Thank you for putting up your problem to Healcare Magic!
The mass does not seem to be a malignant one but free fluid in POD is ominous.
has fairly good sensitivity but MRI
is needed for more clarity in your case.
MRI is safe investigation in pregnancy
Surgery if required is safe in second trimester.
Your Gynecologist would be in a better position to guide you after the MRI findings are at hand.
I hope this information would be both informative and helpful for you