i had this with all my pregnancys and the first 2 were not picked up until they broke my waters with the c sections.
just this time round with DS3 they noticed i was measuring ahead again saw they may of been a tad too much fluids so went for a growth scan.
DS3 was measured to be average and fine, but fluids were at like 28 and 29! but as my c section was less than a week away it was fine to continue.
day of c section he had decided he was coming ready or not lol, (no suprise i was ready to burst with baby and fluids!).
DS1 was 7lb14oz and 49cm long, DS2 was 8lb12 and a half oz, 52cm long, and DS3 was 6lb 15oz and 46cm long! my ob said some women's placentas just make more fluids and not to worry myself (but of course i did i thought they could pop at any second lol). its funny hearing all that water hit the floor it makes a huge splash on the floor lol