Free pelvic fluid on US but heartbeat seen

Charlotte • Honeymoon baby in situ!
Anyone any ideas as to what pelvis fluid is, is caused by and what needs to happen next? US lady said my pregnancy was a good viable pregnancy and didn't seem to concerned but my report does reference the free pelvic fluid.... Will it affect my baby? Heartbeat etc. Was all normal but I'm totally confused... I've posted a picture of said fluid.... Help please!!