Serum ionic calcium levels during pregnancy

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.

Calciotropic hormones during reproduction

This review summarizes the reported effects of the menstrual cycle, pregnancy and lactation on serum concentration of the calciotropic hormones PTH and 1,25(OH)2D. A midcycle rise in PTH and 1,25(OH)2D has been observed, but in the majority of studies there was no change in PTH and 1,25(OH)2D concentrations throughout the menstrual cycle. Both total and free 1,25(OH)2D levels are increased during pregnancy. The renal 1,25(OH)2D production is stimulated, and there is some evidence of 1,25(OH)2D production by decidua/placenta and fetal kidney in vitro; the decidual/placental production should not be overestimated in vivo. The increased renal 1 alpha-hydroxylase activity is possibly mediated by estrogens and PTH, although the effect of pregnancy on PTH remains uncertain. Increased serum 1,25(OH)2D concentrations probably result in a rise of intestinal calcium absorption during pregnancy. There is a postdelivery drop in PTH and 1,25(OH)2D levels, but they are increased when lactation is prolonged, or in mothers nursing twins. The l alpha-hydroxylase activity during lactation may be stimulated by PTH, but also by prolactin.

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.

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.

Urinary and plasma vitamin D3 metabolites in the nephrotic syndrome

Using newly developed and established extraction, Lipidex-5000 chromatography, normal phase gradient HPLC, and ligand binding assay techniques we have directly measured plasma and urine levels of vitamin D3 and its metabolites in seven normal subjects and seven patients with nephrotic syndrome and normal renal function. Significant reductions in the plasma levels of vitamin D3, 24,25(OH)2D3, 25,26(OH)2D3, and 1,25(OH)2D3 were noted in all nephrotic patients. In conjunction with the plasma metabolite abnormalities, direct quantitative analysis of the urine in these patients revealed significant increases in nonconjugated 250HD3, 24,25(OH)2D3 and 1,25(OH)2D3. Significant correlations were noted between the plasma and/or urine metabolites and other mineral homeostatic parameters. The results indicate that the primary basis for the reductions in plasma vitamin D3 and its metabolites in the nephrotic syndrome is enhanced urinary excretion. The findings of normal serum ionized Ca and i-PTH levels in the patients with nephrosis suggest that reductions in bound and not free forms of vitamin D3 metabolites in plasma may occur in the initial stages of the nephrotic syndrome.

Influence of the vitamin D-binding protein on the serum concentration of 1,25-dihydroxyvitamin D3. Significance of the free 1,25-dihydroxyvitamin D3 concentration

The influence of the serum binding protein (DBP) for vitamin D and its metabolites on the concentration of its main ligands, 25-hydroxyvitamin D(3) (25-OHD(3)) and 1,25-dihydroxyvitamin D(3) (1,25-[OH](2)D(3)) was studied. The concentration of both 1,25-(OH)(2)D(3) and DBP in normal female subjects (45+/-14 ng/liter and 333+/-58 mg/liter, mean+/-SD, respectively; n = 58) increased during the intake of estro-progestogens (69+/-27 ng/liter and 488+/-90 mg/liter, respectively; n = 29), whereas the 25-OHD(3) concentration remained unchanged. A positive correlation was found between the concentrations of 1,25-(OH)(2)D(3) and DBP in these women. At the end of pregnancy, the total concentrations of 1,25-(OH)(2)D(3) (97+/-26 ng/liter, n = 40) and DBP (616+/-84 mg/liter) are both significantly higher than in nonpregnant females and paired cord serum samples (48+/-11 ng/liter and 266+/-41 mg/liter, respectively). A marked seasonal variation of 25-OHD(3) was observed in pregnant females and their infants, whereas in the same samples the concentrations of both DBP and 1,25-(OH)(2)D(3) remained constant throughout the year. The free 1,25-(OH)(2)D(3) index, calculated as the molar ratio of this steroid and DBP, remains normal in women taking estro-progestogens, however, and this might explain their normal intestinal calcium absorption despite a high total 1,25-(OH)(2)D(3) concentration. In pregnancy the free 1,25-(OH)(2)D(3) index remains normal up to 35 wk of gestation, but during the last weeks of gestation, the free 1,25-(OH)(2)D(3) index increases in both circulations. A highly significant correlation exists between the (total and free) 25-OHD(3) and 1,25-(OH)(2)D(3) concentrations in maternal and cord serum both at 35 and 40 wk of gestation.

Biochemical changes of normal pregnancy and puerperium in Lagos, Nigeria

A cross-sectional study is presented of biochemical changes in the third trimester of normal pregnancy and puerperium during the wet season in the tropical climate of Lagos, Nigeria. These changes are less marked in first than in subsequent pregnancies, and although qualitatively similar, in some respects they differ from those observed in the temperate climatic zone. The indications are that quantitative differences may exist which could be relevant to the management of pregnancy in the tropics.

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.

Serum calcium concentrations in human pregnancy

Total and ionic calcium concentrations were measured in maternal serum from nonpregnant (N=30), pregnant (N=137), and early puerperal (N=17) women. In this cross-sectional study, total calcium levels (measured by atomic absorption spectrophotometry) exhibited the previously described pattern of a decline beginning in the first trimester and continuing until approximately 32 weeks, with a slight terminal rise from thence to term. Mean (+/-SD) values for the three trimesters were 4.80 (+/- 0.13), 4.56 (+/- 0.14), and 4.46 (+/-0.16) mEq. per liter, respectively, with all differences statistically significant. Ionic calcium levels (measured by calcium flow-through electrode) declined to a lesser (though still statistically significant) degree; mean (+/- S.D.) values for the three trimesters were 2.33 (+/-0.07), 2.28 (+/-0.08), and 2.24 (+/-0.06) mEq. per liter, respectively. Because of the differential rates of fall, the proportion of total calcium represented by the ionic component increased progressively during gestation. The results indicate that the major portion of the characteristic decline in maternal serum total calcium concentration with pregnancy reflects changes in the nonionized (albumin-bound) fraction while the ionic portion declines only slightly. The concentration of calcium ions in serum is maintained within a very narrow physiologic range throughout gestation.

Altered vitamin-D metabolism in pregnancy

Low levels of plasma-25-hydroxy-vitamin-D (25-OHD) (less than 16 nmol/1) were found in 33% of a group of pregnant women studied in South London. Non-White women in the last 10 weeks of pregnancy had significantly reduced levels compared with non-pregnant controls (P less than 0.02). Plasma-25-OHD was unrelated to dietary vitamin-D intake, age, parity, social class, plasma-calcium, and plasma-albumin. Reduction of plasma-25-OHD could contribute to the fall in plasma-calcium during pregnancy, and may result from enhanced maternal metabolism or increased utilisation of vitamin D by the fetus.

Hyperparathyroidism during pregnancy

Hyperparathyroidism during pregnancy is clearly associated with an increased incidence of neonatal morbidity and mortality. Although it is impossible to define the precise incidence of this entity, we believe that its occurrence will be seen more frequently with the increasing numbers of female patients who have successfully received renal transplants and with the routine determination of serum chemistries in the nontransplanted pregnant patient. A review of case reports since 1962 of women known to be hyperparathyroid during pregnancy revealed 80 per cent of these pregnancies to be complicated by neonatal tetany, death, or abortion. This review substantiates Ludwig's earlier report [1], which noted a 50 per cent incidence of neonatal complications despite the advances of prenatal and postnatal medical care. There have been only eight reported cases in which parathyroid resection was performed during pregnancy. Successful operation dramatically reduced the incidence of neonatal complications. An adaptive normocalcemic hyperparathyroidism occurs routinely during pregnancy. However, in the hypercalcemic hyperparathyroid pregnancy, transplacental passage of calcium leads to a profound hypercalcemia in the fetus. Since the fetal parathyroid glands are functionally responsive, parathyroid suppression is thought to occur in utero due to high calcium levels. This can lead to neonatal tetany or perhaps permanent neonatal hypoparathyroidism. When a patient presents with significant hypercalcemic hyperparathyroidism during pregnancy, we suggest that an explorative parathyroid operation be performed during the second trimester of pregnancy. After delivery, the baby's course should be carefully monitored with frequent calcium determinations. Cow's milk or other formula feedings high in phosphate content should be avoided in favor of feedings with a calcium:phosphorus ratio similar to that of human milk.

Recent advances in calcium metabolism. I. Mechanisms of calcium homeostasis

Within recent years newly acquired knowledge has provided a clearer understanding of some aspects of the complex mechanisms that collectively maintain calcium homeostasis within body fluids and it is our intent to define current concepts of the interrelationship of these various factors to the end that fuller understanding may be available concerning the maintenance of calcuim homeostasis in health as well as features which result in its disruption and the consequent effects of imbalances of calcium in various disease states. In this first section dealing with the physiologic state, there are included descriptions of: (1) the metabolism of vitamin D, the synthesis of its active metabolites, 25 OHD3 and1.25(OH)2D3, and the metabolic actions of the active vitamin D metabolite and analogues upon gastrointestinal, bone, and kidney functions; (2) the synthesis, secretion, and metabolic activity of parathyroid hormone and the difficulties with the radioimmunoassay of PTH related to the number of PTH-like peptides in the circulation; and (3) the chemistry, metabolism, and biologic activities of calcitonin, a hypocalcemic principle derived from the parafollicular cells of the thyroid gland. It is emphasized that under normal circumstances these humoral mechanisms act in an integrated manner to maintain serum concentrations of total and ionized calcium within narrowly defined limits.

Serum calcium, phosphorus and magnesium levels in pregnant and non-pregnant Nigerians

Serum calcium, inorganic phosphorus and magnesium were determined in 282 Nigerian women comprising 213 pregnant women, 37 non-pregnant controls, and 32 postpartum women. There was very little change in the serum calcium levels throughout pregnancy; the slight reduction which occurred during the 8th and 9th months was not statistically significant. There was a significant reduction in the serum concentrations of inorganic phosphorus and magnesium during the 8th and 9th months of gestation; the levels of both minerals rose to non-pregnant levels at term.

Calcium metabolism in pregnancy: a review

Calcium metabolism in pregnancy is a complex process involving calcium, phosphorus, vitamin D, parathyroid hormone (PTH), and calcitonin (CT). Calcium absorption is enhanced in pregnancy, and increased storage in the maternal skeleton probably occurs as well. Adequate amounts are provided by the current Recommended Dietary Allowance of 1,200 mg. daily which can be met readily by natural foods, specifically milk. If supplemental calcium is given, a nonphosphate salt is probably advisable, since some evidence suggests that excessive phosphate intake may be related to leg cramps in pregnancy. Vitamin D is necessary for optimal calcium utilization in pregnancy, although the possibility of fetal toxicity with overdosage has been suggested. From a review of available information with respect to maternal-perinatal calcium interrelationships, I propose the following hypothesis: While total maternal serum calcium declines during pregnancy because of the physiologic hypoalbuminemia, the level of ionic calcium remains constant, in part, at least, because of increasing maternal PTH output. The placenta plays a primary role in fetal calcium metabolism by transporting calcium ions from the mother to the fetus against a concentration gradient. Relatively high fetal ionic calcium levels cause suppression of PTH and stimulation of CT in the fetus, facilitating growth of the fetal skeleton. With sudden loss of the placental source of calcium at birth, the newborn infant becomes functionally hypoparathyroid and/or hypercalcitonemic, and the serum calcium level declines until 3 to 4 days of life when PTH rises and CT falls with a resultant slight rise in calcium.

Calcium metabolism in newborn infants. The interrelationship of parathyroid function and calcium, magnesium, and phosphorus metabolism in normal, "sick," and hypocalcemic newborns

Serum immunoreactive parathyroid hormone (iPTH) and plasma total calcium, ionized calcium, magnesium, and phosphorus levels were determined during the first 9 days of life in 137 normal term infants, 55 "sick" infants, and 43 hypocalcemic (Ca <7.5 mg/100 ml; Ca(++)<4.0 mg/100 ml) infants. In the cord blood, elevated levels of plasma Ca(++) and Ca were observed, while levels of serum iPTH were either undetectable or low. In normal newborns during the first 48 h of life there was a decrease in plasma Ca and Ca(++), while the serum iPTH level in most samples remained undetectable or low; after 48 h there were parallel increases in plasma Ca and Ca(++) and serum iPTH levels. Plasma Mg and P levels increased progressively after birth in normal infants. In the sick infants, plasma Ca, Ca(++) and P levels were significantly lower than in the normal newborns, while no significant differences were found in the plasma Mg levels. The general pattern of serum iPTH levels in the sick infants was similar to that observed in the normal group, though there was a tendency for the increase in serum iPTH to occur earlier and for the iPTH levels to be higher in the sick infants. In the hypocalcemic infants, plasma Mg levels were consistently lower than in the normal infants after 24 h of age, while no significant differences were found in the plasma P levels. Hyperphosphatemia was uncommon and did not appear to be a contributing factor in the pathogenesis of hypocalcemia in most infants. Most of the hypocalcemic infants, including those older than 48 h, had inappropriately low serum iPTH levels. Evidence obtained from these studies indicates that parathyroid secretion is normally low in the early new born period and impaired parathyroid function, characterized by undetectable or low serum iPTH, is present in most infants with neonatal hypocalcemia. Additional unknown factors appear to contribute to the lowering of plasma Ca in the neonatal period. The net effect of unknown plasma hypocalcemic factor(s) on the one hand and parathyroid activity on the other may account for differences in plasma Ca levels observed between normal, sick, and hypocalcemic infants. Depressed plasma Mg is frequently present in hypocalcemic infants. To what degree the hypomagnesemia reflects parathyroid insufficiency or the converse, to what degree parathyroid insufficiency and hypocalcemia are secondary to hypomagnesemia, is uncertain.