I am a working mom (soon to make whatever sacrifices I must to retire, as I read more and more studies that children don't do as well when the primary caretaker is someone other than a parent) who has used this method of child spacing with great success. I nurse my daughter on demand when I am at home and at night (no getting up for late night feedings, just flip over and go back to sleep!), and pump once during the day at work and so far my periods haven't returned. My daughter is 22 months old and I haven't had a period since 1997! For anyone who is working and wants to use this method, I would recommend combining it with fertility awareness - you can check ccli.org for more info on that - just to make sure, because obviously the chances of fertility returning are greater when you're not with your child day in and day out. The knowledge that constant mother-baby togetherness causes this natural child spacing leads me to greater belief that mothers and baby are biologically designer to be together at all times, and logic tells me (as studies confirm) that if I try to do otherwise, harm comes to both of us. [...]
Update: Jan 2006 - I had 27 months of infertility after each of my first two children and am in month 14 after my third. My gynecologist said I have all but eliminated any chance of breast, ovarian, or endometrial cancer (because I've had only 6 cycles in 8 years) by adopting this time-tested lifestyle.
A woman who follows the standards of natural mothering closely (especially nursing while sleeping) typically receives 20-30 months of postpartum infertility. A more modern-style nurser averages 14 months, decreasing with more separation, limited comfort nursing, and longer nursing intervals.