Post partum thyroid dysfunction is common especially in women with Hashimoto's thyroid inflammation. This can express itself as mild depressions through to full paranoid delusions and psychotic behavior. With the help of anti-depressants and thyroid most people can be brought out of this quite quickly. Fortunately response is often rapid, within a week to thyroid hormone and anti-depressants.
During the pregnancy the demands for thyroid hormone and iodine are more than normal. The placenta also puts out a hormone to make the thyroid work more. So when the stress of the pregnancy is removed the thyroid may end up partially burned out. So just when the mother needs to cope well (needs thyroid hormone) she is left with a worn out thyroid.
Adequate thyroid hormone is essential for initiating breast feeding and this is where that problem comes from. All mammals need thyroid to initiate breast feeding and it is most extreme in the cat. During the immediate post partum period the cat totally empties its thyroid in order to start breast feeding. (1) As well thyroid hormone initiates and controls the last enzymatic process in the breast to make milk.
The thyroid hormone and thyroid gland together with iodine are the most important factors by far for completion of a normal pregnancy and normal baby. Iodine is put into the mother's milk by the lactating breast to levels that are 30 times the levels in the mother's blood. Iodine still has important functions in the child's brain development after birth. Most likely the iodine in the mother's milk is the same function as the iodine in pregnancy which is ensure that the natural death of cells occurs (apoptois). The death of many cells in the brain and elsewhere during development is an important function. Newer evolutionary parts of the brain replace older ones. Because there is limited space in the skull some cells have to die off to make room for the more evolutionary modern cells. It has been estimated that about 80 percent of the brain tissue is replaced during development in this manner.
There is an increased need for thyroid hormone and iodine during pregnancy. Thus each pregnancy is a load on the thyroid function which not every women's thyroid gland carries out adequately. As thyroid is important for adolescence, normal menstruation, pregnancies and menopause it is not surprising the females have a much higher incidence of thyroid dysfunction.
So I feel poor milk production in women with a history of thyroid dysfunction is likely related to low blood levels of thyroid hormone. As breast feeding is so important to the child and mother it seems important to check this out at the time.
It is likely that if thyroid hormone is given to a mother with breast feeding problems the problems would disappear quickly within a week.
(1) Pitt-Rivers R, Tata JR. Thyroid hormones. 1st ed. London: Pergamon, 1959. page 86-88.
(2) Moon RC. Influence of graded thyroxine levels on mammary gland growth. Amer J Physiol 1962; 203:942-946.
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See Increasing breast milk production
These are personal opinions. Please discuss any ideas you get with your physician.