lev-os Documenting Obstetric Ultrasound
Structures obstetric ultrasound reporting with standardized biometry, detailed anatomy survey per AIUM/ACR/ACOG guidelines, growth percentile assessment, and Doppler documentation.
Why This Skill Exists
Obstetric ultrasound is the primary tool for fetal assessment, and its documentation must meet the joint AIUM/ACR/ACOG Practice Parameter standards. A first-trimester ultrasound establishes dating accuracy, the standard second-trimester anatomy scan (18–22 weeks) is the most comprehensive evaluation of fetal anatomy for structural anomalies, and third-trimester growth scans detect fetal growth restriction or macrosomia. Each exam type has required elements that must be documented for the report to be considered complete.
Inadequate documentation of fetal anatomy — particularly failure to document non-visualization of a structure — is a frequent source of malpractice claims. If a structure cannot be visualized, the report must explicitly state this and recommend follow-up. This skill ensures every required element is addressed in every obstetric ultrasound report.
Checkpoint A: Pre-Draft Intake (Mandatory)
- Indication for exam — dating, anatomy survey, growth, biophysical profile, bleeding, decreased fetal movement? (Default: from order)
- Gestational age — by LMP, prior ultrasound, or IVF dating? (Default: from prenatal record)
- Exam type — first-trimester, standard second-trimester, limited, growth/follow-up, BPP? (Default: from indication)
- Number of fetuses — singleton or multiple? Chorionicity and amnionicity documented? (Default: from prior US or current exam)
- Prior ultrasound findings — any previously identified anomalies, shortened cervix, or growth concerns? (Default: from prior reports)
- Maternal BMI — affects image quality and documentation of limitations. (Default: from chart)
- Relevant history — prior anomalies, family history of congenital defects, diabetes, medications (e.g., antiepileptics)? (Default: from prenatal record)
- Approach — transabdominal, transvaginal, or both? (Default: document technique used)
Documents to Request
- Prior obstetric ultrasound reports
- Prenatal record with dating information
- Genetic screening results (NIPT, first-trimester screen, quad screen)
- Any referral notes from MFM
- Growth charts from prior exams
- Fetal echocardiography reports (if performed)
Step 1: First-Trimester Ultrasound (< 14 Weeks)
Required documentation elements per AIUM:
- Gestational sac — location (intrauterine confirmed), mean sac diameter (MSD) if no embryo
- Yolk sac — present/absent
- Embryo/fetus — crown-rump length (CRL) in mm, with corresponding gestational age
- Cardiac activity — present/absent; if present, document FHR in bpm
- Number of embryos — if multiple, document chorionicity (dividing membrane thickness, lambda/twin peak sign vs. T-sign) and amnionicity
- Nuchal translucency (NT) — if 11 + 0 to 13 + 6 weeks: measurement in mm, must meet NT certification standards (Fetal Medicine Foundation)
- Uterus — fibroids, anomalies
- Adnexa — ovaries, corpus luteum, masses
- Cul-de-sac — free fluid present/absent
Dating by CRL (< 9 weeks): ± 5 days accuracy.
Step 2: Standard Second-Trimester Anatomy Survey (18–22 Weeks)
This is the most detailed required exam. Per AIUM/ACR/ACOG Practice Parameter, ALL of the following must be documented:
Fetal Biometry
| Measurement | Abbreviation | Percentile Reporting |
|---|---|---|
| Biparietal diameter | BPD | With GA correlation |
| Head circumference | HC | With GA correlation |
| Abdominal circumference | AC | With GA correlation |
| Femur length | FL | With GA correlation |
| Estimated fetal weight | EFW | Hadlock formula; report percentile |
Fetal Anatomy Checklist
| System | Required Structures |
|---|---|
| Head/Brain | Cerebral ventricles (atria < 10 mm), cavum septum pellucidum, cerebellum (with transverse cerebellar diameter), cisterna magna (2–10 mm), falx cerebri, choroid plexus |
| Face | Upper lip (for cleft screening), nose, orbits |
| Spine | Cervical, thoracic, lumbar, sacral — longitudinal and axial views; skin covering intact |
| Heart | Four-chamber view, left ventricular outflow tract (LVOT/aorta), right ventricular outflow tract (RVOT/PA), cardiac axis (normal 45° ± 20° leftward), heart rate and rhythm |
| Chest | Lungs bilateral, no effusion, diaphragm integrity |
| Abdomen | Stomach (left-sided, fluid-filled), kidneys (bilateral), bladder, umbilical cord insertion site, 3-vessel cord (2 arteries, 1 vein) |
| Extremities | Arms (humerus, radius, ulna), legs (femur, tibia, fibula), hands and feet |
| Genitalia | Document if visualized (optional but often reported) |
Placenta
- Location (anterior, posterior, fundal, lateral)
- Relationship to internal cervical os (previa, low-lying, or clear)
- Cord insertion (normal, marginal, velamentous)
- Number of cord vessels (2-vessel cord requires fetal echocardiography and renal evaluation)
Amniotic Fluid
- Assessment: amniotic fluid index (AFI) or single deepest pocket (SDP)
- Normal AFI: 5–25 cm; SDP: 2–8 cm
- Oligohydramnios: AFI < 5 cm or SDP < 2 cm
- Polyhydramnios: AFI > 25 cm or SDP > 8 cm
Cervical Length (if indicated)
- Transvaginal measurement if history of preterm birth, short cervix, or symptoms
- Normal: > 25 mm; < 25 mm before 24 weeks requires intervention consideration
Step 3: Growth Assessment (Third Trimester)
Growth ultrasounds are typically performed at 28–32 weeks and/or 36 weeks for high-risk patients.
Required Elements
- All four biometric measurements (BPD, HC, AC, FL)
- EFW with Hadlock formula and percentile (using population-based or customized growth charts)
- Growth velocity compared to prior exam (interval growth)
- Amniotic fluid assessment
Growth Classification
| Category | Percentile | Action |
|---|---|---|
| Small for gestational age (SGA) | EFW < 10th percentile | Evaluate for FGR: Doppler studies, amniotic fluid, consider structural evaluation |
| Fetal growth restriction (FGR) | EFW < 10th percentile + abnormal Doppler or < 3rd percentile | Increased surveillance per SMFM protocol |
| Appropriate for GA (AGA) | 10th–90th percentile | Routine care |
| Large for GA (LGA) | EFW > 90th percentile | Evaluate for GDM, macrosomia risk, delivery planning |
Doppler Assessment (when indicated)
| Vessel | Indication | Abnormal Findings |
|---|---|---|
| Umbilical artery | FGR, preeclampsia | Elevated S/D ratio, absent or reversed end-diastolic flow |
| Middle cerebral artery | Fetal anemia (Rh isoimmunization), FGR | MCA-PSV > 1.5 MoM indicates fetal anemia |
| Ductus venosus | Severe FGR with abnormal UA Doppler | Absent or reversed a-wave indicates cardiac compromise |
| Uterine artery | Preeclampsia risk assessment | Bilateral notching, elevated RI/PI |
Step 4: Biophysical Profile (BPP)
When a BPP is performed, document all five components:
| Component | Normal (2 points) | Abnormal (0 points) |
|---|---|---|
| Fetal breathing movements | ≥ 1 episode of ≥ 30 sec in 30 min | Absent or < 30 sec |
| Gross body movements | ≥ 3 discrete body/limb movements in 30 min | < 3 movements |
| Fetal tone | ≥ 1 episode of flexion/extension with return to flexion | Absent or slow return |
| Amniotic fluid | SDP ≥ 2 cm | SDP < 2 cm |
| NST (reactive) | ≥ 2 accelerations of ≥ 15 bpm × 15 sec in 20 min | Non-reactive |
- 8–10/10: Normal (or 8/8 without NST)
- 6/10: Equivocal — repeat in 24 hours or deliver if ≥ 37 weeks
- 4/10: Abnormal — deliver if viable
- 0–2/10: Abnormal — urgent delivery
Checkpoint B: Post-Draft Alignment (Mandatory)
- Are all AIUM-required elements documented for the exam type (first trimester, anatomy, growth, BPP)?
- Are non-visualized structures explicitly stated — "cardiac outflow tracts not visualized due to fetal position; recommend follow-up"?
- Is the EFW percentile calculated and reported on an appropriate growth curve?
- Is placental location documented with relationship to the cervical os?
- Are Doppler findings reported with specific values and interpretation when performed?
Quality Audit
- Indication for exam documented
- Gestational age basis and EDD documented
- Number of fetuses documented with chorionicity/amnionicity (if multiple)
- All four biometric parameters measured and reported with GA correlation (BPD, HC, AC, FL)
- EFW calculated and percentile reported
- Complete anatomy checklist addressed (all AIUM-required structures)
- Non-visualized structures explicitly documented with follow-up recommendation
- Fetal cardiac activity documented (rate and rhythm)
- Cardiac outflow tracts documented (LVOT/RVOT) in anatomy scan
- Placental location and cord insertion documented
- Number of cord vessels documented
- Amniotic fluid volume documented (AFI or SDP)
- Cervical length documented (if indicated)
- Doppler values documented with interpretation (if performed)
- Comparison to prior exam documented (if growth assessment)
Guidelines
- Document what you cannot see — an unreported non-visualized structure is presumed to have been seen and normal; if it was not visualized, state it explicitly and recommend follow-up.
- Use standardized growth formulas — Hadlock (AC, FL, BPD, HC) is the most widely validated for EFW; document which formula was used.
- Measure CRL for dating below 14 weeks — do not use BPD for first-trimester dating.
- Report chorionicity early — in twin pregnancies, the lambda sign (dichorionic) vs. T-sign (monochorionic) is most reliably assessed in the first trimester.
- Include clinical correlation — an ultrasound report should not just list measurements; it should correlate findings with clinical context (e.g., "EFW < 5th percentile in the setting of preeclampsia; recommend Doppler surveillance").
- Flag urgent findings immediately — absent cardiac activity, hydrops, absent end-diastolic flow, and suspected major anomalies require verbal communication to the ordering provider (document time of communication).
- Cervical length is measured transvaginally — transabdominal cervical length overestimates true length and should not be used for clinical decision-making regarding short cervix.
- Report the MCA-PSV in MoM — raw velocity values are meaningless without conversion to multiples of the median for gestational age.