Combined First-trimester Screening of Trisomy 21 in Women of Different Ages in Southwest Iran

Abstract

Background: There is evidence that the incidence of trisomy 21 has a direct linear relationship with maternal age, and older women are at a higher risk for giving birth to neonates with Down syndrome (DS). Objectives: The present study aimed to evaluate the performance and effectiveness of combined first-trimester screening (FTS) for DS in women of different ages in Southwest Iran. Methods: In this cross-sectional study, FTS was conducted on 7192 pregnant women in the 11th to 13th week of gestational age, referred to the Narges Medical Genetics and Prenatal Diagnosis Laboratory, Ahvaz, Iran. Amniocentesis and cytogenetic analysis were performed in all women with an estimated risk of 1 in 100 and above. Results: The FTS detection rate of DS was 83.3%, with the false positive rates of 2.1% and 13.5% in young women and those over 35 years, respectively. A significant correlation (r = 0.137, P < 0.001) was observed between the high risk of DS (1:100) and maternal age. The high risk of DS was found to be higher in women over 35 years of age than those under 35 years old (6.67% vs. 1.95%). Total DS prevalence was 2.64 per 1000 cases. The prevalence of DS in women under and over 35 years of age was 1.95 and 6.67 per 1000 pregnancies, respectively. Conclusions: First-trimester screening is an effective method for estimating the risk of DS in women under or over 35 years of age. Although an advanced maternal age is associated with a higher prevalence of DS, clinicians should recommend FTS as the first-line screening method regardless of maternal age.