Safety of early amniocentesis versus CVS

Down syndrome serum marker screening: decision criteria and implicit values

Maternal serum markers assess the individual risk of giving birth to a fetus with Down syndrome. Because this information is a probability, and because of the infinite number of cut-off risks that can be adopted, a decision criterion is needed to define a population screening program. While a decision criterion for cut-off risks may refer to arbitrations between risks, another criterion must be considered. This criterion focuses on a societal perspective by comparing the costs of the program to the expected benefits. We will first discuss the questions that are raised when assessing, in terms of cost-effectiveness, the consequences of having adopted the policy maker's preferences for prenatal diagnosis referral. Subsequently, we will discuss the implicit values attributed to the outcomes of the program when the societal point of view is reduced to societal profitability. This is accomplished by means of a cost-benefit analysis using the 'avoided costs' approach. The consequences of screening with 'double' and 'triple' tests were assessed using a database made of 10,108 observations, including 63 Down syndrome cases. For a cut-off risk of 1:250 (resulting in a 7% amniocentesis referral rate, regardless of the technique), conclusions in terms of decision making differ according to the effectiveness indicator. Although a criterion based on resource allocation would promote the triple test, cost-benefit analysis points out the impact on results of factors such as the amniocentesis related fetal losses or the introduction of equity principles.

Prenatal diagnosis by chorionic villus sampling

Chorionic villus sampling (CVS) retains its great advantage over mid-trimester amniocentesis by producing early results. Moreover, rapid analytical techniques reduce significantly the waiting time between sampling and diagnosis, while recombinant DNA technology and human gene mapping progress amplify enormously the spectrum of the indications. The recent inclusion in the prenatal diagnosis package of screening tests based on DNA analysis for the major genetic diseases (i.e. cystic fibrosis, fragile-X mental retardation syndrome) may efficiently contribute to prevent the genetic disease. The role of CVS in twin pregnancy has been investigated and compared to amniocentesis. Although these techniques are equally safe, CVS should be considered the approach of choice for a number of technical advantage and in relation to selective fetal reduction in discordant twins. Recent reports have substantially contributed on the hypothetical relationship between limb reduction defects (LRDs) and chorion biopsy. The analysis of LRDs among more than 130,000 CVS reported to WHO CVS-Registry has been unable to find out any relationship between sampling and fetal malformations, including LRDs. In conclusion, first trimester CVS should be considered the gold standard procedure for prenatal diagnosis of genetic diseases.