I didn't know I had fibroids until my first US. The caused me lots of pain during the pregnancy and I had to go for monthly US for various reasons, but one was to make sure that they weren't harming the baby in any way. The good news is that they didn't harm his development and everything was fine.
if the doctor sees this he will warn u. U run a higher risk of M/c's but i do know some woment who have gone thru pregnancy with just period pains durring and have happy healthy babies. Call ur doctor tell them u are concerned.