High volumes of baby boys in sims!

I swear all of my sim families only give birth to boys lately. is this a glitch or totally random? I have 4 different sim families in 4 different games and all have had only boys. One family had 4 boys. the other had two sets of twin boys, my one sims is pregnant with TRIPLET boys and my newest sim is currently pregnant with a boy. what's going on??