Diagnosis of Cystic Hygroma
Doctors usually diagnose cystic hygromas when the fetus is still in the womb, often during a routine abdominal ultrasound.

Doctors may also detect it during a blood test carried out at 15 to 20 weeks. If the blood test shows high levels of alpha-fetoproteins, it might indicate a possible cystic hygroma.

Ultrasound images may indicate the possible location and size of a cystic hygroma, but doctors will require more information. They will want to know the depth and severity of the growth and if there are any obstructions, including those that could indicate breathing problems.

Doctors may do additional tests, including:

Transvaginal ultrasound: A transvaginal ultrasound can take better images of the cystic hygroma without other organs in the way.
Fast spin magnetic resonance imaging (MRI): A fast spin MRI can provide a clear image and more details about the cystic hygroma. Unfortunately, it is an expensive test.

Amniocentesis: During amniocentesis, a doctor will collect amniotic fluid through a special needle, then test it for chromosomal abnormalities.
A doctor will use computed tomography (CT) scans, X-rays, and ultrasounds to make a diagnosis if they find a cystic hygroma after a child is born.