Enlarged Cisterna magna detected during Congenital Anomaly scan

Hi,

My name is Jade, I am 30 years old and is on my 32nd week of  pregnancy. This is my first pregnancy. I had my CAS on my 20th week and they found a choroid plexus cyst on the left part of the brain. My OB-Sonologist recommended that we do a follow up scan every 2 weeks to monitor the cyst. On my 30th week, the choroid plexus cyst was gone but she found that the baby has an enlarged cisterna magna instead in the left. There are no other anomalies found. I also underwent Biophysical Score for my baby and the same result was found - enlarged cisterna magna. I tried to check the internet what this means because this was not fully discussed by my OB-Gynecologist. I am now worried because most explanations I read about enlarged cisterna magna relates it to high risk of Trisomy 18, 13 and Hydrocephalus and a high risk of fetal mortality. Ultrasound result showed that I am conceiving a baby boy. I also had premature contractions recently so I had to be in complete bed rest.

Can you please enlighten me about this. What are the chances that my child would survive, or would be normal?
Thanks a lot.

Worried mom,
Jade