They do say that if it sounds like a train it's a boy and if like a galloping horse a girl. I was at the maternity unit Sat night and I mentioned something about my bump being a girl and the MW said 'yeah, definite girl in there, listen to that horse'! BUT I wouldn't take it as gospel, early on I thought the heartbeat sounded more like a train! Another general observation is that girls heartbeats can be faster than boys - Kayla's (my bump) was between 140-158 while I was at the hospital x