screening of fetal chromosome aneuploidies in the first and second trimester of 125,170 iranian pregnant women

background : aneuploidy is one of the main causes of congenital anomalies, mental and physical disabilities, in new-borns. the aim of this study was to determine various chromosomal aneuploidies in the first and second trimester screening of pregnant women, in iran. methods : a descriptive retrospective study was conducted on 125,170 pregnant women referred to a major referral medical diagnostic laboratory (niloo laboratory, tehran) for prenatal screening tests (2010-2013). patients were di-vided into 3 groups: first trimester screening (fts), second trimester screening (sts), and combined screening groups. in positive and borderline cases, and amniocentesis and cytogenetic analysis were carried out. results : total prevalence of aneuploidy in 125,170 pregnant women was one in 491, (detection rate=82.7% for down syndrome). the dr for ds in three groups was as follow: 87.5% for fts (25783 women), 80.9% for sts (91345 women), and 94.7% for combined tests (8042 women). total number of cases with edward's syndrome was 18, patau's syndrome six, klinefelter syndrome six, triploidy three, and cri-du-chat syndrome one. conclusion : the present study shows the frequency of aneuploidy in the first and second trimester screenings in a major medical laboratory in tehran. the prevalence of aneuploidies grows with increased maternal age. the rate of aneuploidy in first trimester is higher than second.