Maternal age‐specific fetal loss rates in Down syndrome pregnancies

OBJECTIVES: Pregnancies affected by Down syndrome (DS) have a greater risk of spontaneous fetal loss than those that are unaffected. In this article, we investigate the relationship between maternal age and the risk of spontaneous fetal loss in DS pregnancies. METHODS: Fetal loss at different maternal ages were estimated by survival analysis using follow-up of 5177 prenatally diagnosed cases. The maternal age effect on loss rate was subsequently confirmed by a re-analysis of published comparisons of the maternal age-specific prevalence of DS at different gestational ages. RESULTS: The average fetal loss rate between the time of chorionic villus sampling (CVS) and term was 32% (95% CI: 26-38), increasing from 23% (95% CI: 16-31) for women aged 25 to 44% (33-56) for women aged 45. The average fetal loss rate between the time of amniocentesis and term was 25% (21-31), increasing from 19% (14-27) to 33% (26-45) across the same age range. CONCLUSION: The fetal loss rate in DS pregnancies increases with maternal age, and this has consequences when estimating the live birth prevalence of DS in the presence of prenatal diagnosis and termination, and when assessing the performance of prenatal screening techniques.