Lab

Prenatal Lab

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Prenatal Lab, Antepartum Laboratory Testing

  • Labs
  • Initial - All Patients
  1. Complete Blood Count
    1. Hemoglobin
    2. Platelets
  2. Urine sample
    1. Urine Culture
    2. Urinalysis
      1. Asymptomatic Bacteriuria complicates 15% of pregnancies (Pyelonephritis develops in 30% of cases)
  3. Blood Type
    1. ABO and Rh
    2. Antibody screen (Coombs test)
  4. Rubella Antibody
    1. MMR contraindicated during pregnancy
    2. Administer postpartum MMR if negative
    3. Screen prior to pregnancy and immunize if negative
  5. Syphilis Serology
    1. Universal, first trimester Syphilis Screening recommended with automated Treponemal test
      1. Repeat testing at 28 weeks if at risk (e.g. STI history, exposures or high Prevalence region)
    2. Primary and secondary maternal Syphilis as well as Congenital Syphilis has increased significantly since 2015
      1. Untreated Syphilis is associated with adverse outcomes in up to 80% of affected pregnancies
        1. Tsai (2019) Obstet Gynecol Surv 74(9): 557-64 [PubMed]
      2. Half of patients asympomatic and without significant known risk factors
        1. Triveldi (2019) Obstet Gynecol 133(1): 27-32 [PubMed]
  6. Hepatitis B Surface Antigen (HBsAg)
    1. Universal screening recommended in U.S.
    2. If at risk, Hepatitis B Vaccine (safe in pregnancy)
  7. Hepatitis C Antibody
    1. ACOG recommends screening as part of Prenatal Labs
  8. HIV Test
    1. Universal screening recommended
    2. Consider HIV PrEP in patients at higher risk of STI
      1. HIV risk increases before, during and after pregnancy, esp. with history of Bacterial STI
      2. HIV PrEP with Truvada is considered safe in pregnancy (not in Lactation)
  9. Pelvic Exam Initial Labs
    1. Pap Smear
    2. Gonorrhea PCR and Chlamydia PCR
      1. Universal screening recommended
  10. Thyroid Stimulating Hormone (TSH, with reflex Free T4)
    1. See Pregnancy Risk Assessment regarding Thyroid disease risk in pregnancy
    2. See Thyroid Dysfunction in Pregnancy
    3. HIstorically has been a part of routine pregnancy labs in U.S.
      1. However no evidence that universal screening improves pregnancy outcomes
      2. Obtain if history of Thyroid disease or as clinical findings dictate
    4. References
      1. (2020) Obstet Gynecol 135(6):e261-74 +PMID: 32443080 [PubMed]
  • Labs
  • Initial - Specific Risk Factor Directed Tests
  1. Vaginitis testing if symptomatic
    1. Bacterial Vaginosis
    2. Trichomonas
    3. Genital Herpes
  2. Chlamydia and Gonorrhea PCR
    1. Indicated in maternal age <25 years or Sexually Transmitted Infection risk factors
    2. Repeat testing in third trimester if at risk
  3. Group B Streptococcus Culture
    1. Culture both vagina and anus
  4. Sickle Cell Anemia or Sickle Cell Trait screen
    1. Predisposes to Pyelonephritis
  5. Glucose Challenge Test (50 g Glucola drink)
  6. If no maternal history of Varicella infection
    1. Obtain varicella zoster IgG and if negative
      1. Avoid Varicella exposure
      2. If exposed, consider varicella Immunoglobulin
      3. Offer postpartum Varicella Vaccine
        1. Wait 3 months after last RhoGAM shot
    2. Varicella Vaccine is contraindicated in pregnancy
    3. Screen prior to pregnancy and immunize if negative
  • Labs
  • Second Trimester (16-18 weeks)
  1. See Triple Analyte Screen
  2. Consider first trimester screening of trisomy 16, 18
  3. Urine Culture
  • Labs
  • Early Third Trimester (26-28 weeks)
  1. Glucose Challenge Test (50 g Glucola drink)
  2. Hemoglobin
  3. If Rh Negative mother
    1. Repeat Antibody screen (Coombs test)
    2. Administer RhoGAM 300 mcg after blood draw
  4. If mother at risk for Sexually Transmitted Disease (e.g. age <25 years, incarceration, multiple sex partners, Illicit Drug use)
    1. Repeat RPR for Syphilis Testing
    2. Repeat Gonorrhea PCR and Chlamydia PCR
    3. Repeat Hepatitis B Surface Antigen (HBsAg)
    4. Repeat HIV Test
  5. If high risk for Preterm Labor
    1. Consider Bacterial Vaginosis screening
    2. Consider Fetal Fibronectin
  • Labs
  • Late Third Trimester (35-37 weeks)
  1. Group B Streptococcus screening
  • References
  1. Reese (2024) Am Fam Physician 109(1): 10-12 [PubMed]