[Significance of hyper-echogenic yolk sac in first-trimester screening for chromosome aneuploidy]

Recently, the measurement of the thickness and extent of the first-trimester posterior simple embryonic hygroma by vaginal ultrasound has become the most efficient method in the antenatal screening for chromosomal aneuploidies. The sensitivity of the screening is only 75-90%, therefore, the search for other potential (sonographic) markers is needed in order to increase the efficiency. Ultrasound measurement of the echogenicity and the diameter of yolk sac and the thickness of dorso-posterior simple embryonic hygroma was carried out in 3620 first-trimester pregnancies between 9-11 weeks. A total of 105 embryos with simple hygroma of > or = 3 mm and 39 pregnancies with abnormal, hyperechogenic yolk sac of 1.8-4.0 mm in diameter were detected. Cytogenetic analysis through chorionic villi samples revealed chromosomal aneuploidies in 52 cases. In 19 of 3620 pregnancies both hyperechogenic yolk sac and first trimester simple hygroma were present. Each of these 19 pregnancies were chromosomally abnormal. Hyperechogenic yolk sac alone was present in another 20 pregnancies with otherwise normal fetal findings. The authors could not accomplish sonographic identification of the yolk sac in 42 pregnancies. In conclusion, combined presence of hyperechogenic yolk sac plus first-trimester simple hygroma of 3 mm or more in the same pregnancy is highly associated with chromosomal aneuploidy between the 9-11 gestational weeks.