The study was unable to assess whether amniocentesis was a lower risk procedure than CVS, because the background risk of miscarriage falls with advancing pregnancy. As CVS is done earlier in the pregnancy the total rate of miscarriage is higher after CVS than after amniocentesis, but previous studies have shown that the miscarriage rates due to the two procedures are similar.
"We attempted to assess the miscarriage rate in the 633,308 women not undergoing an invasive procedure, in order to provide a background rate with which to compare the miscarriage rates following invasive tests" says Professor Tabor. "It was, however, not possible to define a common starting point from which all pregnancies, without selection, could be compared with an ultrasonically verified live pregnancy.
"So our research provides the miscarriage rates after an invasive procedure, but we cannot say what the estimated rate of miscarriage would have been in patients not having invasive procedures.
"Having said that, the very clear variations in miscarriage rates between units with different levels of expertise demonstrate that the invasive procedures play a role in miscarriage rates."
The authors are keen to stress that pregnant women should be aware of the risks of these invasive procedures, but add that it is also very important that they consider appropriate screening and risk assessment, especially if their medical history or other factors indicate an elevated risk of abnormalities.
"We would urge anyone undergoing either of these tests to discuss them fully with the healthcare staff
|Contact: Annette Whibley|