Objectives

Case snapshot (de-identified)

Maternal
  • 33-year-old, G3P2
  • Class III obesity (BMI ~42)
  • Prior cesarean, then successful VBAC
  • Normotensive at visit
Ultrasound (18+ weeks)
  • EFW appropriate; normal FHR
  • Normal fluid by MVP method
  • Cervical length normal
  • Anatomy suboptimal; placental edge “circumvallate” suspected

Why class III obesity matters

Maternal
  • Gestational diabetes
  • Hypertensive disorders
  • Cesarean & wound morbidity
Fetal
  • Congenital anomaly detection limits
  • Stillbirth risk rises with BMI
  • Growth abnormalities
Systems
  • Anesthesia/airway planning
  • Hemorrhage preparedness
  • VTE risk management

Screening & prevention (obesity)

DomainCommon approach
Diabetes Assess for early screening if additional risk factors; routine 24–28 week screening.
Preeclampsia prevention Low-dose aspirin if criteria met (obesity is a moderate-risk factor; usually needs ≥2 moderate-risk factors).
Anatomic evaluation Detailed anatomy often indicated; repeat scan if incomplete visualization.

Apply individualized risk criteria; avoid “one-size-fits-all” prophylaxis.

Ultrasound in obesity: practical limits

Placental edge variants

Circumvallate

Chorionic plate smaller than basal plate; folded/heaped edge creates a raised ring.

Circummarginate

Similar concept but flatter transition; often less conspicuous on ultrasound.

Raised/folded edge may appear as a “shelf” Prenatal imaging diagnosis is imperfect; confirmatory pathology uncommon.

Diagnosis: avoid overcalling

Outcomes: evidence is mixed

Reported associations
  • Antepartum bleeding
  • Placental abruption
  • Preterm birth
  • SGA / FGR
Recent cohorts
  • Some series: no clear adverse correlation when diagnosed prenatally
  • Selection and misclassification likely
  • Counsel as “possible increased risk,” not deterministic

Surveillance: a pragmatic approach

Suggested timeline
22–24w 28w 32w 36w Targeted anatomy Growth ± AF Growth ± Doppler Growth / delivery planning

Antenatal testing (obesity)

Prepregnancy BMIWhen testing may be considered
35.0–39.9Often considered starting ~37 weeks (if no other indications).
≥40Often considered starting ~34 weeks (if no other indications).

Use shared decision-making; start earlier for superimposed comorbidity or abnormal growth/fluid.

When to escalate care

Bleeding

Any persistent or heavy bleeding warrants prompt evaluation; consider abruption differentials.

ROM

Leakage concern → triage for ROM assessment; confirm fluid method (MVP vs AFI).

Growth concern

If EFW <10% or falling percentiles → interval growth, UA Doppler, testing plan.

Delivery planning: prior CS + VBAC

Intrapartum preparedness (obesity)

  • Early anesthesia assessment; consider early neuraxial placement.
  • Two large-bore IVs when feasible; hemorrhage cart readiness.
  • Continuous fetal monitoring in labor.

Plan for safe access, positioning, and communication; mitigate avoidable delays during urgent scenarios.

Documentation pitfalls to avoid

Avoid copying ICD codes that conflict with gestational age or clinical history.

Take-home pearls