Pregnancy-Related Bone Mineral and Microarchitecture Changes in Women Aged 30 to 45 Years

Bone Metabolism, Bone Mass, and Bone Structure During Pregnancy and Lactation: Normal Physiology and Pregnancy and Lactation-Associated Osteoporosis

This article reviews bone metabolism, bone mass, and bone structure changes expected during and after pregnancy and lactation, as well as the condition of pregnancy and lactation-associated osteoporosis (PLO)-a presentation with fragility fracture(s) in the context of these physiologic changes. Clinical implications of physiologic bone changes will be addressed, as will specific management considerations that apply to premenopausal women with PLO.

Lumbar spine bone mineral density in women breastfeeding for a period of 4 to 6 months: systematic review and meta-analysis

BACKGROUND

During the breastfeeding period, important transient changes in calcium homeostasis are verified in the maternal skeleton, to meet the demand for calcium for breastmilk production. The literature is inconclusive regarding the causes and percentages of involvement of bone densitometry resulting from exclusive breastfeeding (4 to 6 months).

METHODS

This article aims to systematically review the literature, to determine the occurrence, intensity, and factors involved in alterations in maternal bone mineral density (BMD), during a period of 4 to 6 months of exclusive breastfeeding. The search descriptors "woman", "breastfeeding", "human milk", and "bone mineral density" were used in the electronic databases of the Virtual Health Library, Scielo (Scientific Electronic Library Online), CAPES Periodicals Portal, LILACS, Embase, PubMed/Medline, Cochrane, Scopus, and Web of Science in June 2023. Inclusion criteria for breastfeedingmothers were; aged to 40 years, primigravida, exclusively breastfeeding, with BMD assessments using dual-energy X-ray absorptiometry (DXA), with values expressed at baseline and from 4 to 6 months postpartum. The Jadad scale, Newcastle-Ottawa Scale, and Oxford Centre for Evidence-based Medicine - levels of evidence were adopted to assess the quality of the studies. For the meta-analytical study, statistical calculations were performed.

RESULTS

Initially, 381 articles were found using the search strategy and 26 were read in full. After risk of bias analysis, 16 articles remained in the systematic review and four were included in the meta-analysis. The studies showed a reduction in bone mass in the lumbar spine in the first months postpartum (4 - 6 months), when compared with a longer period of breastfeeding (12-18 months). The breastfeeding group presented a greater impact in the meta-analysis than the control group (non-breastfeeding, pregnant, or immediate postpartum), with a reduction in BMD in the lumbar spine of -0.18 g/cm2 (-0.36, -0.01 g/cm2); 95% Confidence Interval, on a scale from 0 to 10.

CONCLUSIONS

Our results demonstrated a transitory reduction in bone densitometry of the lumbar spine during exclusive breastfeeding for 4 to 6 months, which was gradually restored later in the postpartum period. More prospective studies are needed to better understand the topic.

TRIAL REGISTRATION

PROSPERO platform (nº CRD42021279199), November 12th, 2021.

The correlation between transient osteoporosis of the hip and pregnancy: A review

Transient osteoporosis of the hip is indubitably a comparatively infrequent entity affecting both men and women worldwide. Its occurrence in the course of pregnancy, specifically in the third trimester, and lactation are of paramount concernment. The exact association between transient hip osteoporosis and pregnancy is precarious. Etiology and potential pathophysiological mechanisms behind this correlation are still to be utterly defined. Magnetic resonance imaging is highly regarded as the gold standard imaging method for assiduous assessment of this disorder. Physicians of copious medical specialties should practice scrupulous techniques for early and pertinent diagnosis when pregnant women are presented with persistent hip pain, as differential diagnosis with femoral head avascular necrosis can be exceedingly arduous. Treatment is predominantly conservative with protected weight-bearing and analgesic medication in the first line of management. In terms of prognosis, the disease ordinarily resolves spontaneously after a few months. Further research is required in order to elucidate the ambiguity surrounding the establishment of globally approved diagnosis and treatment guidelines for pregnancy-associated transient hip osteoporosis. This paper aims to accentuate the significance of this particular disorder by providing a succinct review of the existing literature, augmenting clinicians' knowledge about the features of pregnancy-related transient proximal femur osteoporosis.

Gender Disparities in Osteoporosis Knowledge, Health Beliefs and Preventive Behaviors in Najran City, Saudi Arabia

Osteoporosis is a chronic bone disease affecting both men and women, but it is more prevalent in women. Promoting a healthy lifestyle among adults, particularly women, is crucial in preventing and reducing the osteoporosis impact. This study aimed to compare the osteoporosis knowledge, health beliefs and preventive behaviors among adult male and female in Najran city Saudi Arabia. This cross-sectional study was performed on 516 males and 581 females in Najran City, Saudi Arabia, from January to April 2023. The data collection instrument is a self-reported online questionnaire consisting of basic data, the Osteoporosis Preventive Behavior (OPB) scale, the osteoporosis knowledge assessment tool, and the osteoporosis health belief scale. The results revealed that male participants had a higher OPB (26.70) than females (20.32). However, females have a higher knowledge (10.71), perceive themselves as more susceptible to osteoporosis (20.34) and had higher exercise barriers (20.11) compared to males (9.97, 18.79 and 19.20, respectively). Statistically significant correlations (p < 0.001) were observed between OPB, osteoporosis knowledge (r = 0.26), perceived susceptibility (r = 0.33), severity (r = 0.53), exercise (r = 0.54) and calcium (r = 0.33) benefits, exercise (r = 0.40) and calcium (r = 0.81) barriers and health motivation (r = 0.37). The study concluded significant disparities between males and females regarding osteoporosis-related knowledge, preventive behaviors, perceived susceptibility, severity, and exercise perceived barriers. The results suggest gender-based educational interventions to enhance OPB by addressing osteoporosis-related knowledge, perceived susceptibility, seriousness, benefits, and health motivation.

Bone Microarchitecture and Strength Changes During Teriparatide and Zoledronic Acid Treatment in a Patient with Pregnancy and Lactation-Associated Osteoporosis with Multiple Vertebral Fractures

Pregnancy- and lactation-associated osteoporosis (PLO) is a rare form of osteoporosis, of which the pathogenesis and best treatment options are unclear. In this report, we describe the case of a 34-year old woman diagnosed with severe osteoporosis and multiple vertebral fractures after her first pregnancy, who was subsequently treated with teriparatide (TPTD) and zoledronic acid (ZA). We describe the clinical features, imaging examination, and genetic analysis. Substantial improvements were observed in areal and volumetric bone mineral density (BMD), microarchitecture, and strength between 7 and 40 months postpartum as assessed by dual-energy X-ray absorptiometry at the total hip and spine and by high-resolution peripheral quantitative CT at the distal radius and tibiae. At the hip, spine, and distal radius, these improvements were mainly enabled by treatment with TPTD and ZA, while at the distal tibiae, physiological recovery and postpartum physiotherapy due to leg pain after stumbling may have played a major role. Additionally, the findings show that, despite the improvements, BMD, microarchitecture, and strength remained severely impaired in comparison with healthy age- and gender-matched controls at 40 months postpartum. Genetic analysis showed no monogenic cause for osteoporosis, and it is suggested that PLO in this woman could have a polygenic origin with possible susceptibility based on familiar occurrence of osteoporosis.

"Pregnancy and Lactation Associated Osteoporosis"

Pregnancy-associated osteoporosis (PAO) is a rare condition of skeletal fragility affecting women in pregnancy or the postpartum period. During normal pregnancy and lactation, substantial changes in calcium metabolism and skeletal physiology occur in order to meet the demands of the developing foetus. Whilst these adaptations are reversible and generally of no clinical consequence for the mother, a small number of women will develop osteoporosis and suffer fragility fractures. Vertebral fractures occur most commonly in PAO and are often multiple. Due to the rarity of PAO, systematic study to date has been limited. Aetiology is poorly understood, but traditional osteoporosis risk factors and genetic factors are likely to play a role. A small number of cases may be due to an underlying metabolic bone disorder or monogenic condition. Management of PAO is challenging, due both to a poor evidence base and the fact that spontaneous improvement in BMD is known to occur once pregnancy and lactation are complete. Bisphosphonates, denosumab and teriparatide have all been used in individual patients, but the data supporting their use are currently limited.

Low pre-pregnant body mass index is a risk factor for the decrease of postpartum bone mineral density in systemic lupus erythematosus patients received glucocorticoid therapy

OBJECTIVES

This study investigated postpartum bone mineral density (BMD) in patients with systemic lupus erythematosus (SLE) receiving long-term glucocorticoid (GC) therapy, assessed risk factors for decreased postpartum BMD, and evaluated change of BMD after postpartum initiation or restarting of osteoporosis drugs.

METHODS

We retrospectively examined 30 SLE patients who gave birth and 31 non-pregnant SLE patients. In the postpartum SLE patients, BMD was measured after delivery and 1 year later. Multivariate analyses were performed to assess risk factors for decreased BMD in postpartum SLE patients.

RESULTS

Patient age at pregnancy was 34.5 ± 4.5 years, and SLE duration was 9.7 ± 6.0 years. The mean prednisolone dose was 9.7 ± 3.2 mg/day. Body mass index (BMI) was 21.6 ± 2.2 kg/m², with 13 women (43%) experiencing their first delivery. Postpartum BMD was 1.080 ± 0.120 g/cm² in the lumbar spine and 0.834 ± 0.109 g/cm² in the total hip. Bone loss occurred in six patients (21%) in the lumbar spine and 11 patients (37%) in the total hip. Postpartum lumbar spine BMD was significantly reduced compared to that in the non-pregnant group (1.143 ± 0.120 g/cm², p = 0.048). Multivariate analysis identified gestational age and low BMI before pregnancy as risk factors for hip bone loss.

CONCLUSION

Postpartum BMD significantly decrease in SLE patients receiving long-term GC, and low BMI before pregnancy was a risk factor for the decrease. Preconception care to prevent osteoporosis and that regularly monitors BMD after delivery are needed.

Effects of Vitamin D on Fertility, Pregnancy and Polycystic Ovary Syndrome-A Review

Polycystic ovary syndrome (PCOS) is one of the most common endocrine reproductive disorders in women. Vitamin D deficiency is also quite common in this condition. The degree of vitamin D deficiency correlates with the severity of PCOS. Both male and female vitamin D levels play a role in fertility and affect the outcomes of in vitro fertilization (IVF). Moreover, fertility and IVF indicators are improved by vitamin D not only in healthy women but in those diagnosed with PCOS. Both vitamin D deficiency and PCOS increase pregnancy-related complications. Vitamin D supplementation and optimal vitamin D levels decrease both maternal and fetal risk for complications and adverse events. Furthermore, vitamin D supplementation may ameliorate or even prevent pregnancy-related reversible bone loss in mothers. This review emphasizes the roles of vitamin D deficiency and vitamin D supplementation and their correlation with PCOS regarding reproductive health.

The influence of lactation and its duration on bone mineral density in pregnancy and postpartum: A systematic review with meta-analysis

BACKGROUND

There is a plethora of research on the association of parity and duration of lactation with bone mineral density (BMD) during and after pregnancy. However, there are no consensus conclusions on the impact of the duration of lactation on BMD.

AIMS

The aim of this study was to examine the effect of pregnancy, and the duration of lactation on BMD during pregnancy, postpartum phase and 12 months post-delivery.

METHODS

The search terms 'parity' 'lactation' 'BMD' were searched for using PubMed, CINAHL, SCOPUS and EMBASE databases in English language. Two independent reviewers assessed the quality of the included studies using Critical Appraisal Skills Program (CASP) appraisal tool and extracted data on BMD (g/cm²) in Excel. A meta-analysis was conducted with a random effect model using Cochrane Review Manager (Rev 5.4) to analyse the outcome. Heterogeneity was assessed with Chi Squared and I² test. The duration of lactation was grouped into short lactation duration (SLD), ≤4 months and longer lactation duration (LLD) > 6 months.

RESULTS

Twenty-one studies were included in this review with four studies included in the meta-analysis. BMD reduced during pregnancy and lactation. Recovery and net gains in BMD followed weaning. However, at 12 months postpartum, women in the LLD group had significant losses at the lumbar spine while those in the SLD recovered BMD. Between the SLD and LLD groups, the change in BMD was not significant 0.48 g/cm² (95% CI -0.14, 1.10, p = 0.13). BMD losses were greater in primiparous women than multiparous women.

CONCLUSION

Women who breastfed for >6 months had significantly reduced BMD. However, compared to women that breastfed for a ≤4 months there was no significant change in BMD. Further investigation is needed to clarify the association between lactation and BMD in a postpartum population in those women extending breastfeeding beyond one year.

Bone turnover in pregnancy, measured by urinary CTX, is influenced by vitamin D supplementation and is associated with maternal bone health: findings from the Maternal Vitamin D Osteoporosis Study (MAVIDOS) trial

BACKGROUND

The pattern of change in maternal bone turnover throughout pregnancy is poorly characterized.

OBJECTIVES

We investigated changes across pregnancy in a marker of maternal bone resorption, urinary C-terminal telopeptide of type I collagen (CTX), the influence of gestational vitamin D supplementation, and associations between CTX and maternal postnatal bone indices.

METHODS

MAVIDOS (the Maternal Vitamin D Osteoporosis Study) is a randomized, double-blind, placebo-controlled trial of 1000 IU cholecalciferol/d compared with placebo from 14 weeks of gestation to birth. Maternal second-void urinary α- and β-CTX were measured (ELISA) at 14 and 34 weeks of gestation; DXA was performed within 2 wk postpartum. The Mann-Whitney Rank Sum test, Spearman's rank correlation, and linear regression were used to compare median CTX values within and between groups from early to late pregnancy, and associations with maternal bone outcomes.

RESULTS

In total, 372 women had CTX and 25-hydroxyvitamin D [25(OH)D] measured in early and late pregnancy. CTX at 14 and 34 weeks of gestation were correlated in both placebo (r = 0.31) and cholecalciferol (r = 0.45) groups (P < 0.0001). Median CTX increased from 14 to 34 weeks of gestation in both groups (n = 372 total) [placebo (n = 188): from 223.6 to 449.7 μg/mmol creatinine; cholecalciferol (n = 184): from 222.3 to 419.3 μg/mmol creatinine; P = 0.03 for placebo compared with cholecalciferol difference in CTX at 34 weeks of gestation]. The conditional mean ± SD increase in CTX [z-score (SD)] from early to late pregnancy was greater in the placebo group (n = 188) than in the cholecalciferol group (n = 184) (placebo: 0.16 ± 0.92; cholecalciferol: -0.16 ± 1.06; P-difference < 0.01). Higher CTX at 34 weeks of gestation was associated, similarly in both groups, with lower maternal total hip and lumbar spine bone mineral content and bone mineral density (BMD) (e.g., lumbar spine BMD: β = -0.02 g · cm-2 · SD-1 increase in CTX; 95% CI: -0.027, -0.002 g · cm-2 · SD-1; P = 0.02, n = 283).

CONCLUSIONS

Maternal urinary CTX, a bone resorption marker, rises through pregnancy, although to a lesser degree with gestational cholecalciferol supplementation, and is inversely associated with maternal bone mass postpartum.This trial was registered at www.isrctn.com as ISRCTN 82927713 and eudract.ema.europa.eu as EudraCT 2007-001716-23.

Maternal bone adaptation to mechanical loading during pregnancy, lactation, and post-weaning recovery

The maternal skeleton undergoes dramatic bone loss during pregnancy and lactation, and substantial bone recovery post-weaning. The structural adaptations of maternal bone during reproduction and lactation exert a better protection of the mechanical integrity at the critical load-bearing sites, suggesting the importance of physiological load-bearing in regulating reproduction-induced skeletal alterations. Although it is suggested that physical exercise during pregnancy and breastfeeding improves women's physical and psychological well-being, its effects on maternal bone health remain unclear. Therefore, the objective of this study was to investigate the maternal bone adaptations to external mechanical loading during pregnancy, lactation, and post-weaning recovery. By utilizing an in vivo dynamic tibial loading protocol in a rat model, we demonstrated improved maternal cortical bone structure in response to dynamic loading at tibial midshaft, regardless of reproductive status. Notably, despite the minimal loading responses detected in the trabecular bone in virgins, rat bone during lactation experienced enhanced mechano-responsiveness in both trabecular and cortical bone compartments when compared to rats at other reproductive stages or age-matched virgins. Furthermore, our study showed that the lactation-induced elevation in osteocyte peri-lacunar/canalicular remodeling (PLR) activities led to enlarged osteocyte lacunae. This may result in alterations in interstitial fluid flow-mediated mechanical stimulation on osteocytes and an elevation in solute transport through the lacunar-canalicular system (LCS) during high-frequency dynamic loading, thus enhancing mechano-responsiveness of maternal bone during lactation. Taken together, findings from this study provide important insights into the relationship between reproduction- and lactation-induced skeletal changes and external mechanical loading, emphasizing the importance of weight-bearing exercise on maternal bone health during reproduction and postpartum.

Recovery of the maternal skeleton after lactation is impaired by advanced maternal age but not by reduced IGF availability in the mouse

Background

Lactation results in substantial maternal bone loss that is recovered following weaning. However, the mechanisms underlying this recovery, and in particular the role of insulin-like growth factor 1 (IGF-I), is not clear. Furthermore, there is little data regarding whether recovery is affected by advanced maternal age.

Methods

Using micro-computed tomography, we studied bone recovery following lactation in mice at 2, 5 and 7 months of age. We also investigated the effects of reduced IGF-I availability using mice lacking PAPP-A2, a protease of insulin-like growth factor binding protein 5 (IGFBP-5).

Results

In 2 month old mice, lactation affected femoral trabecular and cortical bone, but only cortical bone showed recovery 3 weeks after weaning. This recovery was not affected by deletion of the Pappa2 gene. The amount of trabecular bone was reduced in 5 and 7 month old mice, and was not further reduced by lactation. However, the recovery of cortical bone was impaired at 5 and 7 months compared with at 2 months.

Conclusions

Recovery of the maternal skeleton after lactation is impaired in moderately-aged mice compared with younger mice. Our results may be relevant to the long-term effects of breastfeeding on the maternal skeleton in humans, particularly given the increasing median maternal age at childbearing.

Bone resorption and dietary calcium in pregnancy-a window to future maternal bone health

BACKGROUND

Pregnancy is characterized by increased bone turnover and reversible loss of bone mineral density (BMD) to meet fetal calcium demands. The long-term effect of bone turnover and maternal diet in pregnancy on maternal bone is not well established.

OBJECTIVE

We aimed to determine if an association exists between [1] bone resorption, [2] dietary calcium, and [3] serum 25-hydroxyvitamin D in pregnancy with maternal BMD 5-year postpartum.

DESIGN

This is a prospective, longitudinal study of 107 women recruited to the ROLO low glycemic index dietary intervention trial in pregnancy and followed-up at 13, 28, and 34 weeks' gestation and 5 years' postpartum. At 13 and 28 weeks' gestation, a biomarker of bone resorption, urine cross-linked N-telopeptide of type I collagen (uNTX), was measured. At the 5-year follow-up BMD was measured using dual-energy X-ray absorptiometry. Anthropometry, dietary intakes, and serum 25-hydroxyvitamin D were measured in pregnancy and at 5 years. Multiple linear regression, controlling for confounders, was used for analysis.

RESULTS

Mean BMD at 5 years was 1.208 g/cm². In pregnancy, 24-34% reported dietary calcium intakes <800 mg/day. Vitamin D deficiency (< 30 nmol/L) was observed in 38-41% of women in pregnancy and in 29% of women at the 5-year follow-up. At 13 and 28 weeks' gestation, uNTX levels greater than the median were associated with 0.060 and 0.050 g/cm² lower BMD 5 years later, respectively. Dietary calcium <800 mg/day in trimester 3 was associated with 0.072 g/cm² lower BMD 5 years later. Vitamin D deficiency at 5 years, but not in pregnancy, was associated with lower BMD.

CONCLUSION

Higher bone resorption and low dietary calcium in pregnancy were associated with lower BMD 5 years later. These findings could enable the identification of women at risk of declining of BMD in later life, but further research is needed. Adequate dietary calcium should be advised in the antenatal setting to promote lifelong maternal bone health.

Pregnancy-Related Change in pQCT and Bone Biochemistry in a Population With a Habitually Low Calcium Intake

In pregnancy, changes in maternal calcium (Ca) economy occur to satisfy fetal Ca demand. It is unclear whether maternal mineral reserves facilitate these requirements and no data exist from sub-Saharan Africa. The aim was to determine skeletal changes with peripheral quantitative computed tomography (pQCT) and bone biochemistry between early second and third trimesters. Pregnant rural Gambians aged 18 to 45 years (n = 467) participating in a trial of antenatal nutritional supplements (ISRCTN49285450) had pQCT scans and blood collections at mean (SD) 14 (3) and 31 (1) weeks' gestation. Outcomes were pQCT: radius/tibia 4% total volumetric bone mineral density (vBMD), trabecular vBMD, total cross-sectional area (CSA), 33%/38% radius/tibia cortical vBMD, bone mineral content (BMC), total CSA; biochemistry: collagen type 1 cross-linked β-C-telopeptide (β-CTX), type 1 procollagen N-terminal (P1NP), parathyroid hormone (PTH), and 1,25(OH)₂ D. Independent t tests tested whether pooled or within-group changes differed from 0. Multiple regression was performed adjusting for age. Data for change are expressed as mean (confidence interval [CI] 2.5, 97.5%). Radius trabecular vBMD, cortical vBMD, and BMC increased by 1.15 (0.55, 1.75)%, 0.41 (0.24, 0.58)%, and 0.47 (0.25, 0.69)%. Tibia total and trabecular vBMD increased by 0.34 (0.15, 0.54)% and 0.46 (0.17, 0.74)%, while tibia cortical vBMD, BMC, and cortical CSA increased by 0.35 (0.26, 0.44)%, 0.55 (0.41, 0.68)% and 0.20 (0.09, 0.31)%, respectively. CTX, PTH, and 1,25(OH)₂ D increased by 23.0 (15.09, 29.29)%, 13.2 (8.44, 19.34)%, and 21.0 (17.67, 24.29)%, while P1NP decreased by 32.4 (-37.19, -28.17)%. No evidence of mobilization was observed in the peripheral skeleton. Resorption, although higher in late versus early gestation, was lower throughout pregnancy compared with non-pregnant non-lactating (NPNL) in the same community. Formation was lower in late pregnancy than in early, and below NPNL levels. This suggests a shift in the ratio of resorption to formation. Despite some evidence of change in bone metabolism, in this population, with habitually low Ca intakes, the peripheral skeleton was not mobilized as a Ca source for the fetus. © 2021 crown copyright . Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR). The article published with the permission of the Controller of HMSO and the Queen's Printer of Scotland..

Severe Bone Microarchitecture Impairment in Women With Pregnancy and Lactation-Associated Osteoporosis

Context

Pregnancy- and lactation-associated osteoporosis (PLO) is a rare condition characterized by fragility fractures, mostly vertebral, during the third trimester of pregnancy or the early postpartum period.

Objective

The aim of this study was to evaluate bone microarchitecture in women with PLO to better understand the pathophysiology of this disease.

Methods

In this retrospective study, we included women with PLO referred to our bone center between November 2007 and July 2012. We assessed bone mineral density (BMD) by dual-energy x-ray absorptiometry, bone turnover markers, and bone microarchitecture by high-resolution peripheral quantitative computed tomography. Results were compared with a control group of healthy lactating women.

Results

Of the 7 primiparous patients with PLO, 6 suffered vertebral fractures and 1 developed a hip fracture during the seventh month of gestation. Fractures occurred within the eighth month of pregnancy and the fourth month post partum; vertebral fractures were multiple in 85.7%. Major or minor risk factors for osteoporosis were present in 86% of our patients. Trabecular density, number, and thickness were 34%, 20% and 22% lower than controls (P < .01, P = .01, and P = .01, respectively). Cortical parameters were also deteriorated but to a lesser extent.

Conclusion

In comparison with healthy lactating women, patients with PLO presented severe deterioration of bone trabecular and cortical microarchitecture. This significant compromise may explain the occurrence of multiple fractures in these otherwise healthy young women. Further prospective studies are needed to determine whether bone microarchitecture might be able to be restored in the future.

Hormonal regulation of biomineralization

Biomineralization is the process by which organisms produce mineralized tissues. This crucial process makes possible the rigidity and flexibility that the skeleton needs for ambulation and protection of vital organs, and the hardness that teeth require to tear and grind food. The skeleton also serves as a source of mineral in times of short supply, and the intestines absorb and the kidneys reclaim or excrete minerals as needed. This Review focuses on physiological and pathological aspects of the hormonal regulation of biomineralization. We discuss the roles of calcium and inorganic phosphate, dietary intake of minerals and the delicate balance between activators and inhibitors of mineralization. We also highlight the importance of tight regulation of serum concentrations of calcium and phosphate, and the major regulators of biomineralization: parathyroid hormone (PTH), the vitamin D system, vitamin K, fibroblast growth factor 23 (FGF23) and phosphatase enzymes. Finally, we summarize how developmental stresses in the fetus and neonate, and in the mother during pregnancy and lactation, invoke alternative hormonal regulatory pathways to control mineral delivery, skeletal metabolism and biomineralization.

Pregnancy and lactation, a challenge for the skeleton

In this review we discuss skeletal adaptations to the demanding situation of pregnancy and lactation. Calcium demands are increased during pregnancy and lactation, and this is effectuated by a complex series of hormonal changes. The changes in bone structure at the tissue and whole bone level observed during pregnancy and lactation appear to largely recover over time. The magnitude of the changes observed during lactation may relate to the volume and duration of breastfeeding and return to regular menses. Studies examining long-term consequences of pregnancy and lactation suggest that there are small, site-specific benefits to bone density and that bone geometry may also be affected. Pregnancy- and lactation-induced osteoporosis (PLO) is a rare disease for which the pathophysiological mechanism is as yet incompletely known; here, we discuss and speculate on the possible roles of genetics, oxytocin, sympathetic tone and bone marrow fat. Finally, we discuss fracture healing during pregnancy and lactation and the effects of estrogen on this process.