31 week growth ultrasound

Hey! So, we just went for a growth ultrasound (@ 31 weeks)... Everything looked/measured fine (43rd percentile @ approx 3lb 12oz). But... the tech and doctor did find a small pocket of fluid around near her bladder. Could be a cyst or a blockage.

The ultrasound doctor said it could clear up on its own, or it’ll require some monitoring after birth. Is this serious? The dr wasn’t very informative nor reassuring at all, and my OBGYN hasn’t called me yet since this was just a few hours ago.