My best friend recently was tested and had practically NO estrogen in her system!! She went from pregnant to nursing to pregnant to nursing (total of 4 years). At least the nursing part is very estrogen depleting, not sure about pregnancy.
BTW: she also had a progesterone only birth control (Nuva Ring maybe?) during the last 18 months (nursing) of that 4 years. Her estrogen depletion is also accompanied by (related or not, she's not sure yet) a bunch of other issues.