The possibility of improving the effectiveness of antenatal screening for Down's syndrome by measuring human chorionic gonadotrophin concen- IntroductionDown's syndrome is the most common congenital cause of severe mental retardation, with an incidence at birth of about 1-3 per 1000. The current method of antenatal screening is to select women for a diagnostic amniocentesis on the basis of advanced age. Age is, however, a poor basis for screening and has had little impact on the incidence at birth. With age as a basis for screening only about 30% of all Down's syndrome pregnancies can be detected by carrying out amniocentesis on the 5% of women most at risk-that is, those aged 36 years or greater-though in practice fewer than 15% of affected pregnancies are detected because fewer than half of these older women actually have amniocentesis.' Additional antenatal screening tests such as maternal serum measurements of c fetoprotein and unconjugated oestriol can increase the rate of detection to about 45% if the 5% of pregnant

Conclusion -Antenatal maternal serum screening for Down's syndrome is effective in practice and can be readily integrated into routine antenatal care. It is cost effective and performs better than selection for amniocentesis on the basis of maternal age alone.

BACKGROUND: As part of EUROCAT's surveillance of congenital anomalies in Europe, a statistical monitoring system has been developed to detect recent clusters or long-term (10 year) time trends. The purpose of this article is to describe the system for the identification and investigation of 10-year time trends, conceived as a ''screening'' tool ultimately leading to the identification of trends which may be due to changing teratogenic factors. METHODS: The EUROCAT database consists of all cases of congenital anomalies including livebirths, fetal deaths from 20 weeks gestational age, and terminations of pregnancy for fetal anomaly. Monitoring of 10-year trends is performed for each registry for each of 96 non-independent EUROCAT congenital anomaly subgroups, while Pan-Europe analysis combines data from all registries. The monitoring results are reviewed, prioritized according to a prioritization strategy, and communicated to registries for investigation. Twenty-one registries covering over 4 million births, from 1999 to 2008, were included in monitoring in 2010. CONCLUSIONS: Significant increasing trends were detected for abdominal wall anomalies, gastroschisis, hypospadias, Trisomy 18 and renal dysplasia in the Pan-Europe analysis while 68 increasing trends were identified in individual registries. A decreasing trend was detected in over one-third of anomaly subgroups in the Pan-Europe analysis, and 16.9% of individual registry tests. Registry preliminary investigations indicated that many trends are due to changes in data quality, ascertainment, screening, or diagnostic methods. Some trends are inevitably chance phenomena related to multiple testing, while others seem to represent real and continuing change needing further investigation and response by regional/national public health authorities. Birth Defects Research (Part A) 91:S31-S43,

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