we didnt find out for the first three, but did for ds4 and i am now 38wks preg with no 5, which according to scans is a girl!
for no 1 i wanted a suprise and dp wanted a suprise for no 2 and no 3, by no 4 i wanted to know, so we found out but kept it a secret :)
this time round, no 5 and a girl after 4 boys i was CONVINCED i was having another boy, we werent going to find out and then the sonographer said she had a really good view and did we want to know, dp immediately said yes!
then the poor sonographer spent the rest of the scan saying it REALLY is a girl as we wouldnt believe her
she actually said to us, she isnt allowed to say she is 100% sure, but that she WAS 100% sure! i still booked and had a private scan at 28wks to check, where i saw for myself that she is indeed a girl.
however despite that i havent really bought anything girly (have been given loads) and all the first outfits i have ready, babygrows etc are unisex.
we also have a name picked if she comes out a he, but are struggling with a girls name 
anyhow as i am 38wks we shall find out for sure soon!