Pocket if fluid in my uterus

Today I went to get my first ultrasound at 5 weeks and everything looks good but the nurse said I have a pocket of fluid in my uterus ... she didn’t look concern so I didn’t ask anything... but now it got me thinking... is this normal? I’m suppose to go again in 10 more days for another ultrasound

Anyone have or had the same thing? Should I be worry?