Influence of the estimation of gestational age by using different ultrasound examination during second pregnancy trimester for Down syndrome screening

Abstract

Objective To evaluate the influence of gestational age by using different ultrasound examination during second pregnancy trimester for Down syndrome (DS) screening. Methods A total of 5 934 second trimester pregnancies who received DS screening between January and December 2012 at prenatal diagnosis center of West China Second University Hospital, Sichuan University were included into this study. They were divided into two groups according to different methods of estimation of gestational age, crown-rump length group (n=2 967, received ultrasound at 8-14 weeks) and biparietal diameter group (n=2 967, received ultrasound at 14-20 weeks). The positive rate and screening efficiency of DS screening were compared between biparietal diameter group and crown-rump length group. There were no significant differences between two groups in the aspects of age and weight (P>0.05). Results ①Crown-rump length group received DS screening mainly at 15-17 weeks, and biparietal diameter group received DS screening mainly at 15-20 weeks. ②The positive rate of biparietal diameter group was significantly higher than that in crown-rump length group (9.8% vs 6.2%), with significant difference (χ2=26.641, P 0.05). Conclusions The estimation of gestation age for DS screening using crown-rump length at 8-14 weeks of pregnancy was better than the estimation of gestation age by biparietal diameter at 14-20 weeks. Key words: Down syndrome; Pregnancy trimester, second; Gestational age; Biparietal diameter; Crown-rump length