Amniocentesis and Chorion Villus Sampling
Up to five per cent of pregnant women are offered a choice of invasive prenatal diagnostic tests amniocentesis or chorionic villus sampling.
Amniocentesis is the most common invasive prenatal diagnostic procedure.
Most amniocenteses are performed to obtain amniotic fluid for karyotyping.
The majority are undertaken from15 completed weeks (15+0) onwards.
Amniocentesis performed before 15 completed weeks of gestation is referred to as ‘early.’
Chorionic villus sampling (CVS)
is usually performed between 10 and 13 weeks of gestation and involves aspiration of placental tissue rather than amniotic fluid.
CVS can be performed using either
- Percutaneous transabdominal
- Transcervical approach.
Transabdominal CVS can be performed at gestations greater than 13 weeks.
Second trimester amniocentesis is safer than transcervical CVS and early amniocentesis.
If earlier diagnosis is required, transabdominal CVS is preferable to early amniocentesis or transcervical CVS.
In circumstances where transabdominal CVS may be technically difficult the preferred options are transcervical CVS in the first trimester or second trimester amniocentesis.
Rates of miscarriage
The rate of miscarriage associated with amniocentesis is approximately 0.5 - 1%
The rate of miscarriage following transabdominal CVS is higher than after second trimester amniocentesis at 1-1.5%.
Transcervical CVS carries miscarriage rate of 4 %.
Timing of amniocentesis and CVS
Early amniocentesis performed before 14 completed weeks of gestation (14+0) is not a safe alternative to second-trimester amniocentesis or CVS. Fetal loss is higher than Late amniocentesis and also higher than transabdominal CVS. In addition fetal talipes rate is higher following early aminiocentesis.
It is recommended that CVS should not be performed before 10 completed weeks of gestation (10+0) as there is association between CVS, facial limb hypoplasia and isolated limb disruption defects.
It is thought the defect is due to transient fetal hypoperfusion and vasospastic phenomena secondary to vascular disruption to the placental circulation
AMNIOCENTESIS Dr Serag Youssif R
CHORION VILLUS SAMPLING Dr Serag Youssif R
Dr Youssif Obstetric Birthsafe 16