Sometimes it's an earlier test called CVS, or chorionic villus sampling, which collects a bit of tissue from the placenta.

有时候这是一个CVS早期检查或者叫作绒毛活检，从胎盘处获取绒毛组织。

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A chorionic villus is a minute vascular projection on the fetal chorion.

绒膜绒毛是胎儿绒毛膜上的一种微小的血管凸出物。

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Antenatal diagnosis by Chorionic villus sampling can be done.

产前诊断由绒毛采样是可以做到的。

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Some research suggests that the miscarriage rate following chorionic villus sampling may be as high as 2%, the researchers said, which, if true, would raise that toll closer to 600.

BBC: Down's test miscarriage warning

To confirm or rule it out, a further test is offered - either amniocentesis and chorionic villus sampling, both of which use a fine needle to take tissue or fluid from inside the womb.

BBC: Down's test miscarriage warning

However, the researchers said that despite a lower number of invasive tests, the heavier reliance of this method on chorionic villus sampling earlier in pregnancy could actually mean an increase in the number of healthy babies lost if the miscarriage rate using this method was closer to 2%.

BBC: Down's test miscarriage warning