Impact of screening programs on the prenatal diagnosis (detection rate) of trisomy 13 and 18 over a 30-year period

ObjectiveTo evaluate the impact of screening policies in Tuscany on the detection of trisomy 13 and trisomy 18 (T13/T18) with respect to time of diagnosis. A secondary aim was to evaluate the prevalence of these aneuploidies and to report the associated malformations.MethodsData were extracted from the population-based Registry of Congenital Anomalies of Tuscany. All confirmed cases of T13/T18 among live births, stillbirths, miscarriages and terminations of pregnancy were included over a 30-year period (1994-2023). The prevalence for both aneuploidies was calculated overall and by age group (<35 years old; ≥ 35 years old). For prenatally diagnosed cases, median gestational age at diagnosis was calculated. The frequencies of the most common associated abnormalities were also calculated.ResultsAbout 529 fetuses were diagnosed with T13/T18, respectively 133 (25.1%) and 396 (74.9%). The prevalence among 10,000 births was 1.67 (95% CI 1.40-1.98) for T13 and 4.98 (95% CI 4.45-5.49) for T18. Prenatal detection rate for T13 increased from 88.2% (95% CI 72.5-96.7) to 100% (95% CI 88.1-100.0). For T18, it increased from 87.5% (95% CI 79.2-93.4) to 100% (95% CI 95.0-100.0). Median gestational age at discovery gradually decreased for both trisomies through the study period, from 17 to 12 weeks. The most common anomalies in T13 were nervous system anomalies (27.8%) and congenital heart defects (9.8%). T18-associated anomalies included congenital heart defects (11.9%) and nervous system anomalies (10.1%).ConclusionThe implementation of screening policies led to an improvement in the rate of detection of T13/18 and a decrease in the median gestational age at diagnosis.