based HIV screening alone - universal opt-out screening identifies more infected women than targeted testing 1
• Do not forget postpartum rubella vaccination for susceptible women - only 65.7% receive recommended vaccination 7
• Do not use single syphilis test - diagnosis requires both treponemal and non-treponemal results 5

Inadequate Prenatal Care

Women with inadequate prenatal care have 14.6 times higher risk of missing recommended screening tests 7. Black women are disproportionately affected, with lower rates of adequate prenatal care and higher rates of HBsAg and syphilis positivity, yet lower rates of receiving prevention interventions 7.