There is no way. Everything out there is an old wives tale...the only thing we tried before the sonogram was the chinese calendar and both times it was correct.
I know the waiting is rough!! Ultrasounds are pretty much the only way to tell the gender unfortuantely. However, if you look up some old wive's tales, and take gender prediction tests, they are really fun to try to guess the gender until you do find out! If she's 4 months she should be finding out pretty soon!!