References to Fertility while Breastfeeding

I was reading a bit of this book, Why Zebras Don't Get Ulcers at my BIL's while away last weekend and came across a section about fertility while breast feeding.

Apparently researchers studying hunter/gatherer groups of humans noticed 3-4 years child-spacing for mothers. At first they thought it was due to poor diet but that wasn't true. Finally they realized it was due to the extended, readily available, nursing on demand, done by the mothers of their babies until about 3yrs. It talked more about how prolactin works to prohibit progesterone from functioning properly during the LP which inhibits implantation. It also mentions that the reason BF as contraception fails for some is that Western moms try to feed on a schedule rather than on-demand which compromises the effect of the hormones released during nursing.

Makes me think I might be in for a little bit longer ride if I'm not going to wean....

That said, Jonah is almost 16 months now and recently he has shifted his nursing behavior some. He has cut back a bit and while he will reach for the girls if he wants to nurse he will equally pull my shirt down when he is finished and say "alllll done! allllll done1"


Also, another gal in a group I'm on came across a reference to a greater chance of twins for conceptions while nursing. Something like 12 times more likely to have twins. Evidently it is partly the effect of lower blood calcium levels in nursing moms as well as a higher level of FSH also due to nursing.

(The higher FSH must be our brains yelling at our ovaries over the sound of the prolactin.)