Radiology
Chorionic Villus Sampling
Built from Obstetric Imaging
What’s inside
11 sections · 71 slides
Overview
- Contents
Purpose and Timing
What the test takes, when it is taken, and what it answers
- Definition of chorionic villus sampling
- Tissue that is sampled
- Gestational age window for the procedure
- Indications for chorionic villus sampling
- Chorionic villus sampling versus amniocentesis
- Advantage of an earlier result
- Sequence of a sampling visit
Preparation and Route Selection
Consent, the pre-procedure scan, and choosing how to reach the placenta
- Counselling and informed consent
- Ultrasound assessment before the procedure
- The two sampling routes
- Transabdominal route to the placenta
- Transcervical route to the placenta
- Safety comparison of the two routes
- Placental position and route choice
- Conditions that rule out the transcervical route
- 11+0–13+6
- Ultrasound recognition of the instrument
- Instrument tip seen inside the placenta
- Transcervical catheter in a posterior placenta
- Transabdominal needle in a posterior placenta
Transcervical Technique
Catheter through the cervix, parallel to the membranes, to the far edge of the placenta
- Ultrasound check before transcervical sampling
- Instruments for transcervical sampling
- Transcervical sampling tray
- Uterine position and the sampling path
- Patient position and antiseptic preparation
- Sampling catheter specifications
- Passing the catheter to the placenta
- Aspiration of villi with negative pressure
- Inspection of the aspirated sample
- Repeat insertion for an inadequate sample
- Transcervical sampling step by step
Transabdominal Technique
Spinal needle along the long axis of the placenta, several passes, suction held throughout
- Instruments for transabdominal sampling
- Transabdominal sampling tray
- Patient position and sterile field
- Needle insertion under ultrasound guidance
- Aspiration and needle withdrawal
- Reason for multiple passes through the placenta
- Gestational age limits of each route
- Transabdominal sampling step by step
Complications
Bleeding, infection, fluid leak, alpha fetoprotein rise and Rhesus sensitisation
- Bleeding after chorionic villus sampling
- Subchorionic haematoma
- Chorioamnionitis and other infection
- Amniotic fluid leakage and oligohydramnios
- Maternal serum alpha fetoprotein elevation
- Rhesus isoimmunisation and anti-D prophylaxis
Fetal Risk and Early Sampling
Why the procedure is never performed before 10 weeks
- Limb defects after very early sampling
- Minimum gestational age for the procedure
- Neonatal haemangioma reports
Pregnancy Loss
Separating background miscarriage, operator experience and true procedure-related risk
- Background miscarriage rate as the comparison
- Historical loss rates and operator inexperience
- Repeat insertions and pregnancy loss
- 2.36%
- Meta-analysis of loss rates in 2015
- Systematic review of loss rates in 2019
- Loss rates in twin pregnancies
- Applicability of the published loss figures
Multiple Pregnancy
Sampling each placenta, proving you did, and keeping the samples apart
- Sampling each placenta in a multiple pregnancy
- Confirming that two placentas were sampled
- Planning the approach to avoid resampling
- Twin-to-twin contamination of the sample
Mosaic Results
Two cell lines in one sample, and how amniocentesis settles the question
- Chromosomal mosaicism in villus samples
- Confined placental versus true fetal mosaicism
- Working up a mosaic villus result
Summary and References
The points to carry away, and the sources behind them
- Summary of purpose and timing
- Summary of technique and safeguards
- References
- References (continued)
- Suggested readings
- Suggested readings (continued)
- Obstetric Imaging: Fetal Diagnosis and Care, 2nd Edition