It has been well documented (I will be happy to pull references if you would like) that 10% of women develop post-partum thyroiditis...I had a run of 3 in 2 months last spring! The time period seems to be within the first year postpartum. People have advocated for prenatal (or hopefully prepregnancy, such as at a well-woman visit) thyroid screening, and then to repeat thyroid testing at 6 weeks postpartum. Definitely family history of thyroid disease is an important reason to screen women. Since I do alot of well-women care and see alot of lactating women, I am constantly doing thyroid tests, and I would say that I diagnose about 1-2 patients per week with thyroid disease. Thyroid disease is the number 1 hormonal problem women develop. Since you may be reading this, ...want to hear my created evolutionary explanation for this prevalence of thyroid disease? Our bodies are not much different than cave-woman times. By the age of 30+, cave women no longer bore children, and thyroid degeneration is a natural way to die. I especially believe this because hypothyroidisn during the peri-menopausal period is incredibly common! This is not a proven theory. Anne Eglash, MD