Interventional and Procedural Ultrasound
Key Takeaways
- Ultrasound-guided amniocentesis uses sterile technique with continuous visualization of needle path avoiding placenta and fetus.
- Chorionic villus sampling (CVS) performed 10–13 weeks transabdominal or transcervical with rhogam and genetic counseling.
- Fetal blood sampling (cordocentesis/PUBS) targets umbilical vein at placental insertion or free loop under sterile conditions.
- Paracentesis and thoracentesis in maternal or fetal context require real-time needle guidance and documentation of fluid location.
- Biopsy of adnexal masses or lymph nodes uses color Doppler to avoid vascular structures before sampling.
Quick Answer: Procedural US requires real-time needle visualization, sterile technique, and vascular avoidance with color Doppler. Amnio ~15+ weeks; CVS ~10–13 weeks; PUBS umbilical vein. Document fetal heart after invasive procedures per protocol.
General Procedural Principles
| Principle | Application |
|---|---|
| Real-time guidance | Needle tip visible continuously in plane |
| Sterile field | Probe cover, sterile gel, skin prep |
| Vascular mapping | Color Doppler before puncture |
| Informed consent | Genetic counseling for invasive fetal procedures |
| Post-procedure monitoring | FHR, bleeding, cramping instructions documented |
Registry procedural images test safety sequencing—if needle path crosses placenta, fetus, or cord, reposition entry site before puncture.
Amniocentesis
Typically performed ≥15 weeks (standard genetic amniocentesis 15–20 weeks when adequate fluid pocket present).
Technique steps:
- Locate placenta, fetus, and adequate fluid pocket away from both
- Choose entry site avoiding fetal parts and cord
- 20–22G spinal needle; single-wall technique when feasible
- Aspirate amber amniotic fluid—blood streaking may occur
- Document fetal heart rate after procedure
Complications (exam facts): leakage, ROM, fetal loss risk approximately 0.1–0.3% in contemporary series—cite informed consent context.
Worked Scenario: Anterior Placenta in Path
Needle trajectory would traverse anterior placenta. Correct action: redirect to avascular pocket lateral to placental edge—avoid transplacental passage when possible.
Chorionic Villus Sampling (CVS)
Performed 10–13 weeks for earlier karyotype than amniocentesis.
| Route | Notes |
|---|---|
| Transcervical | Bladder empty; avoid awkward membrane crossing |
| Transabdominal | Similar needle discipline under continuous US |
Rh immune globulin for Rh-negative unsensitized patients within 72 hours after procedure due to fetomaternal hemorrhage risk.
Historical limb-reduction concern with very early technique—registry may reference appropriate gestational timing.
Cordocentesis (PUBS)
Percutaneous umbilical blood sampling targets umbilical vein at free loop or placental insertion under sterile conditions. Used for rapid karyotype, fetal anemia treatment (transfusion), infection assessment. Higher complication rate than amniocentesis—performed in specialized centers.
Non-OB GYN Procedures
| Procedure | Ultrasound Role |
|---|---|
| Oocyte retrieval | TV needle aspiration of follicles—avoid bowel and vessels |
| Pelvic abscess drainage | TV or transgluteal route under real-time guidance |
| Adnexal mass biopsy | Color Doppler to avoid vascular pedicle; local lidocaine wheal |
| SHG | Saline cavity distension (see infertility section) |
Fetal Shunt Procedures (Recognition)
Vesicoamniotic shunt for lower urinary tract obstruction (LUTO)—catheter from fetal bladder to amniotic cavity. Sonographer recognizes device on image; performance is MFM subspecialty.
Twin Pregnancy Invasive Procedures
In dichorionic twins, target correct sac—avoid cross-contamination. Both sacs may need sampling when indicated. Label images by fetus A/B.
Post-Procedure Counseling Elements
Patients receive instructions on fluid leakage, fever, contractions, decreased fetal movement—return precautions documented. FHR documented immediately after amnio/CVS per department protocol.
Informed Consent (Recognition)
Discuss miscarriage, infection, ROM risks vs benefits of genetic diagnosis—documentation that counseling occurred per policy.
Exam Traps
- Amniocentesis at 12 weeks (too early for standard genetic amnio)
- Procedural image showing needle without tip visualization labeled safe
- Forgetting Rhogam after CVS/amnio in Rh-negative patient
- Biopsy without prior color Doppler vascular mapping
- Confusing SHG (diagnostic) with amniocentesis (invasive fetal)
Procedure questions reward patient safety hierarchy: reposition, visualize tip, sterile technique, then aspirate.
Informed Consent and Counseling Elements
Invasive fetal procedures require genetic counseling, discussion of miscarriage risk, infection, ROM, and failure to culture. Sonographer role includes real-time imaging and documentation—counseling is physician/genetic counselor responsibility but registry tests recognition of required elements.
Amniocentesis: Late Indications
Beyond 15–20 week genetic amnio, third-trimester amniocentesis may assess fetal lung maturity (lecithin/sphingomyelin) or infection in specialized contexts. Twin amniocentesis requires two separate needle passes into each sac in dichorionic pregnancy—label samples A/B.
CVS Technique Pearls
Transcervical CVS requires empty bladder, avoid crossing membranes awkwardly. Transabdominal CVS uses similar needle gauge under continuous guidance. Contamination with maternal decidua may cause confined placental mosaicism—genetics interprets results. Fetal loss rate slightly higher than amnio historically—counsel per current literature.
Fetal Reduction and Selective Termination (Recognition)
In monochorionic twins with selective anomaly, radiofrequency ablation or cord occlusion may be performed at specialized centers—not general sonographer procedure—but registry may test chorionicity implications for invasive testing targeting correct fetus.
Gynecologic Interventions
Endometrial biopsy may be ultrasound-guided when cavity distorted. Oocyte retrieval uses TV needle under real-time guidance—avoid bowel and iliac vessels with color Doppler. Endometrial ablation follow-up ultrasound assesses cavity integrity and hematometra.
Paracentesis and Thoracentesis (Maternal)
Maternal pleural effusion or ascites in preeclampsia or malignancy may require drainage under ultrasound guidance. Document fluid pocket depth, needle path, and post-procedure symptoms. Fetal status documented when applicable.
Local Anesthesia and Asepsis
1% lidocaine wheal for superficial procedures. Chlorhexidine skin prep, sterile probe cover, sterile gel for transvaginal interventions. Time-out and site marking per facility policy—patient safety questions on registry.
Post-Procedure Fetal Heart Rate
FHR documented immediately after amniocentesis and CVS per protocol. Persistent bradycardia or prolonged tachycardia prompts physician notification. Vaginal bleeding and leaking fluid are patient return precautions.
Post-Procedure FHR
Document fetal heart rate immediately after amniocentesis or CVS. Rh-negative patients need Rh immune globulin within 72 hours after invasive fetal procedures due to fetomaternal hemorrhage risk.
Needle Safety Sequence
Reposition if needle crosses placenta, fetus, or cord. Continuous tip visualization and sterile technique before aspiration—registry procedural images test this hierarchy.
Ultrasound-guided amniocentesis is typically performed at gestational ages of approximately:
During invasive fetal procedures, continuous ultrasound guidance is primarily required to:
Chorionic villus sampling is generally performed at approximately:
Before biopsy of a solid adnexal mass, color Doppler is used to: