Just throwing it out there as something else to contemplate but when you are showing may play a part too. One of my SILs you can tell from about 7 wks and the other I never figure out till she tells us (usually at the 16-20 wks mark). If you look like you might be it might be better to say something than having guessing games going on. I do agree with others though that it just needs to be done with a sensitivity towards those who may be still grieving and that it sounds, to me at least, that your mum is worried about the negative possibilities and wants to have it all cleared so she doesn't get her hopes up. All the best with your pregnancy.