Fluid sac

Dear Dr. I am 5 weeks pregnant after injectible cycle/HCG/IUI. In an ultrasound done yesterday, the dr. identified 3 findings: 1. a gestational sac 2. an enlarged ovary - bigger than the uterus - in his words. 3. a fluid sac between the uterus and the back. i am going for another ultrasound in a week. my question is - what are the risks of this fluid sac, and what treatment is needed to solve this situation? thanks, orit