Outcome of antenatal invasive diagnostic tests in a fetal medicine unit with low case load in North Wales, United Kingdom.

The aim of this retrospective cohort study was to review rate of miscarriage following antenatal invasive diagnostic procedures from a unit where relatively low annual numbers of procedures are undertaken. Data were analysed for 201 chorionic villous samplings (CVSs) performed between January 2007 and June 2019 and 511 amniocenteses performed between January 2008 and June 2019, in singleton pregnancies. The miscarriage rates after CVS was 0% at 48 hours, 0.6% at 2 weeks and 2.5% up to 24 weeks of gestation. All four miscarriages following CVS had significant inherent high-risk features, therefore, it would be inappropriate to attribute these losses solely to the procedure itself. None of the women who had an amniocentesis had a miscarriage during the study period. We did not find a causal association between number of invasive procedures performed by an operator and miscarriage rate in our setting even with low annual numbers of invasive procedures.Impact Statement Royal College of Obstetricians and Gynaecologists (RCOG) of UK recommends a minimum of at least 30 CVSs or amniocenteses procedures per year for a practitioner in order to maintain skills. A centre performing more fetal invasive procedures has lower miscarriage rates due to more experience of practitioners. This study is the first long-term audit data from a smaller fetal medicine unit with relatively low annual case load, suggesting that miscarriage risk may actually be lower than the current understanding. No additional risk of miscarriage or pregnancy loss following fetal invasive procedures even with relatively low annual numbers than that recommended by the RCOG. The findings of this study are important in the era of non-invasive prenatal testing which will see the overall number of fetal invasive procedures decline with time. Competence in safely undertaking antenatal invasive procedure can possibly be maintained with lower annual procedure numbers. Units undertaking low number of antenatal invasive procedure must continuously audit their practice to ensure satisfactory standards and outcomes. More research is needed from smaller units to corroborate or refute the findings of this study.