If you haven't done the wedding ring thing, then you need a piece of thread (any cheap sewing kit), and tie a wedding ring (has to be a wedding ring) onto the thread. Then you hold the ring over your bump by the thread (thread should be long enough - maybe 8inches) and you dip the ring down towards your tummy once (because it's your firstborn). You don't actually touch the tummy with the ring, just dip the ring towards the tummy.
If it's a boy, once you've dipped the ring on the thread and just hold it, the ring will move in a straight forwards/backwards motion.
If it's a girl, it will move in a circular motion.
I think you're supposed to get another mother to do this, so your own mother for example.
It's actually freaky so see the ring in some sort of magnetic field. This test on me indicated a girl every time (but not wanting to get my hopes up I called bullshit on it), but yes it was correct.
It's a fun way to spend time.
I also spent time reading rune stones my mother I had gotten. It's so exciting and God so exciting!
Let us know how the ring goes.