J Musculoskel Neuron Interact 2001; 1(4):347-355 Perspective Article Skeletal adaptations during mammalian reproduction

Remarkable changes occur in the mammalian skeleton prior to, during and after the reproductive cycle. Skeletal changes occur with ovarian maturation and initiation of menses and estrus in adolescence, which may result in a greater accumulation of skeletal mineral in the female vs the male skeleton. There is also some evidence to suggest an excess skeletal mass in young female experimental animals. In early pregnancy, growth, modeling and perhaps suppressed remodeling promote the accumulation of calcium. Some changes may also occur with the transition from pituitary to placental control of the pregnancy. In later pregnancy, an increase in bone turnover appears to coincide with fetal skeletal mineralization. Rapid and important changes occur in the skeleton and mineral metabolism in the transition from pregnancy to lactation as the mammary gland rather than the uterus draws on the maternal calcium stores. Lactational demands are met at least partially by a temporary demineralization of the skeleton, which is associated with increased bone modeling and remodeling. Endochondral growth almost ceases during lactation, but envelope-specific bone modeling and remodeling are greatly increased. This is generally associated with a loss of skeletal mass and density, more apparent at sites with less of a mechanical role (e.g. central metaphysis regions and the endocortical envelope). The post-lactational period is profoundly anabolic with substantial increases in bone formation, but blunted resorption at almost all skeletal envelopes. Skeletal mass is increased during this period and it is associated with improved skeletal mechanical properties. There are several important observations. 1) The nulliparous anima