GTG 8 Amniocentesis and Chorionic Villous Sampling

This blog post is a Summary of Green Top Guideline 8: Amniocentesis and Chorionic Villous Sampling which was updated in October 2021. As it is a GTG so, it is must to go through the full guideline by yourself in order to have the complete understanding. 

To download the guideline: Click Here

For Infographic: Click Here

For All GTGs: Click Here

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Background

• Prenatal diagnosis in the form on amniocentesis or CVS is offered due to various reasons such as higher risk for aneuploidy screening, suspected structural anomaly or in cases of known risk of inherited genetic disease
• The only definitive diagnostic tests → both CVS & amniocentesis
• CVS done between 11+0 - 13+6 wks Can also be done 14+0 - 14+6 wks 
• Amniocentesis offered from 15+0 wks 
• Individualised counselling
• Informed written consent Form 3
• Must provide information for aftercare

Organising amniocentesis & CVS

• Women are usually anxious so should support them ± partners
• Follow Fetal Anomaly Screening Program guidance
• Appropriate environment, skilled staff, access to allied specialities and appropriate support for continuation or termination of pregnancy
• Sensitive & unbiased approach
• Discuss religious aspects
• Give time to discuss the decision with partners & friends

Additional Risks with Invasive Testing

Risk of Miscarriage

• Additional risk of pregnancy loss after CVS or Amniocentesis is performed by an appropriately trained operator is < 0.5%

Different studies have been quoted

• Earlier studies showed increased pregnancy loss after CVS, but later studies show that there is no significant increase in pregnancy loss above the background risk with both procedures
• Lower pregnancy loss likely due to improvements in technology, techniques & experience

Systemic Review 2000-2014

• Procedure-related risk of pregnancy loss Amniocentesis 0.11% CVS 0.22% Both 0.35%

Cochrane Review comparing route for CVS (Transabdominal or Transcervical)

• Pregnancy loss below background rate regardless of route
• Procedure-related pregnancy loss Transcervical 1.4% Transabdominal 1%

Other risks

• CVS results may be affected by placental mosaicism in 1-2% 
• Structural anomaly present → Discuss ongoing care (continuation or termination of pregnancy)
• Structural anomaly absent & QFPCR after CVS suggest chromosomal anomaly → full karyotype awaited before any decision 
• Severe maternal sepsis → very rare
• Skin decontamination, use of separate sterile gel sachet, enclosing USG probe in sterile back & continuous USG recommended
• Amniotic fluid cloudy or purulent → Consider microbial analysis of amniotic fluid & Consider antibiotics

Ref: GTG 8

Operator Skills

• Risks may increase if performed by less skilled operators 
• Appropriately trained operator to complete at least 20 procedures (CVS or amniocentesis) annually

Ref: GTG 8

Gestation for Procedures 

Amniocentesis 

• Not before 15+0 wks as associated with higher pregnancy loss & risk of talipes equinovarua
• Early amniocentesis is associated with
• Multiple needle insertion 3% Risk of failed culture 1.8%
• False negative results 
• Risk of obtaining low quantities of DNA before 16 wks 

CVS

• Not before 10+0 wks as associated with oromandibular and limb defects
• Prior to 11+0 wks could be technically challenging

Amniocentesis & CVS in Multiple Pregnancies

• High level of expertise in USG scanning 
• Recommended to be performed by an operator skilled in selective TOP 
• Map the pregnancy with care
• Mapping is essential prior to any invasive testing 
• Labelling by assigning number to be avoided
• Better to use lateral orientation as maternal left / right twins or vertical orientation as upper/lower twins 
• If no clearly identifiable USG differences between twins → must take extra care & two operators should confirm labelling

Amniocentesis in twins 

• Pregnancy loss 3%
• Procedure-related pregnancy loss <24 wks 1% OR total pregnancy loss 1.8
• True amniocentesis-related risk of pregnancy loss in twins ~ <1%

CVS in twins 

• Overall pregnancy loss 3.8%
• Risk of cross-contamination during CVS ~1% — use double uterine entry to mitigate it

Technique

• Operators should use techniques with which they are most comfortable

Higher order multiple pregnancy

• Insufficient data for higher order multiple pregnancies 

Role of 3rd Trimester Amniocentesis

• 3rd trimester amniocentesis may be offered — newly identified structural anomaly, suspected fetal infection or FGR

Complications

• Unusual to have serious complications afterwards
• PTL <37 wks 4-8% <34 wks 3-4% 
• More than one needle required 5%
• Bloodstained samples 5-10%
• Risk of culture failure Overall 9-10% (increases with increasing gestation)

Risk of Mother to Child Transmission MTCT

HIV

• HIV + HAART + undetectable viral load → very low risk of MTCT
• Not on HAART → 2.3% MTCT
• Risk with therapy - Zidovudine mono therapy 6% double-nucleoside reverse transcriptase inhibitor 3%
• Screening results for blood borne viruses not known → Delay invasive testing
• Screening declined → Informed consent should include discussion of MTCT risk

Hepatitis B

• Overall risk low
• Increase viral load is a risk factor
• Viral load < 6.99 log 10 copies/ml — Low risk
• If HBV DNA >500 copies/ml — significant increase in MTCT OR 4.7

Hepatitis C

• No evidence of risk of MTCT after amniocentesis 

Points taken from the RCOG videos GTG 8 | To access Click Here

Consent 

• Written informed consent 

Amniocentesis

• Position Supine (use wedge if necessary)
• Local anaesthesia not used in routine
• Assess most suitable approach 
• Avoid placental cord insertion if using transplacental approach 
• 20-22G Needle used
• Whole of the procedure to be done under continuous USG guidance
• Volume of specimen 15-20ml 

CVS

• Position Supine & perform USG to determine the most suitable site
• Best if bladder empty
• Both transabdominal TA (more common in UK) or transcedrvical TC approaches can be used 
• With TA approach a double or single needle technique may be used
• Whole of the procedure to be done under continuous USG guidance
• Approximately 1 cm2 square of chorionic villi sufficient

Technical Considerations

• If difficulties anticipated → consider requesting support form more experienced operator
• A second attempt fails to obtain satisfactory sample → consult more experienced operators 

Aftercare

• Demonstrate fetal heart to woman
• Clean & cover needle insertion site with adhesive wound dressing
• Provide Anti-D prophylaxis for RhD negative unless fetus known to be Rh negative 
• Document the procedure using standard format which should include indication, needle size, approach used, number of entries, complications, provision of Anti-D

Advice & Follow-up

• Counsel the woman that mild discomfort in first 24-48hrs is common 
• Can use paracetamol for pain relief
• Severe pain or vaginal loss or feeling unwell — must seek immediate medical review
• Provide necessary contact details 
• Inform the turnaround time for results
• Agree for communication method

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