Serum calcium concentrations in human pregnancy

Minerals and the Menstrual Cycle: Impacts on Ovulation and Endometrial Health

The role of minerals in female fertility, particularly in relation to the menstrual cycle, presents a complex area of study that underscores the interplay between nutrition and reproductive health. This narrative review aims to elucidate the impacts of minerals on key aspects of the reproductive system: hormonal regulation, ovarian function and ovulation, endometrial health, and oxidative stress. Despite the attention given to specific micronutrients in relation to reproductive disorders, there is a noticeable absence of a comprehensive review focusing on the impact of minerals throughout the menstrual cycle on female fertility. This narrative review aims to address this gap by examining the influence of minerals on reproductive health. Each mineral's contribution is explored in detail to provide a clearer picture of its importance in supporting female fertility. This comprehensive analysis not only enhances our knowledge of reproductive health but also offers clinicians valuable insights into potential therapeutic strategies and the recommended intake of minerals to promote female reproductive well-being, considering the menstrual cycle. This review stands as the first to offer such a detailed examination of minerals in the context of the menstrual cycle, aiming to elevate the understanding of their critical role in female fertility and reproductive health.

Are Twin Pregnancies at Higher Risk for Iron and Calcium Deficiency than Singleton Pregnancies?

The aim of this study was to compare the iron and calcium status in singleton and twin pregnancies and to assess whether there is an increased risk for iron and calcium deficiency in twin gestation. The study included 105 singleton and 9 twin pregnancies at or above 35 weeks of gestation. Information on prenatal supplementation with iron or calcium was acquired, and adverse perinatal outcomes were recorded. Biosamples from all 114 mothers and 73 newborns (61 singleton and 12 twin newborns) were finally analyzed. Total iron and calcium concentrations in serum were measured through total reflection X-ray fluorescence analysis. The results indicated no significant differences in maternal serum iron and calcium concentrations between singleton and twin pregnancies. Similarly, iron and calcium concentrations in newborn umbilical cord serum samples were not different between singleton and twin pregnancies. The comparison of total iron and calcium between mothers and umbilical cord serum indicated significantly lower concentrations in the mothers, with the differences being not homogenous but rather pair-specific. A significant positive correlation between maternal serum and umbilical cord serum calcium concentration was noticed. Prenatal iron supplementation was associated with higher iron concentrations in both mothers and newborns, supporting the efficiency of supplementation and the quality of the study methods. Collectively, the data indicate no significant differences in serum iron and calcium concentrations with regard to singleton or twin pregnancies and the efficiency of iron supplementation during pregnancy for increasing iron status.

An update on the physiologic changes during pregnancy and their impact on drug pharmacokinetics and pharmacogenomics

For many years, the medical community has relied in clinical practice on historic data about the physiological changes that occur during pregnancy. However, some newer studies have disputed a number of assumptions in these data for not being evidence-based or derived from large prospective cohort-studies. Accurate knowledge of these physiological changes is important for three reasons: Firstly, it facilitates correct diagnosis of diseases during pregnancy; secondly, it enables us to answer questions about the effects of medication during pregnancy and the ways in which pregnancy alters pharmacokinetic and drug-effects; and thirdly, it allows for proper modeling of physiologically-based pharmacokinetic models, which are increasingly used to predict gestation-specific changes and drug-drug interactions, as well as develop new knowledge on the mode-of-action of drugs, the mechanisms underlying their interactions, and any adverse effects following drug exposure. This paper reviews new evidence regarding the physiologic changes during pregnancy in relation to existing knowledge.

Evidence-Based Recommendations for an Optimal Prenatal Supplement for Women in the U.S., Part Two: Minerals

The levels of many essential minerals decrease during pregnancy if un-supplemented, including calcium, iron, magnesium, selenium, zinc, and possibly chromium and iodine. Sub-optimal intake of minerals from preconception through pregnancy increases the risk of many pregnancy complications and infant health problems. In the U.S., dietary intake of minerals is often below the Recommended Dietary Allowance (RDA), especially for iodine and magnesium, and 28% of women develop iron deficiency anemia during their third trimester. The goal of this paper is to propose evidence-based recommendations for the optimal level of prenatal supplementation for each mineral for most women in the United States. Overall, the evidence suggests that optimal mineral supplementation can significantly reduce a wide range of pregnancy complications (including anemia, gestational hypertension, gestational diabetes, hyperthyroidism, miscarriage, and pre-eclampsia) and infant health problems (including anemia, asthma/wheeze, autism, cerebral palsy, hypothyroidism, intellectual disability, low birth weight, neural tube defects, preterm birth, rickets, and wheeze). An evaluation of 180 commercial prenatal supplements found that they varied widely in mineral content, often contained only a subset of essential minerals, and the levels were often below our recommendations. Therefore, there is a need to establish recommendations on the optimal level of mineral supplementation during pregnancy.

Serum calcium level among pregnant women and its association with pre-eclampsia and delivery outcomes: A cross-sectional study from North India

Background:

Calcium requirement increases during pregnancy, thereby increasing the chances of developing hypocalcaemia. Hypocalcaemia may be associated with pregnancy-related complications. Therefore, we planned this study to estimate the prevalence of hypocalcaemia among pregnant women attending secondary care hospital, and to study the association between hypocalcaemia and pregnancy outcomes.

Materials and Methods:

This study was conducted in a secondary level hospital at Ballabgarh, district Faridabad, Haryana, India. Consecutive pregnant women with gestation period more than 28 weeks were enrolled. Dietary calcium intake was ascertained using 24-hour dietary recall method. Serum calcium estimation was done by Biolis 24i auto analyser. Outcome of pregnancy (preterm delivery, low birth weight (LBW) babies, and neonatal mortality) was assessed telephonically 3 months after the enrolment.

Results:

A total of 696 pregnant women were enrolled in the study. Mean (SD) dietary calcium intake and serum calcium level was 796.4 (360.4) mg/day and 9.56 (0.94) mg/dl respectively. Prevalence (95% CI) of hypocalcaemia was 23.9% (20.8 – 27.2%). Serum total calcium level was not associated with dietary calcium intake (p-value = 0.36). Mean serum calcium level was significantly lower in mothers who had LBW babies. Pre-eclampsia, preterm delivery, and neonatal mortality were not associated with serum calcium level.

Conclusion:

Serum calcium level may not be related to dietary calcium level. Hence, the current recommendation of calcium supplementation during antenatal period appears to be inconclusive among our study population.

Standards of care for hypoparathyroidism in adults: a Canadian and International Consensus

PURPOSE

To provide practice recommendations for the diagnosis and management of hypoparathyroidism in adults.

METHODS

Key questions pertaining to the diagnosis and management of hypoparathyroidism were addressed following a literature review. We searched PubMed, MEDLINE, EMBASE and Cochrane databases from January 2000 to March 2018 using keywords 'hypoparathyroidism, diagnosis, treatment, calcium, PTH, calcidiol, calcitriol, hydrochlorothiazide and pregnancy'. Only English language papers involving humans were included. We excluded letters, reviews and editorials. The quality of evidence was evaluated based on the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach. These standards of care for hypoparathyroidism have been endorsed by the Canadian Society of Endocrinology and Metabolism.

RESULTS

Hypoparathyroidism is a rare disease characterized by hypocalcemia, hyperphosphatemia and a low or inappropriately normal serum parathyroid hormone level (PTH). The majority of cases are post-surgical (75%) with nonsurgical causes accounting for the remaining 25% of cases. A careful review is required to determine the etiology of the hypoparathyroidism in individuals with nonsurgical disease. Hypoparathyroidism is associated with significant morbidity and poor quality of life. Treatment requires close monitoring as well as patient education. Conventional therapy with calcium supplements and active vitamin D analogs is effective in improving serum calcium as well as in controlling the symptoms of hypocalcemia. PTH replacement is of value in lowering the doses of calcium and active vitamin D analogs required and may be of value in lowering long-term complications of hypoparathyroidism. This manuscript addresses acute and chronic management of hypoparathyroidism in adults.

MAIN CONCLUSIONS

Hypoparathyroidism requires careful evaluation and pharmacologic intervention in order to improve serum calcium and control the symptoms of hypocalcemia. Frequent laboratory monitoring of the biochemical profile and patient education is essential to achieving optimal control of serum calcium.

Serum Calcium and Magnesium Levels in Normal Ghanaian Pregnant Women: A Comparative Cross-Sectional Study

BACKGROUND:

Pregnancy is described as a normal physiologic state associated with various biochemical changes. Magnesium and calcium are essential macronutrients required for foetal growth. Complications associated with their deficiency during normal pregnancy include; low neonatal birth weight, pre-eclampsia, eclampsia and preterm labour. Changes in serum levels of magnesium and calcium in normal pregnancy have not been extensively studied among Ghanaian women.

AIM:

To determine the variation in serum magnesium and calcium levels with gestational age in normal pregnancy in Ghanaian women.

METHODS:

A hospital-based comparative cross-sectional study was conducted among 32 normal non-pregnant women (Group A) and 100 normal pregnant women (Group B) attending the clinic at the Korle-Bu Teaching hospital. The group B pregnant women were further divided into Group B1 (n = 33), Group B2 (n = 37) and Group B3 (n = 30) based on their pregnancy gestation as first, second and third trimester respectively. Blood samples were obtained from the antecubital vein of subjects and total serum calcium, magnesium, protein and albumin were estimated. Data obtained were analysed using SPSS for windows version 20. Analysis of variance (ANOVA) was employed to determine the statistical differences between the groups. A p-value of ≤ 0.05 was considered significant.

RESULTS:

Mean serum total calcium and magnesium in first, second and third trimester normal pregnant women were 2.14 ± 0.16, 2.13 ± 0.44, 2.13 ± 0.35 mmol/L and 0.77 ± 0.11, 0.77 ± 0.16 and 0.76 ± 0.14 mmol/L respectively. Mean serum total calcium and magnesium levels in non-pregnant women were 2.20 ± 0.16 and 0.80 ± 0.10 mmol/L respectively. There was a statistically non-significant difference in serum total calcium and magnesium between non-pregnant and normal pregnant women, with p-values of 0.779 and 0.566 respectively. Mean total serum protein and albumin in first, second and third-trimester normal pregnant women were 68.42 ± 10.37, 70.46 ± 6.84, 66.70 ± 7.83 g/L and 39.92 ± 3.22, 40.75 ± 8.06, 38.26 ± 3.02 g/L respectively. Mean total serum protein and albumin in non-pregnant women were 73.13 ± 7.02 and 42.94 ± 3.03 g/L respectively. Mean total serum protein and albumin levels were lower in pregnant women as compared to non-pregnant women with the difference being significant in the third trimester (p-values of 0.012 and 0.002).

CONCLUSION:

Total serum calcium and magnesium levels in normal pregnancy were non-significantly lower compared to non-pregnant women in Ghana. There was a reduction in total serum protein, and albumin levels during pregnancy with a significant reduction noticed during the third trimester compared to the non-pregnant state.

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.

Dynamic changes in serum 25-hydroxyvitamin D during pregnancy and lack of effect on thyroid parameters

Background & Aims

To explore vitamin D status and its dynamic changes during pregnancy in women living in Northeast China. The association between 25-hydroxyvitamin D and serum calcium, phosphate and parathyroid hormone was studied. Because vitamin D deficiency or thyroid dysfunction/autoimmunity during pregnancy may lead to similar adverse events, the relationship between 25-hydroxyvitamin D and thyroid parameters was investigated.

Methods

Serum samples of 50 women (aged 22 to 36 years) were selected retrospectively. The samples were collected at gestational 8 weeks ±3 days, 20 weeks ±3 days and 32 weeks ±3 days for measurement of 25-hydroxyvitamin D, calcium, phosphate, parathyroid hormone, and thyroid parameters.

Results

The median 25-hydroxyvitamin D levels were 28.29, 39.23 and 40.03 nmol/L, respectively, from the first to the third trimester. The 25-hydroxyvitamin D concentration during the first trimester was significantly lower than the next two trimesters (p<0.01) and was unchanged between the second and the third trimester. Of these women, 96%, 78% and 76% showed 25-hydroxyvitamin D ≤50 nmol/L during each trimester. Season was associated with 25-hydroxyvitamin D during each trimester (p<0.05), and a significant association was found between calcium and 25-hydroxyvitamin D during the first and the second trimesters. Only triiodothyronine was associated with 25-hydroxyvitamin D in the first trimester (p = 0.024), but statistical significance was only a trend (p = 0.063) after excluding abnormal values. No association was observed between 25-hydroxyvitamin D and phosphate, parathyroid hormone, and other thyroid parameters.

Conclusions

Vitamin D deficiency during pregnancy was prevalent in women from Northeast China who did not use supplementation. No significant relationships were observed between 25-hydroxyvitamin D and thyroid parameters during pregnancy.

Primary hyperparathyroidism in pregnancy-a rare cause of life-threatening hypercalcemia: case report and literature review

Objective. To report a case of primary hyperparathyroidism in a pregnant patient, report the obstetric and neonatal outcomes, and review the relevant literature. Results. A 29-year-old primigravida was successfully treated for PHP with minimally invasive resection of a parathyroid adenoma in the second trimester of pregnancy. A healthy baby girl was delivered at 37-week gestation with an unremarkable neonatal course. To the best of our knowledge, this is the second case report in the literature utilizing intraoperative PTH during a parathyroidectomy in a pregnant woman. Conclusions. Primary hyperparathyroidism is a rare life-threatening condition that can present during pregnancy. The diagnosis can be difficult to establish during pregnancy, given the nonspecific symptoms related to hypercalcemia. However, a better understanding of the condition, improved diagnostic studies, and well-organized multidisciplinary management decisions can significantly reduce the morbidity and mortality associated with the disease during pregnancy. This case report is presented to highlight the value of early diagnosis and appropriate management of PHP during pregnancy.

Blood copper, zinc, calcium, and magnesium levels during different duration of pregnancy in Chinese

Concentrations of various trace elements are altered during pregnancy with changes in the mother's physiology and the requirements of growing fetus. The aim of the present longitudinal study was to learn the changes of trace element copper (Cu), zinc (Zn), calcium (Ca), and magnesium (Mg) of normal pregnant woman during different durations of pregnancy and establish the reference values of changes of statistical significance. Blood samples were obtained from 128 normal pregnant women during early (10-14th week), mid (20-24th week), and late (30-34th week) pregnancy and 6-12th week postpartum and 120 healthy unpregnant healthy women. The full blood concentrations of chosen elements were measured by means of an atomic absorption spectrophotometer. Changes on levels of Cu, Ca, and Mg during all the three durations of pregnancy and Zn during mid and late pregnancy and postpartum were of statistical significance and new reference values of them were set in the present study. These new reference values will be helpful in assessing the health status of pregnant women with a socioeconomic and racial background similar to those of our study participants and give treatments to them promptly.

Profound Vitamin D Deficiency in a Diverse Group of Women during Pregnancy Living in a Sun-Rich Environment at Latitude 32°N

OBJECTIVE

Determine prevalence of vitamin D deficiency (VDD) in a diverse group of women presenting for obstetrical care at two community health centers in South Carolina at latitude 32°N.

METHODS AND DESIGN

Any pregnant woman presenting for care at 2 community health centers was eligible to participate. Sociodemographic and clinical history were recorded. A single blood sample was taken to measure circulating 25(OH)D as indicator of vitamin D status [25(OH)D < 20 ng/mL (50 nmol/L deficiency; <32 ng/mL (80 nmol/L) insufficiency]. Total serum calcium, phosphorus, creatinine, and intact parathyroid hormone also were measured.

RESULTS

559 women, [mean age 25.0 ± 5.4 (range 14-43) years] participated: African American (48%), Hispanic (38%), Caucasian/Other (14%). Mean gestational age was 18.5 ± 8.4 (median 14.6, range 6.4-39.6) weeks' gestation. 48% were VDD; an additional 37% insufficient. Greatest degree was in the African American women (68% deficient; 94% insufficient). In multivariable regression, 25(OH)D retained a significant negative association with PTH (P < .001).

CONCLUSIONS

VDD was high in a diverse group of women, greatest in those of darker pigmentation. The negative correlation between 25(OH)D and PTH confirms their corroborative use as biomarkers of VDD. These findings raise the issue of adequacy of current vitamin D recommendations for pregnant women.

Calcium in midpregnancy

OBJECTIVE

To establish reference value for serum calcium concentration and urinary calcium excretion during mid pregnancy and to find out variation of calcium intake in pregnant women.

MATERIALS AND METHODS

This was a cross sectional study conducted in antenatal clinic of department of Obstetrics and Gynaecology. A total of 543 pregnant women with pregnancy period of second trimester were enrolled for the study. Eligible healthy, vegetarian primigravid women provided serum and 24 h urinary samples for determination of serum calcium and urinary calcium excretion. Dietary intake calculated by 3-day recall method. Variation of calcium intake according to various demographic characteristics was noted.

RESULTS

Statistical analysis done with SPSS software. The mean total serum calcium and 24 h urinary calcium and dietary intake of calcium were 8.1+/-1.5 mg/dl (5.1-11.9), 129.56+/-67.08 mg (40.5-400) and 324.37+/-199.47 mg/day (85.71-910.71) respectively. The 95th percentiles for serum calcium were 10.56 mg/dl and urinary calcium excretion was 280.70 mg/24 h. Educational level, monthly income and height were positive correlated with calcium intake.

CONCLUSION

This preliminary study defines the first standard value for calcium status in pregnant second trimester females of northern India. Calcium intake in pregnant females is affected by various demographic characteristics. There is need to change dietary pattern by improving education and socio-economic level.

Release of lead from bone in pregnancy and lactation

Concentrations and isotope ratios of lead in blood, urine, 24-h duplicate diets, and hand wipes were measured for 12 women from the second trimester of pregnancy until at least 8 months after delivery. Six bottle fed and six breast fed their infants. One bottle feeder fell pregnant for a second time, as did a breast feeder, and each was followed semicontinuously for totals of 44 and 54 months, respectively. Bone resorption rather than dietary absorption controls changes in blood lead, but in pregnancy the resorption of trabecular and cortical bone are decoupled. In early pregnancy, only trabecular bone (presumably of low lead content) is resorbed, causing blood leads to fall more than expected from hemodilution alone. In late pregnancy, the sites of resorption move to cortical bone of higher lead content and blood leads rise. In bottle feeders, the cortical bone contribution ceases immediately after delivery, but any tendency for blood leads to fall may be compensated by the effect of hemoconcentration produced by the postpartum loss of plasma volume. In lactation, the whole skeleton undergoes resorption and the blood leads of nursing mothers continue to rise, reaching a maximum 6-8 months after delivery. Blood leads fall from pregnancy to pregnancy, implying that the greatest risk of lead toxicity lies with first pregnancies.

Calcium in pregnancy and lactation

Pregnancy and lactation are periods of high calcium requirement. This review highlights recent advances in our understanding of calcium and bone metabolism during human pregnancy and lactation and discusses the findings in relation to the calcium nutrition of the mother. The evidence indicates that pregnancy and lactation are characterized by physiological adaptive processes that are independent of maternal calcium intake and that provide the calcium necessary for fetal growth and breast-milk production without requiring an increase in maternal calcium intake. There are firm data that demonstrate that a low calcium intake during lactation does not lead to impaired lactational performance or to exaggerated bone loss. However, more research is required to define whether a low calcium intake prior to or during pregnancy can have deleterious effects on reproductive and lactational performance, and on the long-term health of the mother and child.

Fetal ionized magnesium levels parallel maternal levels during magnesium sulfate therapy for preeclampsia

OBJECTIVE

Little is known about ion regulation in fetuses. Our aim was to determine the effects of magnesium sulfate therapy on ionized (bioactive) magnesium in the cord blood of pregnancies complicated by preeclampsia.

STUDY DESIGN

Seventy-four pregnant women were studied (37 preeclamptic and 37 controls matched for maternal age, gravidity, and gestational age). The preeclamptic women received intravenous magnesium sulfate 6 gm load followed by 2 gm/hour for > or = 4 hours; controls were not preeclamptic and received no magnesium. Maternal venous and fetal cord blood samples were obtained from study and control patients and were analyzed for sodium, potassium, total magnesium, ionized magnesium, total calcium, and ionized calcium. Comparisons between the groups were made and analyzed by the Mann-Whitney U test.

RESULTS

There were no significant differences between the treatment and control group cord samples with respect to sodium or potassium. However, total magnesium and ionized magnesium were significantly elevated (p < 0.001) in cord samples of the treated group. At the same time ionized calcium and total calcium were reduced. Interestingly, ionized calcium levels were lower in preeclamptic women before magnesium sulfate therapy was begun, whereas total calcium levels were not different. Importantly, there was no difference between maternal and fetal ionized magnesium levels in either treatment or control groups.

CONCLUSIONS

In preeclamptic women undergoing magnesium sulfate therapy, ionized magnesium levels in cord blood parallel maternal levels. Before magnesium therapy ionized calcium levels were lower in preeclamptic women than in matched controls. In the presence of elevated magnesium levels ionized calcium appears to be tightly regulated.

Osteoporosis in pregnancy

Osteoporosis has long been described in pregnant women who developed vertebral fractures in the last trimester or shortly after delivery without underlying disorders. However, this condition appears to be relatively rare and the clinical features, associated metabolic abnormalities and a pathological mechanism have not been fully established. This paper reviews available data on osteoporosis and pregnancy and briefly discusses the relationship between pregnancy and bone mass, calcium homeostasis, systemic skeletal hormones and local factors to help explain the pathophysiology of this unique disorder.

Calcium supplementation prevents pregnancy-induced hypertension by increasing the production of vascular nitric oxide

Pregnancy-induced hypertension (PIH) remains a common cause of maternal and fetal morbidity and mortality. During the past 7 years, some progress has been made in the prevention of PIH. Specifically, clinical studies have shown that supplementation with calcium can significantly reduce the frequency of PIH, specially in populations with a low calcium intake. We have suggested that, in such a population, calcium supplementation is a safe and effective measure for reducing the frequency of PIH. Thus, the purpose of this article is to advance a hypothesis about the mechanism by which calcium supplementation reduces the risk of PIH. We propose that dietary calcium supplementation reduces the frequency of PIH by maintaining the serum ionized calcium level which is crucial for the production of endothelial nitric oxide, the increased generation of which maintains the vasodilatation that is characteristic of normal pregnancy.

Calcium metabolism, calcium supplementation and hypertensive disorders of pregnancy

In recent years growing attention has been directed towards the possible role of calcium in the development of pregnancy-induced hypertension and preeclampsia. Several studies describe calcium metabolism in normal and hypertensive pregnancy, but so far, they have shown discrepant and inconsistent results. Intracellular free calcium, which plays an important role in vascular smooth muscle contraction, has been claimed as a pathogenic factor in hypertensive disorders of pregnancy. Although there is discordance in the data, a possible role of intracellular calcium in the development of hypertensive disorders of pregnancy cannot be excluded. Observational studies in pregnant women suggest an inverse association between calcium intake and the incidence of hypertensive disorders of pregnancy. Despite large methodological differences, the results from the calcium supplementation trials support this finding. Although it is rather difficult to isolate the effect of calcium intake from the intake of other mineral elements, results from calcium supplementation trials are supportive for calcium being the most important. Proposed mechanisms by which calcium supplementation may lower blood pressure involve changes in parathyroid hormone (PTH) level, the renin-angiotensin system and calcium as a modifier of vascular agent regulation, but none of these have yet been elucidated. At present, circumstantial evidence suggest a positive role for calcium in the prevention of hypertensive disorders of pregnancy, but definite evidence is lacking and further research is warranted.

Hypocalcemia and pregnancy-induced hypertension produced by maternal fasting

During pregnancy, maternal calcium needs increase as a result of increasing calcium requirements for fetal bone development. These needs have to be completely supplied by the mother via placental transfer. Several studies link low serum ionized calcium concentrations with the development of hypertension and pregnancy-induced hypertension. We hypothesized that maternal hypocalcemia would develop concomitantly with the development of hypertension in sheep that were fasted in late gestation. Sixteen instrumented ewes were used in the present study. After a 2-day baseline period, food was withdrawn from 10 animals in the experimental group (group 2) for 3 days, whereas the remaining six were allowed to eat and drink normally (group 1). Blood pressure, uteroplacental blood flow, and heart rate were monitored daily. Fasted animals were given deionized water (calcium free) to drink, whereas control animals were given tap water containing 32.9 mg/l calcium concentration. Based on the analysis of the ionized calcium concentration response to fasting, group 2 animals were placed in one of two groups: hypocalcemia did not develop in group 2a, whereas in group 2b the ionized calcium concentration decreased 27% (from 1.09 +/- 0.07 to 0.80 +/- 0.06 mM, p = 0.01) by the third day of fasting. Group 2b responded with a 16% elevation in maternal blood pressure (p = 0.01) and a 43% reduction in uteroplacental blood flow. Furthermore, a positive correlation was found between maternal and fetal blood ionized calcium concentrations (r = 0.860).(ABSTRACT TRUNCATED AT 250 WORDS)

The crucial role of physiological Ca2+ concentrations in the production of endothelial nitric oxide and the control of vascular tone

1. The effect of varying the extracellular Ca2+ concentration on the basal and acetylcholine (ACh)-induced release of nitric oxide (NO) from the rabbit aorta was investigated by use of a superfusion bioassay system. 2. Changes between 0.5 and 2.0 mM in the concentration of Ca2+ superfusing the detector bioassay tissues or perfusing endothelium-denuded donor aortae had no effect on the tone of these tissues. 3. Increasing the concentration of Ca2+ perfusing endothelium-containing donor aortae from zero to 1.25 mM caused a transient (24 +/- 9 min), concentration-dependent basal release of NO, which was attenuated at higher concentrations of Ca2+ (1.5-2.0 mM). 4. The duration of the effect of Ca2+ on the basal release of NO was increased by a concomitant infusion of L-arginine (100 microM) through the donor aorta. 5. Changes in the concentration of Ca2+ between 0.5 and 2.0 mM had a similar biphasic effect on the release of NO induced by ACh, which was also maximal at 1.25 mM Ca2+. 6. When Ca2+ was removed from the Krebs buffer perfusing the donor aorta, the basal release of NO declined within 2 min. In contrast, the release of NO induced by ACh declined progressively over 60 min. 7. Thus changes in the concentration of Ca2+ around the physiological range modulate the synthesis of NO by the vascular endothelium and consequently, vascular tone. This may account for the effects of dietary Ca2+ supplements on the control of some hypertensive states.

Gestational hypercalciuria causes pathological urine calcium oxalate supersaturations

Although normal pregnant women are more hypercalciuric than women with calcium oxalate nephrolithiasis (243 +/- 23 mg/day vs. 194 +/- 5 mg/day), pregnancy is not an established stone-forming state and pregnant women do not exhibit pathological crystalluria. One hypothesis to explain their lack of overt stone formation and pathological crystalluria is that pregnancy does not raise urine supersaturation with respect to stone forming salts such as calcium oxalate or calcium monohydrogen phosphate (brushite) to levels as high as in stone forming women. To test this hypothesis, we studied eleven normal women during each trimester of pregnancy, and between six and eight weeks post-partum. During pregnancy, hypercalciuria occurs with unchanged urine volume, citrate and magnesium excretions do not increase proportionally with calcium excretion, and urine pH increases. Supersaturations with respect to calcium oxalate (CaOx) and brushite (Br) are as high as those of women with calcium nephrolithiasis. The lack of pathological crystalluria and stones during pregnancy is not due to a failure of supersaturations to increase; urinary potential for crystallization is as high as in patients with established stone disease.

Subclinical pseudohypoparathyroidism type II: evidence for failure of physiologic adjustment in calcium metabolism during pregnancy

Patients with latent disorders of hormone response mechanism are rarely found. This paper reports a case of subclinical pseudohypoparathyroidism type II in which physiological adjustment of calcium (Ca) metabolism became insufficient only in the second half of pregnancy. A 34-year-old woman examined for a slight bruise on the head was incidentally found to have marked intracranial calcification and a full set of false teeth. From her history of past pregnancy, it was revealed that she suffered from symptoms of hypocalcemia during late gestation (serum total Ca level, 4.8-6.4 mg/dl), which disappeared spontaneously after delivery. When the woman was not pregnant, although only the total Ca level was slightly below the normal range (7.7-8.4 mg/dl), the serum ionized Ca, phosphorus (P), magnesium, 1,25-dihydroxycholecalciferol and 24,25-hydroxycholecalciferol levels, plasma parathyroid hormone (PTH) level and urinary excretion of Ca were all normal without treatment. Intravenous infusion of 30 mg/kg EDTA-2Na resulted in marked elevation of plasma PTH associated with significant reduction of serum ionized Ca. In contrast, although her urinary excretion of phosphorous per hour was within the normal range in the basal state, she showed no proportional change in urinary phosphorous excretion with increase in urine cyclic AMP induced by administration of PTH(1-34). From these findings, she was diagnosed as having an incomplete form of pseudohypoparathyroidism Type II. This abnormality seems to be rare, but we consider that the present observations provide important information for preventive care of pregnant women and fetuses during gestation.

Primary hyperparathyroidism: changes on biochemical and hormonal profile related to pregnancy

A woman with mild asymptomatic hypercalcemia due to primary hyperparathyroidism became pregnant and her serum calcium normalized while her hypophosphatemia worsered. The PTH was low normal, but her urinary cAMP was elevated. In the second trimester of pregnancy a parathyroid adenoma was removed. After surgery, a transient hypocalcemia that normalized ten days later, a partial recovery of hypophosphatemia, and a 40% reduction of the elevated urinary cAMP excretion were observed. Pregnancy continued uneventful and a normal newborn was delivered. This case demonstrates the diagnostic difficulties posed by primary hyperparathyroidism during pregnancy, derived from inapparent changes in serum calcium and PTH. However, phosphorus and urinary cAMP deviations are significant constituting the basis for a correct diagnosis.

Parity and vitamin D metabolites

Twenty-five hydroxycalciferol (25-OHD), 1,25-dihydroxyvitamin D (1,25(OH)2D), calcium (Ca), phosphorus (P), alkaline phosphatase, and total protein were estimated in 86 Saudi pregnant women. They were divided into two groups, group I, parity 5 or more, and group II, parity 4 or less. The mean level of 25-OHD was 10.4 (S.D. 6.5) ng/ml in group I, and for group II 8.2 (6.1) ng/ml with no significant statistical difference between the groups. 1,25(OH)2D mean levels, in group I 45.5 (S.D. 30.2) ng/ml and in group II 36.9 (S.D. 27.1) pg/ml, also showed no significant difference. Levels of vitamin D metabolites were comparable with non-pregnant levels in Saudi Arabia but lower than others reported in Western populations. We found no effect of increasing parity on levels of vitamin D metabolites in our study.

Determination of trace and bulk elements in plasma and erythrocytes of diabetic pregnant women by PIXE method

Proton-Induced X-Ray Emission (PIXE) analysis of blood samples from diabetic pregnant women was carried out. Elements S, Ca, P, K, Cl, Fe, Zn, Cu, Rb and Br were detected in red blood cells, while S, Ca, P, K, Cl, Fe, Zn, Cu, Ni, Br in the plasma. The concentrations of P, S, Ni, Cu were found to be higher, while those of K, Fe, and Zn were lower in diabetic plasma than in controls. Significantly higher concentrations were measured for P, S, Cl, Fe, Zn and Rb in diabetic erythrocytes compared to normals. Statistical evaluation of the results also indicated significant alteration in the changes of concentrations throughout the pregnancy. Diabetes also resulted in changes in most of the correlations observed in normal pregnancy between the concentrations of elements.

Ionic calcium levels during pregnancy, at delivery and in the first hours of life

Free calcium ion concentration (mmol/l) and pH were determined in whole blood using a semiautomatic electrode system (ICA-1 Radiometer, Copenhagen, Denmark) in 37 normal women, 90 pregnant women (30 from each trimester of gestation), 28 mothers at delivery and their respective newborns. The blood samples from normal controls, pregnant women, umbilical cord and 40-50-hour-old infants were collected anaerobically in vacuum tubes. Duplicate samples drawn from newborns shortly after birth by heel puncture were collected in special heparinized capillary tubes. We observed that Ca2+ concentrations in the second (1.20 +/- 0.04) and third (1.20 +/- 0.05) trimesters of pregnancy, and at delivery (1.18 +/- 0.05), were lower than in the control group (1.23 +/- 0.04). The [Ca2+] in samples from the umbilical vein (1.44 +/- 0.11) and artery (1.45 +/- 0.08) and from newborns 2-5 min after birth (1.34 +/- 0.12) was greater than in control samples. The [Ca2+] in newborns 40-50 hours after birth was lower (1.16 +/- 0.14) than in the control group.

Hypercalcemia in the etiology of puerperal psychosis

The serum calcium of 53 recently delivered mothers hospitalized for severe puerperal psychiatric illness, which represented the whole intake from a defined catchment area, was compared with that of 35 female psychiatric patients and that of 49 normal postnatal women. The mean corrected and ionized serum calcium values of the puerperal psychiatric patients with no personal or family history of psychiatric disorder were markedly above the normal range. They were also significantly higher than those of the puerperal psychiatric patients with a personal or family history of psychiatric illness and those of the two control groups. There was a modest positive correlation between the degree of hypercalcemia and the severity of the psychiatric illness. The follow-up of 16 puerperal psychiatric patients indicated that the fall in ionized serum calcium levels correlated positively and significantly with the improvement in rated symptomatology. Patients with severe puerperal psychiatric disorder can be divided etiologically into two groups. The larger proportion is psychiatrically vulnerable, but in the remainder (about a third of the total number), the psychiatric illness appears to be related to a disorder of calcium homeostasis in the puerperium.

Cytochemical bioassay of parathyroid hormone in maternal and cord blood

Parathyroid hormone and calcium were measured in plasma taken from pregnant women at term and from the umbilical veins of their infants at birth. Three assays were used to measure parathyroid hormone, a cytochemical bioassay of bioactivity and two immunoradiometric assays, one specific for the amino terminus, the other specific for the carboxy terminus of the parathyroid hormone molecule. Plasma calcium was significantly higher in the infants than in the mothers. Maternal parathyroid hormone bioactivity and the amino terminus were both slightly raised, but the carboxy terminus value was normal; these findings supported the view that late pregnancy is a time of mild physiological hyperparathyroidism. In the infants, the amino terminus was undetectable and the carboxy terminus was either undetectable or towards the lower end of the normal range: bioactivity of parathyroid hormone was considerably raised and was related to the gradient of calcium across the placenta. This suggests that the parathyroid glands are not suppressed during fetal life and that they may play an important part in the maintenance of high fetal plasma calcium concentrations.

Calcium metabolism in pregnancy and the perinatal period: a review

Calcium homeostasis is a complex process involving calcium, other involved ions, and three calcitropic hormones, parathyroid hormone, calcitonin, and 1,25-dihydroxyvitamin D3. The principal maternal adjustment during pregnancy is an increasing parathyroid hormone secretion which maintains the serum calcium concentration in the face of a falling albumin level, an expanding extracellular fluid volume, an increasing renal excretion, and placental calcium transfer. The placenta transports calcium ions actively, making the fetus hypercalcemic relative to its mother, which in turn stimulates calcitonin release and perhaps suppresses parathyroid hormone secretion by the fetus. A unique extrarenal system for 1 alpha-hydroxylation of 25-hydroxyvitamin D3 exists in the placenta and/or decidua, providing a source of 1,25-dihydroxyvitamin D3 for the fetus. With the abrupt cessation of the placental source of calcium at birth, the neonate's serum calcium level falls for 24 to 48 hours, then stabilizes and rises slightly. Hyperparathyroidism during pregnancy causes complications in both mother and infant and should usually be treated surgically as soon as diagnosed. Maternal hypoparathyroidism can be treated satisfactorily with high doses of supplemental calcium and vitamin D. Osteopenia accompanying long-term heparin administration may respond to 1,25-dihydroxyvitamin D3 (calcitriol) therapy. Diabetes in pregnancy is associated with disturbed neonatal calcium homeostasis, perhaps due to chronic hypomagnesemia. A possible etiologic role of calcium deficiency in pregnancy-related hypertension has been suggested. Dietary deficiency of calcium and/or vitamin D during gestation may lead to several adverse effects in the newborn infant.

Correlation between serum ionised calcium and serum albumin concentrations in two hospital populations

One quarter of 172 patients from two hospitals with no obvious disturbances of calcium homeostasis and with total serum calcium concentrations that were normal after adjustment for albumin concentration had low serum ionised calcium concentrations. The low values were not due to changes in pH but were associated with hypoalbuminaemia. Significant positive regressions of ionised calcium on albumin concentration were observed in patients from both hospitals and also in 48 healthy laboratory staff. Because the regressions did not differ between patients and healthy subjects the low ionised calcium values associated with hypoalbuminaemia are unlikely to have been of pathological importance. These findings indicate that interpreting serum ionised calcium concentrations in patients with a reduced serum albumin concentration on the basis of a reference range determined in subjects with a normal serum albumin concentration may be clinically misleading.

Free ionised calcium--a critical survey

It is our aim to summarise and discuss procedures for the evaluation of the concentration of free ionised calcium in serum or plasma. Stress is laid upon the interrelations and relative validity of the most common algebraic expressions to appraise the calcium status. The multitude of formulae proposed in the literature are, by mathematical discussion, reduced to variations on a single theme. A second topic is the direct potentiometric measurement of free ionised calcium concentration. Finally we review the literature on the clinical utility of measuring or calculating the free ionised calcium concentration.

Calcium levels in normal and hypertensive pregnant patients

Epidemiologic studies of hypertension in nonpregnant patients have suggested that abnormal calcium metabolism contributes to the genesis of hypertension. We have studied serum ionized calcium, total calcium, phosphorus, magnesium, total protein, and albumin in 16 normal pregnant women, 12 gravid patients with chronic hypertension, and 31 gravid patients with pregnancy-induced hypertension. In contradistinction to the reported difference in ionized calcium between nonpregnant normal and hypertensive patients, we have found no difference in serum ionized calcium between our groups.

Pregnancy in patients with a porcine valve bioprosthesis

Seven patients who became pregnant after valve replacement with a Hancock bioprosthesis were followed up during 8 pregnancies. Six had undergone isolated mitral valve replacement, and 1 had mitral and aortic valve replacement. Their age at the time of operation ranged from 14 to 31 years (average 24); delivery occurred 21 to 88 months (average 51.3) after valve replacement. All women were in sinus rhythm at the time of gestation, and administration of oral anticoagulants was avoided in all. No embolic episodes occurred either after operation or during pregnancy, labor, or puerperium. The only major complication during pregnancy was cardiac failure in 1 patient, associated with onset of atrial fibrillation. Four women had vaginal delivery and 3 required cesarean section. All but 1 delivered a normal, healthy baby. One premature infant died soon after birth because of respiratory distress. No maternal or fetal hemorrhagic complications were observed. One patient died 3 months after delivery in severe heart failure caused by diffuse calcification of both mitral and aortic xenografts. Another women underwent successful reoperation soon after the second pregnancy because of calcific stenosis of the mitral porcine valve. It is concluded that (1) bioprosthetic valves can be considered the most suitable devices employed in women of childbearing age because anticoagulants can be avoided, therefore eliminating the risks related to inappropriate administration of oral anticoagulants as well as the hazards associated with the potential teratogenic effect of coumarin drugs; and (2) pregnancy might favor calcification of porcine heterografts, leading to bioprosthetic failure. Until further data are available to support this suspicion, close clinical and echocardiographic follow-up study of these patients is recommended after pregnancy.

Clinically significant effect of protein concentration on ion-selective electrode measurements of ionised calcium

Others, using an Orion SS-20 ionised calcium analyser, noted that the ionised calcium concentration of a native serum sample was 8% greater than that of its ultrafiltrate. The experiments described here, using a Nova 2 ionised calcium analyser, confirmed a positive protein interference which was greater for human albumin than for IgG. Uncharged dextran showed no positive interference but dextran sulphate, which is highly charged and binds calcium, showed a large effect. Thus the interference is related to macromolecular charge. Dialysis experiments with normal and pathological human serum samples indicated that the ionised calcium of diffusible plasma water was overestimated by an average of 9.6% at an albumin concentration of 40 g/l and by 4.8% at 20 g/l. It is concluded that the measurement of ionised calcium with existing analysers can be clinically misleading in patients with abnormal plasma proteins. Hypocalcaemia is likely to be overdiagnosed and hypercalcaemia underdiagnosed in the presence of hypoalbuminaemia.

Calcitropic hormone responsiveness during pregnancy

Release of the calcitropic hormones parathyroid hormone (PTH) and calcitonin (CT) in-response to provocative stimuli was assessed in pregnant rhesus monkeys tested three times during gestation (corresponding to the end of each trimester) and again 6 weeks post partum. In the case of PTH, although basal levels were higher during pregnancy than post partum and tended to increase with advancing gestation, similar to observations in human subjects, the incremental response of the hormone to a hypocalcemic stimulus was diminished in pregnant animals and tended to lessen with advancing gestation. Basal CT levels were also increased during pregnancy but, in contrast to PTH, the incremental CT response to a provocative stimulus was generally greater during pregnancy than post partum and tended to increase with advancing gestation. The explanation of these findings may lie in differing degrees of hormone storage. These adjustments in maternal endocrine physiology regulating calcium metabolism would have the net effect of tending to preserve the maternal skeleton by protecting it from excessive resorption at times of hypocalcemia and promoting increased calcium storage during episodes of hypercalcemia.

Ionized calcium in body fluids

This article will review the methods currently available to the clinician and research worker for measuring the concentration of ionized calcium in various body fluids including whole blood, serum, plasma, urine, cerebrospinal fluid, milk, and synovial fluid. The methods to be reviewed are based on procedures involving bioluminescence, colorimetry and ion-selective electrodes. Emphasis will be given to the precision and, wherever possible, accuracy of each technique. Possible sources of error and interfering agents will be identified. Attention will be given to the recommended conditions for measuring ionized calcium in each body fluid. An assessment will be made of the theoretical and practical importance of measuring ionized calcium rather than total calcium and of its value in clinical medicine.

Calcium-regulating hormones and ions in amniotic fluid

Concentrations of the hormones and ions involved in calcium homeostasis were analyzed in simultaneous samples of amniotic fluid and maternal blood obtained from normal pregnant women between 14 weeks' gestation and term. Amniotic fluid total calcium, magnesium, and phosphorus levels fell progressively and markedly despite constant or only declining maternal serum levels. Ionized calcium was constant in both amniotic fluid (mean 2.22 mEq/L) and maternal serum (mean 2.33 mEq/L) throughout gestation. Parathyroid hormone levels in amniotic fluid declined after 20 weeks' gestation, despite rising maternal serum levels, consistent with suppressed fetal parathyroid activity secondary to the relative hypercalcemia of late fetal life. Calcitonin levels in both amniotic fluid and maternal serum were unchanged throughout gestation, with amniotic fluid levels being significantly lower than those in maternal serum.

Calcium measurements in serum and plasma--total and ionized

This article will review the methods currently employed for measuring the concentrations of total and ionized calcium in serum or plasma. As far as total calcium is concerned, various techniques such as atomic absorption spectrometry, spectrophotometry, fluorometry, complexometric titration, and flame photometry will be described and compared. Particular emphasis will be given to the accuracy and precision of each technique. Possible sources of error and interfering agents will be identified and the various procedures for the taking and handling of blood samples evaluated. Inter-laboratory variation in the measurement of calcium will be studied. An assessment will be made of a new reference method for measuring total calcium in serum using isotope-dilution mass spectrometry. The usefulness of the total calcium measurement in clinical medicine will be briefly discussed. Within the last decade the refinement of spectrophotometric techniques and the improvements in ion-selective electrode technology have revolutionized the measurement of ionized calcium in serum, such that it may now be possible to replace total calcium measurements with ionized calcium measurements on a routine basis. The various techniques currently in use for measuring ionized calcium will be described and evaluated. Particular attention will be paid to the preparation of standards, the procedures for taking blood samples, and the handling of the samples prior to and during measurement. An assessment of the relative value of measuring total and ionized calcium will be presented.

Effects of magnesium sulfate treatment on perinatal calcium metabolism. I. Maternal and fetal responses

Serial maternal and cord blood determinations of the ions and hormones involved in calcium homeostasis were made in pre-eclamptic women treated with intravenous magnesium sulfate. A 4 gm loading dose followed by 1 to 2 gm/hr caused maternal serum magnesium concentrations to rise 150%, to levels of 3.3 to 4.5 mEq/L, and ionized calcium levels to fall 16%, to 1.89 mEq/L. The hypocalcemia etly altering calcitonin. Changes in total calcium paralleled those of ionized calcium; phosphorus levels were not affected by magnesium infusion. At the time of delivery the offspring of these women were hypermagnesemic and relatively hypocalcemic, although less so than their mothers. Fetal ionized calcium levels, although lower with magnesium treatment than in control subjects, were within the lower limits of the normal range, which perhaps explains why the fetus did not respond with increased PTH or decreased calcitonin output. These results indicate that the principal maternal response to magnesium-induced hypocalcemia involves increased parathyroid hormone secretion which tends to preserve maternal calcium homeostasis, while the fetus is partially protected from hypermagnesemia and hypocalcemia by the placenta.

Calcium metabolism in normal pregnancy: a longitudinal study

Total and ionic calcium, magnesium, phosphorus, albumin, and immunoreactive parathyroid hormone (iPTH) and calcitonin (iCT) were measured in serum or plasma from 30 women throughout pregnancy (beginning before 12 weeks' gestation) and the puerperium. Total calcium levels declined during gestation, paralleling a progressive fall in albumin concentration, whereas ionic calcium values declined only very slightly. Although iPTH levels in early pregnancy were lower than postpartum values (suggesting that iPTH may decline initially following conception), the major portion of gestation was characterized by progressively increasing concentrations which at term averaged 53% above early pregnancy levels and 33% above puerperal values. Thus, the principal adjustment during pregnancy is "physiologic hyperparathyroidism" which acts to preserve maternal homeostasis by maintaining the concentration of calcium ions in extracellular fluid in the presence of expanding fluid volume, increased renal function, and placental transfer. iCT levels were not affected consistently by pregnancy and exhibited highly variable patterns; half of the subjects demonstrated an increase during the first and second trimesters and then a decline in the third trimester and the remaining half was equally divided between those with no change and those with progressively falling levels.