Another notable number is that I was initially planning on only breastfeeding my daughter for 3 months until I brought this up with her pediatrician earlier this week. For some reason, when I was pregnant, many of my friends told me that they only breastfed their children for 3 months, some did shorter spans and a very slim few did longer spans. So when I told the pediatrician that I was planning to wean my daughter in about a month, I was surprised when she told me that I should do 6 - 12 months of breastfeeding at the minimum. I think part of the reason I was so surprised by this is that it seems to me like everyone else breastfeeds for only 3 months and the minimum is supposed to be double or quadruple that amount of time.
So I went home to do some research. There were many benefits that I already knew were associated with breastfeeding: boosting baby's immune system, reduced risk of SIDS, reduced risk of postpartum depression for mom, etc. My doctor told me that most of these benefits aren't fully realized unless baby receives breast milk for 6 months and that information is subsequently backed up but the AAP:
How long should I breastfeed my baby?
The AAP recommends that babies be exclusively breastfed for about the first 6 months of life. This means your baby needs no additional foods (except Vitamin D) or fluids unless medically indicated. Babies should continue to breastfeed for a year and for as long as is mutually desired by the mother and baby. Breastfeeding should be supported by your physician for as long as it is the right choice for you and your baby.
It's also backed up again here by LLL: