What ultrasound finding is most commonly associated with Turner's Syndrome?

In the context of Turner's Syndrome, cystic hygroma is the ultrasound finding most commonly associated with this condition. Cystic hygroma is a fluid-filled sac that can develop in the fetal neck and is characterized by the presence of lymphatic fluid. It occurs due to improper development of the lymphatic system and is frequently observed in cases of chromosomal abnormalities, with Turner's Syndrome being one of the most notable examples.

The presence of cystic hygroma can be significant in prenatal screening, as it has been linked not only to Turner's Syndrome but also to other genetic disorders. The finding often raises suspicion for potential anomalies and may prompt further evaluation and testing.

In contrast, while congenital heart defects can occur in individuals with Turner's Syndrome, they are not as uniquely characteristic or frequent in the prenatal setting. Hydrops fetalis may be observed in a variety of conditions, including rare cases of Turner's Syndrome, but it is not a defining feature. Meconium ileus is more associated with cystic fibrosis and does not relate to Turner's Syndrome. Thus, cystic hygroma stands out as the most characteristic ultrasound finding for Turner's Syndrome, making it the best choice in this scenario.