#47 – Obstetrical Screening


Initial Prenatal Visit

  • Aneuploidy
    • American College of Obstetrics and Gynecology (ACOG) recommends:
      • All women should be offered screening before 20 weeks
      • All women should have the option for having a more invasive procedure instead of screening regardless of maternal age
        • Amniocentesis
        • Chorionic villus sampling
    • Two major categories of screening available
      • Specific maternal serum biomarkers
        • Primarily trisomy 21 and 18
      • Maternal circulation cell-free DNA
        • More sensitive
        • Assesses trisomy 21, 18, 13, and sex chromosome aneuploidies
  • Carrier Screening
    • ACOG recommends:
      • All women should be offered carrier screening for cystic fibrosis, spinal muscular dystrophy, thalassemias, and hemoglobinopathies
      • Fragile X
        • All women with a family history of intellectual disability, developmental delay, or autism
      • Each provider develop a screening strategies for ethnic-specific and panethnic populations
    • If there is a (+) screening test in the mother, then the reproductive partner should be offered screening
  • Standard Panel Laboratory Screening
    • ABO and Rh Screen
      • RhD(-) women should receive prophylactic anti(D)-immune globin at 28-weeks
    • Complete Blood Count and RBC Indices
      • 1st Screen for anemia
    • Documentation of Rubella and Varicella Immunity
      • Rubella IgG
      • Varicella IgG
    • Urinalysis and Urine Culture
      • Urine Protein – establish baseline to compare if patient develops pre-eclampsia or eclampsia
      • Untreated, asymptomatic has higher rates of developing pyelonephritis, pre-term birth
    • HIV Screen
      • ACOG recommends “opt-out” approach
    • Hepatitis B
      • HBsAg regardless of immunization status
    • Chlamydia
      • Nucelic Acid Amplification Test (NAAT) of endocervical/vaginal swab or urine
    • Syphilis
      • Can screen with either a non-treponemal or treponemal test, but a (+) screening test is confirmed with a treponemal test
  • Selective Screening in 1st Trimester
    • Thyroid Function – TSH only
    • Overt diabetes screening
      • Obtain HgbA1C if BMI > 25 (23 in Asian Americans) AND at least one of the following:
        • Gestational diabetes in previous pregnancy
        • HgbA1C > 5.7%, impaired glucose tolerance, or impaired fasting glucose on previous testing
        • 1st degree relative with diabetes
        • African-American, Latino, Native American, Asian American, Pacific Islander
        • History of cardiovascular disease
        • Hypertension (> 140/90 or on medication)
        • Age > 40yr
        • HDL cholesterol < 35 mg/dL or triglyceride > 250 mg/dL
        • PCOS
        • Physical inactivity
        • Other insulin resistance conditions
      • If HgbA1C > 6.5%, then treat as overt diabetes
      • If HgbA1C (-), then screen again at 24-28 weeks
    • Infections
      • Gonorrhea
        • NAAT from endocervical/vaginal swab
      • Hepatitis C
        • High risk patient should be screened with anti-HCV antibody or HCV RNA
      • Tuberculosis
        • Screen with tuberculin skin test or interferon-gamma release assay (IGRA) only if:
          • Suspicion for recent TB infection
          • Immunocompromised
      • Others
        • Toxoplasmosis, trichomonas, herpes simplex, cytomegalovirus, Zika, and Chagas are available for at risk patients or in endemic regions
    • Lead
      • Women with symptoms of lead exposure or risk factors

15-24 Weeks

  • These are not universal and are options available to mothers
  • Quadruple Test
    • Maternal serum alpha-fetoprotein level
    • Unconjugated estriol
    • Human chorionic gonadotropin
    • Inhibin A
  • Fetal ultrasound
    • Can be used to screen for neural tube defects and other fetal anomalies, as well as screen the mother for a short cervical length (< 25mm) that can increased her risk of spontaneous preterm birth

24-28 Weeks

  • Gestational Diabetes Screening
    • Two-Step Approach
      • Step One – Screening
        • 50g, one-hour glucose challenge test REGARDLESS of time of day or last meal
      • Step Two – Diagnostic
        • 100g, three-hour oral glucose tolerance test
          • Traditionally diagnostic after 2 elevated values, but newer data suggests that one may be OK
        • 75g, two-hour oral glucose tolerance test
          • Diagnostic after a single elevated value, but patient must be fasting
  • Complete Blood Count with iron and folate studies
    • 2nd anemia screening

28-36 Weeks

  • Sexually Transmitted Infection Screening
    • HIV, syphilis, chlamydia, gonorrhea, hepatitis B and C
    • Based on either previous (+) result or evidence of risk factors
  • Screen for group B beta-hemolytic streptococcus
    • Vaginal and rectal swabs
    • (+) results treated with intrapartum prophylaxis
CDC – GBS Prophylactic Antibiotic Algorithm
  • Screen for Fetal Growth Restrictions (<10th percentile weight for gestational age)
    • Indicated in third trimester in pregnancies at high risk
      • Infections, fetal anomalies, preeclampsia, gestational HTN and DM, alcohol use, placental/cord abnormalities


  1. ACOG Practice Bulletin No. 77: screening for fetal chromosomal abnormalities. Obstetrics and gynecology. 2007; 109(1):217-27. [pubmed]
  2. ACOG Practice Bulletin No. 88, December 2007. Invasive prenatal testing for aneuploidy. Obstetrics and gynecology. 2007; 110(6):1459-67. [pubmed]
  3. ACOG Committee Opinion No. 752: Prenatal and Perinatal Human Immunodeficiency Virus Testing. Obstetrics and gynecology. 2018; 132(3):e138-e142. [pubmed]
  4. Roberts SW, Sheffield JS, McIntire DD, Alexander JM. Urine screening for Chlamydia trachomatis during pregnancy. Obstetrics and gynecology. 2011; 117(4):883-5. [pubmed]
  5. Hughes BL, Page CM, Kuller JA. Hepatitis C in pregnancy: screening, treatment, and management. American journal of obstetrics and gynecology. 2017; 217(5):B2-B12. [pubmed]
  6. ACOG Practice Bulletin No. 190: Gestational Diabetes Mellitus. Obstetrics and gynecology. 2018; 131(2):e49-e64. [pubmed]
  7. Centers for Disease Control.  Group B Strep (GBS).  https://www.cdc.gov/groupbstrep/guidelines/new-differences.html
  8. Bricker L, Medley N, Pratt JJ. Routine ultrasound in late pregnancy (after 24 weeks’ gestation). The Cochrane database of systematic reviews. 2015; [pubmed]

One thought on “#47 – Obstetrical Screening

  1. Pingback: #70 – Newborn Examination | PAINE Podcast and Medical Blog

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