my dr checked me for twins with my ds2 b/c i was measuring larger than i should've been. but no twins, just a large uterus. it was my second baby after all and my ds1 was only 8 months when i became pregnant again. i'd have to say though with ds1 i was hoping for twins, ds2 not so much and this time disappointed to find out it wasn't twins. lol guess i'm a freak for wanting them?
and to one of the pp it's not just hereditary, in fact 65% of pregnancies begin as twins but one gets "lost". and identical twins are NOT hereditary at all, it's fraternal twins that are. identicals just kinda happen, but it can be hereditary to drop more than one egg at a time. not hereditary for your eggs to just randomly split, that's just a miracle of nature.
anyhow i wouldn't worry about it yet...i have shown earlier with each pregnancy. and twins are just such a blessing anyhow.