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.