Changes in bone mineral density of the os calcis as measured by quantitative ultrasound during pregnancy and 24 months after delivery

Mechanical Regulation of the Maternal Skeleton during Reproduction and Lactation

PURPOSE OF REVIEW

This review summarizes recently published data on the effects of pregnancy and lactation on bone structure, mechanical properties, and mechano-responsiveness in an effort to elucidate how the balance between the structural and metabolic functions of the skeleton is achieved during these physiological processes.

RECENT FINDINGS

While pregnancy and lactation induce significant changes in bone density and structure to provide calcium for fetal/infant growth, the maternal physiology also comprises several innate compensatory mechanisms that allow for the maintenance of skeletal mechanical integrity. Both clinical and animal studies suggest that pregnancy and lactation lead to adaptations in cortical bone structure to allow for rapid calcium release from the trabecular compartment while maintaining whole bone stiffness and strength. Moreover, extents of lactation-induced bone loss and weaning-induced recovery are highly dependent on a given bone's load-bearing function, resulting in better protection of the mechanical integrity at critical load-bearing sites. The recent discovery of lactation-induced osteocytic perilacunar/canalicular remodeling (PLR) indicates a new means for osteocytes to modulate mineral homeostasis and tissue-level mechanical properties of the maternal skeleton. Furthermore, lactation-induced PLR may also play an important role in maintaining the maternal skeleton's load-bearing capacity by altering osteocyte's microenvironment and modulating the transmission of anabolic mechanical signals to osteocytes. Both clinical and animal studies show that parity and lactation have no adverse, or a positive effect on bone strength later in life. The skeletal effects during pregnancy and lactation reflect an optimized balance between the mechanical and metabolic functions of the skeleton.

Effects of Parity and Breast Feeding Duration on the Risk of Osteoporosis in Postmenopausal Korean Women: A Systematic Review and Meta-Analysis

OBJECTIVES

To summarize the evidence regarding the association of parity and breast feeding duration with the risk of osteoporosis in postmenopausal Korean women. This was because studies have been inconsistent regarding the effect of parity and breast feeding duration on the risk of osteoporosis.

METHODS

A systematic literature search of relevant studies published by December 26, 2018 was conducted in PubMed, EMBASE, the Cochrane Library, CINAHL, RISS, KISS, KMbase, and KoreaMed. Outcome estimates of odds ratio (OR) or standardized mean difference were pooled with fixed or random-effect model. In case of heterogeneity, subgroup analysis was conducted.

RESULTS

Seven cross-sectional studies (with 3,813 subjects) were included in the analysis. OR for osteoporosis was 1.43 (95% confidence interval [CI] = 1.09-1.88, P = 0.010) in postmenopausal women with higher parity compared to those with less parity. Moreover, OR for osteoporosis was 1.93 (95% CI = 1.28-2.93, P = 0.002) in postmenopausal women with longer durations of breast feeding than in those with shorter durations of breast feeding.

CONCLUSIONS

This study revealed that duration of breast feeding increased the risk of osteoporosis in postmenopausal Korean women. More cohort studies with high quality research designs are needed to confirm our results.

Effects of Parity and Breastfeeding Duration on Bone Density in Postmenopausal Women

PURPOSE

This study aimed to identify the effect of parity and breastfeeding duration and the occurrence of lumbar vertebral and femoral neck osteoporosis in Korean postmenopausal women.

METHODS

This study analyzed the data of 1,770 women based on the 2010-2011 results of the Korea National Health and Nutrition Examination Survey. Extracted data concerning bone density included variables known to be associated with osteoporosis. Complex sample multivariate logistic regression analysis was conducted to determine whether parity and breastfeeding duration were associated with osteoporosis in postmenopausal women.

RESULTS

Parity was not associated with postmenopausal osteoporosis in the femoral neck or lumbar vertebrae; however, the risk of femoral neck osteopenia was significantly higher in women with a history of 12-24 months of breastfeeding than in women who breastfed for less than 12 months (odds ratio = 2.12, 95% confidence interval = 1.07-4.21). In women who breastfed for 24 months or longer, the risk of lumbar vertebral osteoporosis was significantly higher than in those who breastfed for less than 12 months (odds ratio = 2.73, 95% confidence interval = 1.18-6.32).

CONCLUSION

Breastfeeding duration may affect the occurrence of lumbar vertebral or femoral neck osteopenia or osteoporosis. Therefore, women who breastfeed for one year or more require education on the risk of bone loss and the need for preventive measures such as adequate calcium intake and physical exercise.

Maternal Mineral and Bone Metabolism During Pregnancy, Lactation, and Post-Weaning Recovery

During pregnancy and lactation, female physiology adapts to meet the added nutritional demands of fetuses and neonates. An average full-term fetus contains ∼30 g calcium, 20 g phosphorus, and 0.8 g magnesium. About 80% of mineral is accreted during the third trimester; calcium transfers at 300-350 mg/day during the final 6 wk. The neonate requires 200 mg calcium daily from milk during the first 6 mo, and 120 mg calcium from milk during the second 6 mo (additional calcium comes from solid foods). Calcium transfers can be more than double and triple these values, respectively, in women who nurse twins and triplets. About 25% of dietary calcium is normally absorbed in healthy adults. Average maternal calcium intakes in American and Canadian women are insufficient to meet the fetal and neonatal calcium requirements if normal efficiency of intestinal calcium absorption is relied upon. However, several adaptations are invoked to meet the fetal and neonatal demands for mineral without requiring increased intakes by the mother. During pregnancy the efficiency of intestinal calcium absorption doubles, whereas during lactation the maternal skeleton is resorbed to provide calcium for milk. This review addresses our current knowledge regarding maternal adaptations in mineral and skeletal homeostasis that occur during pregnancy, lactation, and post-weaning recovery. Also considered are the impacts that these adaptations have on biochemical and hormonal parameters of mineral homeostasis, the consequences for long-term skeletal health, and the presentation and management of disorders of mineral and bone metabolism.

Presentation and management of osteoporosis presenting in association with pregnancy or lactation

In this review, we summarize our current understanding of the pathophysiology of fragility fractures that occur for the first time during pregnancy and lactation, and provide guidance on appropriate investigations and treatment strategies. Most affected women will have had no prior bone density reading, and so the extent of bone loss that may have occurred during pregnancy or lactation is uncertain. During pregnancy, intestinal calcium absorption doubles in order to meet the fetal demand for calcium, but if maternal intake of calcium is insufficient to meet the combined needs of the mother and baby, the maternal skeleton will undergo resorption during the third trimester. During lactation, several hormonal changes, independent of maternal calcium intake, program a 5-10 % loss of trabecular mineral content in order to provide calcium to milk. After weaning the baby, the maternal skeleton is normally restored to its prior mineral content and strength. This physiological bone resorption during reproduction does not normally cause fractures; instead, women who do fracture are more likely to have additional secondary causes of bone loss and fragility. Transient osteoporosis of the hip may affect one or both femoral heads during pregnancy but it involves localized edema and not skeletal resorption. Case reports have described the use of calcitonin, bisphosphonates, strontium ranelate, teriparatide, vertebroplasty, and kyphoplasty to treat post-partum vertebral fractures. However, the need for such treatments is uncertain given that a progressive increase in bone mass subsequently occurs in most women who present with a fracture during pregnancy or lactation.

Osteoporosis presenting in pregnancy, puerperium, and lactation

PURPOSE OF REVIEW

To describe our current state of knowledge about the pathophysiology, incidence, and treatment of osteoporosis that presents during pregnancy, puerperium, and lactation.

RECENT FINDINGS

When vertebral fractures occur in pregnant or lactating women, it is usually unknown whether the skeleton was normal before pregnancy. Maternal adaptations increase bone resorption modestly during pregnancy but markedly during lactation. The net bone loss may occasionally precipitate fractures, especially in women who have underlying low bone mass or skeletal fragility prior to pregnancy. Bone mass and strength are normally restored postweaning. Transient osteoporosis of the hip is a sporadic disorder localized to one or both femoral heads; it is not due to generalized skeletal resorption. Anecdotal reports have used bisphosphonates, strontium ranelate, teriparatide, or vertebroplasty/kyphoplasty to treat postpartum vertebral fractures, but it is unclear whether these therapies had any added benefit over the spontaneous skeletal recovery that normally occurs after weaning.

SUMMARY

These relatively rare fragility fractures result from multifactorial causes, including skeletal disorders that precede pregnancy, and structural and metabolic stresses that can compromise skeletal strength during pregnancy and lactation. Further study is needed to determine when pharmacological or surgical therapy is warranted instead of conservative or expectant management.