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Objectives: We evaluated the performance of first trimester screening for Down syndrome in women less than 35 years of age (study group) and in women aged 35 years or more (control group) in an unselected low-risk population., Methods: The study group comprised a total of 63,945 women who participated in the first trimester combined screening in public health care in Finland during the study period of 1 May 2002 to 31 December 2008. Women at the age of 35 or more (n = 13,004) were controls. Prevalence of Down syndrome, detection rate, false positive rate and number of invasive procedures needed to detect a single case of Down syndrome were analyzed in both groups., Results: The overall prevalence of Down syndrome (n = 73) in the study group was 1:876. The number of detected cases was 54. The detection rate was 74.0% with a false positive rate of 2.8%. Number of invasive procedures needed to detect a single case of Down syndrome was 33. In the control group, the detection rate was 87.0% with a false positive rate of 11.9%. The number of invasive procedures needed to detect a single case of Down syndrome was 15. The differences in detection rate and false positive rate were significant, P < 0.012, P < 0.001, respectively., Conclusion: The overall detection rate given for the entire population is an overestimate for a woman younger than the age of 35, which should be taken into consideration when counselling women of that age., (© 2012 Blackwell Publishing Ltd.)

Objective: To evaluate the performance of first-trimester combined screening in 5-year periods according to maternal age in a low-risk population., Design: A prospective study., Setting: Multicenter study in Finland., Population: A total of 76949 voluntary women with singleton pregnancies participated in first-trimester combined screening in public healthcare between 1 May 2002 and 31 December 2008., Methods: The serum samples were analyzed using the PerkinElmer AutoDELFIA® time-resolved fluoroimmunoassay kit for the measurement of pregnancy-associated plasma protein-A and free beta-human chorionic gonadotropin. Nuchal translucency was measured by trained personnel (midwives or physicians) in a university or central hospital., Main Outcome Measures: Performance, detection rate, false positive rate and the number of invasive procedures needed to detect a single case of Down's syndrome were analyzed., Results: There was a direct connection between maternal age and the prevalence of Down's syndrome with a low prevalence in young women being 1:1 193 in the 25-29 age group and 1:150 in the 35-39 age group. Consequently, for a fixed false positive rate of 5%, the number of invasive procedures needed to detect one case of Down's syndrome is higher in younger women to achieve the same detection rate., Conclusions: In combined first trimester screening the risk for Down's syndrome is individual, varying with maternal age. This should be taken into consideration when counseling women., (© 2011 The Authors Acta Obstetricia et Gynecologica Scandinavica© 2011 Nordic Federation of Societies of Obstetrics and Gynecology.)

The characteristics of the Finnish parturient have changed in recent years. The mean age of mothers at first delivery is now 29.3 years and the number of women > 35 years of age has increased to 19%. This shift has led to an increase in the prevalence of Down's syndrome. Between 1 January 2002 and 31 December 2006, there were 795 cases of Down's syndrome (27/10,000) in the Finnish Register of Congenital Malformations. The distribution of Down's syndrome in terminated pregnancies and newborns was analyzed in 5-year periods based on maternal age. The distribution of Down's syndrome cases in younger women (< 35 years) and in older women (> or =35 years) at the time of delivery was compared. The majority of new Down's syndrome cases occurred in the group having older women (61.1%), even though 35 years is the arbitrary threshold.