I nursed my first till she stopped on her own around34 weeks in my second pregnancy. I'm 19 weeks now with the third, and second is still nursing. Many, though not all, women find that theirmilk supply decreases and/or changes flavor, so nursling may self wean.
I think the hesitation for many is the possibility of preterm labor. But lately they haven't found any research to confirm that. Right now I'm nursing my 18 mo. I'm around 9 weeks preggo. I haven't had any issues other than a dip in my supply. I'm so hoping she self weans, but there's no end in sight. I might be tandem nursing here soon!