Are there any good statistics for the failure rates of the invasive prenatal screening tests (e.g., CVS, amniocentesis)?

The books and pamphlets have numbers and the doctors and nurses parrot those numbers but no one seems to know what they mean or where they came from. The risk of killing the baby seems unbelievably high, but it's difficult to understand what those numbers mean without understanding how they were derived.

When they say that amniocentesis done before 24 weeks has a 0.5% chance of miscarriage are they saying:

  • 0.5% of amniocentesis tests cause miscarriage? or
  • 0.5% of mothers that get an amniocentesis test have a miscarriage vs ??% of mothers that don't get the test? or

Do these numbers account for the high miscarriage rate before 12 weeks (i.e., is that baked into the number)?

asked 16 Oct '10, 01:36

Guido's gravatar image

accept rate: 0%

Wikipedia lists the risk of miscarriage following amniocentesis to be aproximately 1 in 1,600 (0.06%) that means that one out of every 1,600 women who undergo the procedure will end up having a miscarriage. I imagine as in most studies there is no way to determine whether or not the amniocentesis caused the miscarriage or the women would of had a miscarriage anyway. Although some statistics may be able account for this. The reference to the study is listed so you can read their methodology.

Studies from the 1970s originally estimated the risk of amniocentesis-related miscarriage at around 1 in 200 (0.5%). A more recent study (2006) has indicated this may actually be much lower, perhaps as low as 1 in 1,600. In contrast, the risk of miscarriage from chorionic villus sampling (CVS) is believed to be approximately 1 in 100, although CVS may be done up to four weeks earlier, and may be preferable if the possibility of genetic defects is thought to be higher.

The article also states that the reason for waiting until at least the 15th week to perform the test is to prevent injury to the baby's limbs.


answered 16 Oct '10, 03:15

Tammy's gravatar image

Tammy ♦♦
accept rate: 18%

edited 16 Oct '10, 12:43

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Asked: 16 Oct '10, 01:36

Seen: 3,725 times

Last updated: 16 Oct '10, 12:43