Maternal Calcium Research Articles

Intrapartum Magnesium Sulfate Exposure Attenuates Neutrophil Function in Preterm Neonates

Background: Prenatal exposure to magnesium sulfate, a drug that is frequently used for attempted tocolysis in preterm labor, could alter neutrophil functional activity in infants born preterm. Objectives: To determine the association between maternal tocolysis with magnesium sulfate and the cord blood neutrophil functional activity of preterm neonates. Methods: The chemotaxis, random motility, and chemiluminescence of neutrophils were compared in the cord blood of 10 preterm neonates born to mothers tocolysed with magnesium sulfate, 10 preterm infants whose mothers had not received any tocolysis, and 10 term infants. Data regarding the maternal and neonatal magnesium and calcium levels were collected and analyzed in association with the cord blood neutrophil functional activity of the preterm infants. Results: Neutrophil functional activity in the cord blood of the preterm neonates was significantly lower than in term neonates. However, the alteration of neutrophil chemotaxis, random motility and chemiluminescence was more noticeable in neonates with intrapartum exposure to magnesium sulfate as compared to preterm infants whose mothers received no tocolysis (30.9 ± 2.3 vs. 36.7 ± 2.7 µm, p < 0.01; 26.6 ± 1.9 vs. 33.1 ± 3.1 µm, p < 0.01; and 74.3 ± 6.5 vs. 89.9 ± 6.25 ×10³ counts per min (cpm), p < 0.01, respectively). Furthermore, the reduction in neutrophil functional activity of preterm infants with intrapartum exposure to magnesium was directly correlated with the maternal serum magnesium levels (r = –0.90 to –0.85, p < 0.01). Conclusion: In infants born preterm, intrapartum exposure to magnesium sulfate is a risk factor contributing to the alteration in neutrophil motility and post-phagocytic bactericidal capacity.

Relationship between pregnancy outcomes and maternal vitamin D and calcium intake: A cross-sectional study

Poor maternal vitamin D status affects fetal and infant skeletal growth. The aim of the present study was to determine the association between newborn outcomes and maternal calcium and vitamin D intakes. Four hundred and forty-nine pregnant women, healthy at the point of delivery, and their newborns were enrolled in the study, which was performed in three university hospitals in Tehran in March 2004. Maternal anthropometric data and energy, protein, calcium and vitamin D intakes were collected, and newborn outcomes (weight, length, head circumference and 1-min Apgar score) were determined. Almost two-thirds of the mothers (64.3%) took no supplements during pregnancy. Only one-third of the mothers (33.8%) had adequate intakes of calcium and vitamin D (from supplements and foods) compared with the Recommended Dietary Allowances. Mean length at birth and 1-min Apgar score were higher in newborns whose mothers had adequate calcium and vitamin D intake than in newborns whose mothers had inadequate intake (p = 0.03 and p = 0.04, respectively). Significant correlations were found between adequate maternal calcium and vitamin D intake and both appropriate birth weight and 1-min Apgar score of newborns and weight gain of mothers during pregnancy. Informing mothers of the critical importance of consuming adequate amounts of calcium and vitamin D seems necessary.

Maternal calcium and bone metabolism during lactation

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Influence of Maternal Bone Lead Burden and Calcium Intake on Levels of Lead in Breast Milk over the Course of Lactation

The authors studied 367 women who were breastfeeding their infants in Mexico City, Mexico, between 1994 and 1995 to evaluate the effect of cumulative lead exposure, breastfeeding practices, and calcium intake on breast milk lead levels over the course of lactation. Maternal blood and breast milk lead levels were measured at 1, 4, and 7 months postpartum. Bone lead measurements were obtained at 1 month postpartum. At 1, 4, and 7 months postpartum, respectively, the mean breast milk lead levels were 1.4 (standard deviation (SD), 1.1), 1.2 (SD, 1.0), and 0.9 (SD, 0.8) microg/liter and showed a significant decreasing trend over the course of lactation (p < 0.00001). The relations of bone lead and blood lead to breast milk lead were modified by breastfeeding practice, with the highest breast milk lead levels among women with a high level of patella lead who were exclusively breastfeeding. Dietary calcium supplementation increased the rate of decline in breast milk lead by 5-10%, in comparison with a placebo, over the course of lactation, suggesting that calcium supplementation may constitute an important intervention strategy, albeit with a modest effect, for reducing lead in breast milk and thus the potential for exposure by infants.

151 The Usefulness of Quantitative Ultrasound (QUS) Measurements in the Evaluation of Skeletal Status in Newborns and in Children

This study aimed to evaluate both the feasibility and usefulness of QUS in newborns and children and the factors influencing QUS parameters. In 50 consecutive healthy full-term newborns (23 males and 27 females; gestational age: 39,2±2,0 weeks) QUS parameters were assessed within three days of birth at distal diaphysis of humerus using Bone Profiler (IGEA, Italy), after an appropriate modification of calliper and software, and after 4 years of life by the standard technique used in the children and adults. In all subjects we evaluated: AD-SoS (m/s), the characterizing graphic trace parameters (SDy, FWA and BTT), SoS (m/s), that is the speed of sound calculated on the first peak and hBTT, that is the interval time between the first peak of the ultrasound and when this reaches the speed of 1570 m/s, that is the velocity of ultrasound in the soft tissue. This latter parameter allows to measure bone tissue independently of soft tissue. QUS were also performed at phalanges on all mothers, who also self-reported a questionnaire on their obstetric history, smoking and dietary habits and family history of osteoporosis. At birth all QUS parameters were slightly higher in male than in female newborns but the difference was not significant. BTT and hBTT of newborns showed a significant relationship with weight at birth and with the cranial circumference. In newborns none of the QUS parameters was significantly influenced by maternal QUS or by maternal smoking and calcium intake. By using a model of multiple regression analysis the cranial circumference was the only parameter entered into the model, explaining about 15% of hBTT value. At the fourth year of life BTT and ADSoS showed a significant increase with respect to basal values. BTT was positively correlated with the weight (r=0.53; p<0.01). BTT values at birth, expressed as percentile, showed a significant concordance with BTT in percentile at the fourth year of life. In addition, a multiple regression analysis showed that both BTT at birth and weight at the fourth year of life were predictive of BTT after 4 years of life (R2: 0.11; p<0.05 and 0.30, p<0.01 respectively). The present study demonstrates that the assessment of BTT at birth seems to be partially predictive of skeletal status after 4 years of life. In addition, BTT appears to be the best parameter for both evaluation of skeletal status at birth and monitoring of bone growth in the first years of life.

Maternal and Seasonal Predictors of Change in Calcaneal Quantitative Ultrasound during Pregnancy

During pregnancy, mineralization of the fetal skeleton and obligate urinary losses require adaptation of maternal calcium homeostasis, such as increased intestinal calcium absorption and bone resorption. However, the environmental determinants of maternal bone resorption during pregnancy in healthy adult mothers have not been previously described. We conducted a population-based longitudinal study of 307 term pregnancies using a cohort of 307 pregnant women living in Southampton, United Kingdom. During early and late pregnancy, skeletal status was measured at the left calcaneus using quantitative ultrasound (QUS). There was a significant (P < 0.001) decline in both speed of sound and broadband ultrasound attenuation during pregnancy. Those women who were pregnant for the first time (P = 0.001), had low milk intake prepregnancy (P = 0.01), and reduced measures of fat mass (P = 0.01) showed the greatest decline in calcaneal bone measurements. Furthermore, those women who were pregnant over winter months had greater losses in calcaneal QUS (P = 0.02). Maternal lifestyle, fat stores, and seasonality of early pregnancy influence maternal calcaneal QUS loss during pregnancy; the findings support a role for vitamin D supplementation of women pregnant during winter, especially those with low calcium intakes who are pregnant for the first time.

Calcium Sensing by the Mammary Gland

Calcium is an important nutrient that is secreted into milk in quantities that put a considerable stress upon maternal calcium homeostasis. Here we summarize the evidence that two important entities, the extracellular calcium-sensing receptor (CaR) and parathyroid hormone-related protein (PTHrP) are involved in a feedback loop that regulates calcium fluxes to the mammary gland. The CaR may also play a role in regulating milk secretion, and may regulate the proliferation of normal and neoplastic mammary epithelial cells. Finally, the relationship between the CaR and PTHrP in breast cancer cells may promote the formation of osteolytic bone metastases.

The vitamin D receptor is not required for fetal mineral homeostasis or for the regulation of placental calcium transfer in mice

We utilized a vitamin D receptor (VDR) gene knockout model to study the effects of maternal and fetal absence of VDR on maternal fertility, fetal-placental calcium transfer, and fetal mineral homoeostasis. Vdr null mice were profoundly hypocalcemic, conceived infrequently, and had significantly fewer viable fetuses in utero that were also of lower body weight. Supplementation of a calcium-enriched diet increased the rate of conception in Vdr nulls but did not normalize the number or weight of viable fetuses. Among offspring of heterozygous (Vdr(+/-)) mothers (wild type, Vdr(+/-), and Vdr null fetuses), there was no alteration in serum Ca, P, or Mg, parathyroid hormone, placental (45)Ca transfer, Ca and Mg content of the fetal skeleton, and morphology and gene expression in the fetal growth plates. Vdr null fetuses did have threefold increased 1,25-dihydroxyvitamin D levels accompanied by increased 1alpha-hydroxylase mRNA in kidney but not placenta; a small increase was also noted in placental expression of parathyroid hormone-related protein (PTHrP). Among offspring of Vdr null mothers, Vdr(+/-) and Vdr null fetuses had normal ionized calcium levels and a skeletal ash weight that was appropriate to the lower body weight. Thus our findings indicate that VDR is not required by fetal mice to regulate placental calcium transfer, circulating mineral levels, and skeletal mineralization. Absence of maternal VDR has global effects on fetal growth that were partly dependent on maternal calcium intake, but absence of maternal VDR did not specifically affect fetal mineral homeostasis.

Uteroplacental restriction in the rat impairs fetal growth in association with alterations in placental growth factors including PTHrP

During pregnancy, parathyroid hormone-related protein (PTHrP) is one of many growth factors that play important roles to promote fetal growth and development, including stimulation of placental calcium transport. Angiotensin II, acting through the AT(1a) receptor, is also known to promote placental growth. We examined the effects of bilateral uterine artery and vein ligation (restriction), which mimics placental insufficiency in humans, on growth, intrauterine PTHrP, placental AT(1a), and pup calcium. Growth restriction was surgically induced on day 18 of pregnancy in Wistar-Kyoto female rats by uterine vessel ligation. Uteroplacental insufficiency reduced fetal body weight by 15% and litter size (P < 0.001) compared with the control rats with no effect on placental weight or amniotic fluid volume. Uteroplacental insufficiency reduced placental PTHrP content by 46%, with increases in PTHrP (by 2.6-fold), parathyroid hormone (PTH)/PTHrP receptor (by 11.6-fold), and AT(1a) (by 1.7-fold) relative mRNA in placenta following restriction compared with results in control (P < 0.05). There were no alterations in uterine PTHrP and PTH/PTHrP receptor mRNA expression. Maternal and fetal plasma PTHrP and calcium concentrations were unchanged. Although fetal total body calcium was not altered, placental restriction altered perinatal calcium homeostasis, as evidenced by lower pup total body calcium after birth (P < 0.05). The increased uterine and amniotic fluid PTHrP (P < 0.05) may be an attempt to compensate for the induced impaired placental function. The present study demonstrates that uteroplacental insufficiency alters intrauterine PTHrP, placental AT(1a) expression, and perinatal calcium in association with a reduction in fetal growth. Uteroplacental insufficiency may provide an important model for exploring the early origins of adult diseases.

Maternal Calcium Intake and Metabolism During Pregnancy and Lactation

Calcium is an essential nutrient during pregnancy and lactation. Calcium contributes to bone development in the fetus and neonate and is considered a critical nutrient. Physiological changes in calcium metabolism occur during pregnancy and lactation. Some women may lose some of their bone density during pregnancy and/or lactation, and then regain it after the cessation of lactation. Implications for childbirth educators include content regarding the topic of calcium in their classes.

Maternal osteoporosis after prolonged magnesium sulfate tocolysis therapy: A case report

Hung J-W, Tsai M-Y, Yang B-Y, Chen J-F. Maternal osteoporosis after prolonged magnesium sulfate tocolysis therapy: a case report. Tocolysis therapy with magnesium sulfate is known to affect calcium homeostasis. Prolonged infusion of magnesium sulfate (MgSO 4) has been used for the treatment of refractory preterm labor, and has been reported to change maternal calcium homeostasis and possible mineralization. In this case report, we present a woman in her mid thirties who had undergone intravenous MgSO 4 tocolysis therapy, and developed osteoporosis leading to significant morbidity after delivery. The laboratory investigation, including the bone scan, magnetic resonance image, indices of bone turnover, and the results of 2 years of follow-up of bone mineral density, are also reported. This case report supports the existence of a possible association between prolonged intravenous magnesium tocolysis and maternal osteoporosis. To prevent osteoporosis, it is important to avoid a prolonged period of MgSO 4 tocolysis. In cases of prolonged MgSO 4 treatment and bedrest, physicians should be aware of the risk of osteoporosis. The recommended management is also discussed in this report.

Commentary: Maternal calcium intake and offspring cardiovascular risk factors

Commentary: Maternal calcium intake and offspring cardiovascular risk factors

Maternal calcium supplementation and cardiovascular risk factors in twin offspring

There is evidence that maternal calcium supplementation may result in lower offspring blood pressure. We hypothesized that maternal calcium supplementation also influences other cardiovascular risk factors. In the Tasmanian Infant Health Study, supplements reportedly taken in pregnancy were recorded. Twin children of 147 participating mothers were seen at mean age 9 years. Blood pressure was measured in all 294 children and fasting blood samples taken from 230 (78%) for glucose and insulin, triacylglycerol, total cholesterol (T-C) and HDL cholesterol (HDL-C). LDL cholesterol (LDL-C) was calculated. Children of supplemented mothers (n = 110, 77 had venipuncture) had lower geometric mean triacylglycerol, T-C, and LDL-C than other children. After adjustment for potential confounding factors, geometric mean ratios were 0.86 (95% CI: 0.75, 0.98), 0.94, (95% CI: 0.90, 0.99) and 0.90, (95% CI: 0.83, 0.98) respectively. The association with T-C and LDL-C was seen principally among children with BMI > 17.5: estimated ratios 0.85 (95% CI: 0.79, 0.92) for total cholesterol and 0.79 (95% CI: 0.70, 0.90) for LDL cholesterol (P for interaction 0.001 and 0.009 respectively). There was no significant association between maternal calcium supplementation and child size at birth and follow up, blood pressure, fasting glucose or insulin or HDL-C. Maternal calcium supplementation may confer health benefits on twin offspring, especially if they are relatively fat. Calcium availability could permanently programme lipid metabolism during fetal life, directly or by influencing maternal lipid profile. Our findings need to be replicated in other studies and in singletons. If confirmed, our findings could have important implications for population health.

Maternal calcium intake and offspring blood pressure.

Few data exist on the intergenerational influence of calcium intake during pregnancy on offspring blood pressure. As part of the ongoing US prospective cohort study Project Viva, we analyzed 4091 Dinamap blood pressure measurements from 936 six-month-old infants whose mothers had completed food frequency questionnaires during the second trimester of pregnancy. We used mixed models to estimate effects of maternal calcium intake on offspring systolic blood pressure. Mean+/-SD daily total maternal calcium intake was 1494+/-523 mg, consisting of 1230+/-486 mg from foods and 264+/-191 mg from supplements. Mean+/-SD 6-month blood pressure was 89.9+/-12.9 mm Hg. From bottom to top quartile of dietary calcium from foods adjusted for energy intake and measurement conditions, mean infant systolic blood pressures were 91.0, 90.2, 90.9, and 90.2 mm Hg (trend P=0.62). From calcium supplements only, the values were 91.5, 90.2, 90.4, and 88.4 mm Hg (trend P=0.006). After further adjustment for demographic, anthropometric, dietary, social, and economic variables, the decrease in 6-month systolic blood pressure was -3.0 mm Hg (95% CI, -4.9 to -1.1) for each 500-mg increment of maternal supplemental calcium intake during pregnancy. We did not find evidence of effect modification by maternal vitamin D or potassium intake or by infant body mass index. First-trimester calcium intake was not associated with offspring blood pressure. These observational data suggest that supplementing maternal midgestational calcium intake may lower offspring blood pressure, thus helping to prevent hypertension in the next generation.

Feasibility of quantitative ultrasound measurements on the humerus of newborn infants for the assessment of the skeletal status.

Quantitative ultrasound (QUS), although widely used in adults has, so far, been scarcely employed in newborn infants and children. This study aimed to evaluate the feasibility of the use of QUS in newborn children and the factors influencing QUS parameters. In 140 consecutive healthy full-term newborn babies (76 male and 64 female; gestational age: 39.5 +/- 1.5 weeks) QUS parameters were assessed within 3 days of the child's birth at the distal diaphysis of the humerus by use of Bone Profiler, after an appropriate modification of caliper and software. In all subjects we evaluated the amplitude-dependent speed of sound (AD-SoS) (meters per second), the characterizing graphic trace parameters [signal dynamic (SDy), fast wave amplitude (FWA) and bone transmission time (BTT)], SoS (meters per second), that is, the speed of sound calculated on the first peak, and hBTT, that is, the interval time between the first peak of the ultrasound and when this reaches the speed of 1,570 m/s, which is the velocity of ultrasound in the soft tissue. This latter parameter allows one to measure bone tissue independently of soft tissue. QUS measurements were also performed at the phalanges on all mothers (age range 24-38 years), who also completed a self-report questionnaire on their obstetric history, smoking and dietary habits and family history of osteoporosis. In 73 mothers and their children QUS was repeated after 12 months. All QUS parameters were slightly higher in male than in female newborn infants but the difference was not significant. BTT and hBTT of neonates showed a significant relationship with birth weight (r = 0.20; P < 0.05 and r = 0.37; P < 0.01, respectively) and with cranial circumference (r = 0.22; P < 0.05 and r = 0.36; P < 0.01, respectively). In newborn infants none of the QUS parameters was significantly influenced by maternal QUS or by maternal smoking and calcium intake. In a model of multiple regression analysis the cranial circumference was the only parameter entered into the model, explaining approximately 15% of hBTT value. At month 12 AD-SoS and SoS were slightly lower than at birth (-11% and -0.1%, respectively), whereas both BTT and hBTT showed a significant (P < 0001) increase. The present study demonstrated the feasibility of the use of QUS, as assessed by a new measurement approach at the humerus, in the evaluation of skeletal status in neonates. BTT and, above all, hBTT, appears to be the best parameter for both evaluation of skeletal status at birth and monitoring of bone growth in the first year of life.

Nutrition Influences Bone Development from Infancy through Toddler Years

During the last decade a greater appreciation has developed for determining factors that influence bone accretion in healthy children. Nutritional factors that may contribute to bone accretion in infants and toddlers include maternal nutritional status during pregnancy, type of infant feeding, calcium and phosphorus content of infant formula, introduction of weaning foods, and diet during the toddler and preschool years. Maternal vitamin D deficiency during pregnancy is associated with disturbances in neonatal calcium homeostasis, and maternal calcium deficiency leads to reduced neonatal bone mineral content (BMC). Preterm infants are at increased risk of osteopenia, and, although the use of high mineral formula has reduced the risk of osteopenia in these infants, it has not eliminated it. The reason for the long-term bone deficiency among preterm infants is not clear, although lower physical activity levels have been suggested as a potential cause. Studies find that human milk-fed infants have lower bone accretion than do formula-fed infants; that the greater the mineral content of formula, the greater the bone accretion; and that the inclusion of palm olein oil in infant formula may reduce bone mineral accretion. Bone accretion is not influenced by the timing of the introduction of weaning foods, despite higher serum parathyroid hormone (PTH) concentrations among infants who receive solids earlier. There is evidence of calcium intake-by-gene and calcium intake-by-physical activity interactions among toddlers and young children. The long-term effects of these early nutritional influences on later bone health are unknown.

PTH/PTHrP activity and the programming of skeletal development in utero.

There is increasing evidence that nutritional deficiency in utero adversely affects bone development and the risk of developing osteoporosis in later life. Although the mechanisms involved are unknown, circumstantial evidence points to an important role of PTH/PTHrP activity. It is recognized that PTH and PTHrP are critically involved in regulating fetal calcium homeostasis, actions that are mediated at least in part by PPR. As well as playing a central role in the maintenance of calcium homeostasis in the fetus, studies in transgenic mice show that PTH, PTHrP, and PPR exert similar effects on skeletal development in utero, acting to increase the size of the trabecular envelope and decrease that of the cortical envelopes. Taken together, these observations raise the possibility that stimulation of PTH/PTHrP activity in the fetus in response to calcium deficiency acts to increase the size of the trabecular envelope but to reduce that of the cortical envelope. Although any increase in trabecular bone at birth is likely to be relatively transient, a decrease in size of the cortical envelope may have a persistent effect on the trajectory of bone growth in subsequent childhood. Consistent with this proposal, preliminary findings from birth cohort studies suggest that maternal calcium intake and cord blood calcium levels are positively related to bone mass of the offspring as assessed later in childhood. Further studies are justified to determine whether alterations in fetal PTH/ PTHrP activity caused by calcium stress lead to a reduction in size of the cortical envelope at birth that persists into childhood and later adult life and to identify modifiable maternal factors that are responsible for these changes.

Bone Mass Changes In Vivo During the Entire Reproductive Cycle in Rats Feeding Different Dietary Calcium and Calcium/Phosphorus Ratio Content

The purpose of this study was to quantify in vivo the impact of different dietary Ca contents on the maternal total skeleton and skeletal sub-areas in adult rats during pregnancy and lactation, using DXA. Twenty-four female Wistar rats (approximately 5 months old) were mated and divided into three groups (n = 8) and fed one of the following diets, varying only in Ca content (LCD: 0.14%, NCD: 0.6% or HCD: 1.2%). Pups were adjusted to 8-9 per dam. Maternal ionic calcium and in vivo bone mineral density (BMD) were measured at the beginning, after delivery and after weaning. Regardless of the diet, ionized calcium decreased from onset to weaning ( P < 0.05). At weaning, bone mass decreased 7.3% in NCD, 15% in LCD and 10.5% in HCD from initial values. Total skeleton, whole and proximal tibia and spine BMDs only decreased at delivery in the LCD group ( P < 0.05) but, irrespective of the diet, at weaning, they were lower compared to delivery and initial values ( P < 0.05). LCD group presented the lowest BMD in the proximal tibia and spine regions ( P < 0.05). At birth, pups did not present differences, however, at weaning, LCD pups reached the lowest body weight ( P < 0.05), NCD presented the highest body Ca content ( P < 0.05) and there were no differences between LCD and HCD. This in vivo study showed that regardless of the dietary calcium content, the maternal skeleton is slightly affected by pregnancy but severely affected by lactation. However, the degree of such response appears to depend not only on dietary Ca content but also on dietary Ca/P molar ratio.

Normal Acquisition and Loss of Bone Mass

The natural patterns of bone mass accumulation and loss with age represent the templates of individual life cycle periods that are distinguished by marked, physiologically and genetically identifiable, changes in bone mass. During the third trimester of pregnancy, maternal calcium absorption increases and the fetus accumulates about two-thirds of the total bone mass of the term infant. In early infancy, human milk calcium is derived primarily from maternal bone stores, which incur substantial bone losses that are quickly replenished during and after weaning. At puberty, a marked increase in bone mass occurs in conjunction with the initial physical and hormonal changes that characterize this stage. Calcium absorption and bone calcium deposition rates peak in females shortly before menarche. At that time, the bone calcium deposition rate is approximately five times that of adulthood. Skeletal bone mass reaches over 90% of its maximum by age 18 (earlier in females) but does not peak until age 25–30. At some point in mid-life, women experience perimenopause, the 3- to 5-year period prior to menopause during which estrogen levels begin to drop and there are marked increases in bone resorption and loss. Throughout adulthood, calcium absorption efficiency from the diet gradually declines.

Changes in serum markers of bone turnover during normal pregnancy.

Maternal calcium homeostasis adapts during pregnancy to provide for the needs of the growing fetal skeleton. Wide selections of bone turnover markers are currently available to assess the changes taking place; here, data are presented on two serum-based markers. The use of serum-based biochemical bone turnover markers during pregnancy was assessed in a cohort of 41 women recruited prior to conception. Serum N-terminal extension peptide of procollagen (P1NP) was used to monitor bone formation and serum beta-crosslaps (S-CTX) used to assess resorption. Blood samples were measured at five time points from a pre-conceptual baseline, through pregnancy, to the final sample, which was taken within 1 week of delivery. An initial decrease from the baseline in both P1NP and S-CTX was observed at 12 weeks; however, it is suggested that this may be due to the haemodilutional effect of pregnancy rather than a true change in bone turnover. Significant increases from the baseline of both analytes were observed by 36 weeks (P1NP, P = 0.013; S-CTX, P = 0.002), when the calcium demands of the fetus are greatest. This study illustrates the use of serum-based bone turnover markers to assess turnover during normal pregnancy, a time when ionizing radiation cannot be used to assess bone turnover.