A classification of pregnancy losses after invasive prenatal diagnostic procedures: an approach to allow comparison of units with a different case mix.

Abstract

Pregnancy loss rates after prenatal invasive procedures such as amniocentesis (Amnio), chorionic villous sampling (CVS) and fetal blood sampling (FBS) vary with an underlying indication for the procedure and due to different background risk of miscarriage. Loss rates need to be quantified and available for counselling. We developed a classification of pregnancy losses that will help in calculating procedure-related pregnancy loss rates and allow comparison between units with a different case mix. The procedure-related pregnancy loss rate was obtained by subtracting the losses in pregnancies with known lethal conditions and those occurring more than two weeks after the procedure from total pregnancy losses. Out of 436 CVSs, there were 18 losses. Of these, 14 had a known lethal condition and 3 occurred after 2 weeks of CVS. In only one case, there was no known lethal abnormality and the loss occurred within 2 weeks. Thus, the total pregnancy loss rate was 4.1% and the procedure-related loss rate was 0.23% (95% CI; 0.0061-1.28). The procedure-related loss rates for Amnio 0.7% (95% CI; 0.2-1.8) and FBS 1.19 (95% CI; 0.14-4.23) were calculated in a similar way. We present a method of recording pregnancy loss after prenatal invasive procedures, which would be useful for benchmarking comparison between units and pre-procedural counselling.