These two mechanisms help to satisfy the increased demand for calcium during pregnancy. Other physiologic changes during pregnancy that may actually be protective of bone include the third trimester estrogen surge and increased bone-loading due to weight gain. Clearly, there is much to be learned about bone remodeling during pregnancy and why some women become prone to bone loss and even fracture. Lactation and Bone Loss Studies have shown that the majority of women with pregnancy-associated osteoporosis are breastfeeding at the time of diagnosis. Duration of lactation has ranged from one week to seven months.
Bone loss tends to be greatest in skeletal sites with the highest concentration of trabecular bone.
Reductions in bone density by three to five percent at the lumbar spine are common. Two physiologic occurrences may be responsible for bone loss during lactation. First, there is an increased calcium demand from maternal bone. This demand varies from woman to woman based on the amount of breast milk produced and upon the duration of lactation. Secondly, because of elevated prolactin levels, women who breastfeed tend to be in a hypoestrogenic state.