It is estimated that around 5% of the pregnant population (approximately 30,000 women per annum in the UK) are offered a choice of invasive prenatal diagnostic tests, most commonly amniocentesis or chorionic villus sampling (CVS). The type of diagnostic test available and offered is likely to vary depending upon the timing of any initial screening test that is performed.
Amniocentesis is the most common invasive prenatal diagnostic procedure undertaken in the UK. Most amniocenteses are performed to obtain amniotic fluid for karyotyping from 15 weeks (15+0 ) onwards. Amniocentesis performed before 15 completed weeks of gestation is referred to as ‘early amniocentesis’.
CVS is usually performed between 11 (11+0 ) and 13 (13+6 ) weeks of gestation and involves aspiration or biopsy of placental villi. CVS can be performed using either a transabdominal or a transcervical approach.
This guideline sets out a series of evidence-based standards for provision of amniocentesis and CVS.