Hypocalciuria in preeclampsia

Calciuria in symptom-free primigravid women remote from term: is the response to an oral calcium challenge predictable?

OBJECTIVE

This study was undertaken to compare the calciuric response in symptom-free primigravid women to an oral calcium load between those with normal urinary calcium excretions and those with relatively low urinary calcium excretions.

STUDY DESIGN

This was a prospective clinical trial. Eligible primigravid women between 16 and 20 weeks' gestation provided a 24-hour urine sample for determination of urinary calcium/urinary creatinine ratio. On the basis of these results the patients were divided into 2 groups: a relatively hypocalciuric group, in which the urinary calcium excretion was </=3.4 mg. kg-1. 24 h-1, and a normocalciuric group, in which the urinary calcium excretion was >3.4 mg. kg-1. 24 h-1. All participants undertook a 3-day low calcium dietary regimen. On the fourth day women underwent an oral calcium challenge. A 2-hour urine sample was collected before ingestion of 1 g calcium carbonate (preload). One hour after ingestion the women again collected a 2-hour urine sample (postload). The urinary calcium/urinary creatinine ratios in the preload and postload samples were determined and compared within and between the groups.

RESULTS

The mean change (+/-SD) between the preload and postload urinary calcium/urinary creatinine ratios in the relatively hypocalciuric group was 0.60 +/- 1.44 (P =.04); that in the normocalciuric group was 3.09 +/- 2.26 (P =.11 ). There was a 5-fold difference in the response to calcium load between the hypocalciuric women and the normocalciuric women (0.60 vs 3.09), although this difference was not statistically significant (P =.20).

CONCLUSIONS

Both hypocalciuric and normocalciuric women responded to an oral calcium challenge by an increase in the calcium excretion. The cause of the hypocalciuria in women at increased risk for preeclampsia is therefore not simply poor absorption of calcium.

Lymphocyte intracellular free calcium concentration is increased in preeclampsia

OBJECTIVES

We tested 2 hypotheses: (1) Preeclampsia is characterized by an increase in intracellular free calcium concentration in lymphocytes. (2) Levels of intracellular free calcium are influenced by the calcium concentration in the extracellular milieu or by parathyroid hormone.

STUDY DESIGN

Intracellular free calcium concentrations were measured in 4 groups of women: nonpregnant women (n = 25), normotensive pregnant women (n = 30), pregnant women with chronic hypertension (n = 15), and women with preeclampsia (n = 15). Intracellular free calcium concentration was measured in the basal state, at varying extracellular calcium ion concentrations, and in the presence of exogenous parathyroid hormone.

RESULTS

Women with preeclampsia had the highest basal lymphocyte intracellular free calcium concentration (121 +/- 7 nmol/L, mean +/- SEM) compared with normotensive pregnant women during the third trimester (94 +/- 3 nmol/L, P <.001) and pregnant women in the third trimester with chronic hypertension (100 +/- 3 nmol/L, P <.01). During the third trimester normotensive women and women with chronic hypertension had significantly higher basal intracellular free calcium concentrations than were found in women during the first trimester. Exposure of lymphocytes to an extracellular milieu of low calcium concentration resulted in an increase in intracellular free calcium concentration. Incubation with parathyroid hormone had no effect on intracellular free calcium concentration.

CONCLUSIONS

Lymphocyte intracellular free calcium concentration is increased in preeclampsia and not in chronic hypertensive pregnancy and is greater during the third trimester than during the first trimester. Extracellular calcium depletion increases lymphocyte intracellular free calcium concentration. These data support the idea that a calcium deficit leading to an increased intracellular free calcium concentration during late pregnancy contributes to the pathogenesis of preeclampsia.

Prevention of preeclampsia

Preeclampsia is a multisystem disorder of unknown cause. Efforts to prevent the disease or reduce its incidence have utilized pharmacological intervention as well as dietary supplementation. Recent, large, randomized trials have not shown a benefit from the use of aspirin. Calcium supplementation has also been studied extensively and found to be similarly ineffective in reducing the incidence or severity of preeclampsia in healthy women. The studies regarding the use of magnesium, zinc, and fish oils for the prevention of preeclampsia are fewer in number, but have also found minimal to no benefit. In the same respect, numerous randomized trials have been performed using antihypertensive agents, diuretics, and low-salt diet. Results of these studies have not shown any beneficial effect. Prevention of preeclampsia is unlikely as long as the underlying origin remains unknown.

Pregnancy in SLE

The effect of pregnancy on disease activity in systemic lupus erythematosus remains controversial. Studies on lupus flares in pregnancy are discussed, including prospective data on severity of flares and organ involvement from the Hopkins Lupus Pregnancy Center. The major fetal concerns of miscarriage (due to the antiphospholipid antibody syndrome), pre-term birth (largely due to pre-eclampsia or premature rupture of membranes) and neonatal lupus, are reviewed.

Urinary calcium/creatinine ratio as a predictor of preeclampsia

Hypocalciuria has been associated with preeclampsia (gestational hypertension with proteinuria or other maternal organ dysfunction) but not usually with pure gestational hypertension or normal pregnancy. We hypothesized that hypocalciuria would be a marker of emerging preeclampsia in women presenting with gestational hypertension who later developed preeclampsia. Eighty-one women with de novo hypertension in the second half of pregnancy (n = 81) were enrolled prospectively. At first assessment, calcium/creatinine ratio was determined in a spot urine. Patients were followed until delivery and were classified subsequently according to the occurrence of preeclampsia. Gestational hypertensive patients who became preeclamptic (n = 31) had lower urinary calcium/creatinine ratios at presentation (ratio = 0.07, interquartile range [IQR] = 0.04-0.11) than women who remained as gestational hypertensives (n = 50; ratio = 0.17, IQR = 0.08-0.21; P = .002). Intact plasma parathyroid hormone (PTH) concentrations were similar between groups. Using a receiver operator curve, the best threshold value for the development of preeclampsia was a calcium/creatinine ratio of 0.10, which yielded a sensitivity of only 68% and a specificity of 70%. A low calcium/creatinine ratio preceded the emergence of preeclampsia by 12 (7-24) (median [IQR]) days among a group of women with gestational hypertension. Though this implies primary or secondary disturbances of renal calcium handling even before preeclampsia is clinically apparent, this measurement does not have sufficient sensitivity to recommend its use as a screening test for the emergence of preeclampsia.

Calciuria and preeclampsia

Urinary calcium excretion has been reported to be diminished in preeclampsia. The objective of the present study was to determine urinary calcium excretion in pregnant patients with chronic arterial hypertension (CAH) and preeclampsia (PE), and in normotensive patients (N). Forty-four pregnant patients (gestational age, 20-42 weeks; 18 CAH, 17 PE, 9 N) were evaluated for calciuria, proteinuria, plasma uric acid and blood pressure. Patients with PE (82 +/- 15.1 mg/24 h) showed significantly lower calciuria (P < 0.05) than the group with CAH (147 +/- 24.9 mg/24 h) and the N group (317 +/- 86.0 mg/24 h) (P < 0.05, Student t-test). Plasma uric acid was significantly higher in the PE group (6.1 +/- 0.38 mg/dl) than the CAH group (5.0 +/- 0.33 mg/dl; P < 0.05), which also presented higher proteinuria levels, although the difference was not statistically significant. Diastolic and systolic blood pressure did not differ between the PE (164 +/- 105 mmHg) and CAH (164 +/- 107 mmHg) groups. Calciuria was significantly lower in the group with preeclampsia than in the group with chronic arterial hypertension. We conclude that calciuria can be a further factor for identifying preeclampsia.

Predicting high blood pressure in pregnancy: a multivariate approach

OBJECTIVE

To identify predictors of pregnancy-induced hypertension and pre-eclampsia in 212 nulliparous women before 20 weeks' gestation and at approximately 28 weeks' gestation.

STUDY DESIGN

A randomized, prospective study in a teaching hospital. We performed standardized measurements of systolic and diastolic arterial blood pressures, body mass index, urinary calcium:creatinine ratio and components of the renin-angiotensin system, including platelet angiotensin II binding site density. Attending clinicians were blinded to the results. Outcome was assessed by one observer at the end of pregnancy. Discriminant function analysis was used to identify significant predictors.

RESULTS

Fifty-five women had transient, presumed 'white-coat', systolic hypertension at the time of first pregnancy visit; they were twice as likely to develop pregnancy-induced hypertension and pre-eclampsia and five times more likely to deliver prematurely. Body mass index, platelet angiotensin II binding site density and urinary calcium:creatinine ratio measured before 20 weeks gestation were also significant predictors. At 28 weeks of pregnancy, measurements of the blood pressure were significant predictors (reflecting the near clinical expression of the disease), together with the plasma angiotensinogen concentration.

CONCLUSIONS

A single systolic blood pressure reading of 140 mmHg or more before 20 weeks' gestation indicates a higher than normal risk of pregnancy-induced hypertension and pre-eclampsia and premature delivery. Discriminator biochemical variables were also identified at this time, which might allow the more rational use of prophylactic measures.

Calcium-to-creatinine ratio in spot urine samples in early pregnancy and its relation to the development of preeclampsia

We investigated the relation between an alteration in calcium (Ca) excretion in early pregnancy and the risk of preeclampsia in 1,147 pregnant women. We measured Ca and creatinine (Cr) concentrations in spot urine samples obtained at 12 weeks or less of gestation. Seventy-one (6.2%) had hypertension alone, nine (0.8%) developed superimposed preeclampsia, 39 (3.4%) developed proteinuria alone, and 13 (1.1%) developed preeclampsia; 1,015 women did not develop hypertension or proteinuria. The Ca/Cr ratio was significantly reduced in the 39 women who eventually developed proteinuria (0.116 +/- .103) and 13 who developed preeclampsia (0.121 +/- .063) compared with 1,015 women who had neither hypertension nor proteinuria (0.158 +/- .239). The relative risk of development of preeclampsia, proteinuria, or superimposed preeclampsia was 1.98 (95% confidence interval, 1.22 to 3.22) for women with a Ca/Cr ratio less than the 30th percentile (0.082) compared with women with a Ca/Cr ratio greater than the 30th percentile. These results suggest that preeclampsia may be related, in part, to a relative Ca intake deficiency. Determination of the Ca/Cr ratio in spot urine samples in the first trimester is of only limited clinical value for identifying women with an increased risk of preeclampsia.

Obstetric management of the high-risk lupus pregnancy

With improvements in diagnosis and treatment, the prognosis of patients with systemic lupus erythematosus has generally improved in recent years, and similarly the outlook for women who become pregnant in the setting of this disorder is far more optimistic than it once was. The risk of significant morbidity to both the mother and fetus exists, however. Beginning with preconception counseling, a careful and thorough approach to the care of the patient and cooperation among her various health care providers optimizes the chance of a successful pregnancy.

Trial of Calcium for Preeclampsia Prevention (CPEP): rationale, design, and methods

The results of ten clinical trials suggest that supplemental calcium may prevent preeclampsia. However, methodologic problems and differences in study design limit the acceptance of the results and their relevance to other patient populations. Many of the trials were conducted in countries where, unlike the United States, the usual daily diet contained little calcium. Moreover, none of the trials has reported the outcome of systematic surveillance for urolithiasis, a potential complication of calcium supplementation. In response to the need for a thorough evaluation of the effects of calcium supplementation for the prevention of preeclampsia in the United States, the trial of Calcium for Preeclampsia Prevention (CPEP) was undertaken at five university medical centers. Healthy nulliparous patients were randomly assigned to receive either 2 g supplemental calcium daily (n = 2295) or placebo (n = 2294) in a double-blind study. Study tablets were administered beginning from 13 to 21 completed weeks of gestation and continued until the termination of pregnancy. CPEP employed detailed diagnostic criteria, standardized techniques of measurement, and systematic surveillance for the major study endpoints and for urolithiasis. The nutrient intake of each patient was assessed at randomization and at 32-33 weeks gestation. This report describes the study rationale, design, and methods.

Calcium supplementation and prevention of pregnancy induced hypertension

In a randomized controlled trial 201 healthy nulliparous women were randomly allocated by means of a computer generated randomization list. From 20 weeks of gestation until delivery they received either 2 g of oral elemental calcium (n = 103) per day or an identical placebo (n = 98). Eleven women (5.47%) were lost to follow-up after randomization. The study groups were very similar at the time of randomization; with respect to several clinical and demographic variables. Treatment compliance was very similar in both groups as was determined by pill count. The rate of pregnancy induced hypertension was lower in the calcium group than in the placebo group 8.24%; vs 29.03%; (RR = 0.28; 95% CI 0.14-0.59). The incidence of gestational hypertension was 6.18% in the calcium group and 17.20% in the placebo group (RR = 0.28; 95% CI 0.08-0.80), and the incidence of preeclampsia was 2.06% in the calcium group and 11.82% in the placebo group (RR = 0.13; 95% CI 0.01-0.64). In conclusion calcium supplementation given in pregnancy to nulliparous women reduces the incidence of pregnancy induced hypertension.

Values of certain clinical and biochemical tests for prediction of pre-eclampsia

To evaluate different predictive tests for pre-eclampsia, either individually or in combination, we prospectively studied 100 primigravid females. Eighty-eight of the subjects continued the follow-up until delivery and 17 developed pre-eclampsia. Venous blood samples were take for determination of plasma fibronectin, and urine samples were taken for determination of microalbuminaria and calcium-creatinine ratio. Isometric handgrip exercise tests were also performed. Evaluation of predictive tests, as well as t and chi-squared statistical tests, were used for analysis of data. Pre-eclampsia developed in 19.3% of the patients studied. Pre-eclamptic and normotensive females showed significant differences in calcium-creatinine ratio and plasma fibronectin levels in both ( 14-24 weeks and 28-32 weeks) gestation periods (P <.0001). Plasma fibronectin had the best sensitivity, positive, and negative values in gestation period 14-24 weeks, whereas isometric handgrip exercise tests had the best specificity. These values improved for all the tests in the 28-32-week gestation period; even so, plasma fibronectin proved best of all. A combination of tests failed to improve the predictive ability of fibronectin alone. We conclude that plasma fibronectin is the best predictive test for pre-eclampsia.

The physiology of pre-eclampsia

1. Pre-eclampsia is a multisystem disorder of human pregnancy with a genetic predisposition. It occurs more commonly in first pregnancies and primarily affects maternal renal, cerebral, hepatic and clotting functions while elevating blood pressure. The foetus is affected through placental insufficiency arising from abnormal 'placentation', that is, failure to adequate trophoblast invasion of maternal vasculature, and possible from abnormal autacoid production. 2. Pre-eclampsia is caused by the placenta; delivery of the placenta is the only known cure. Its manifestations are considered secondary to organ hypoperfusion which arises as a result of vasoconstriction, intravascular coagulation and reduced maternal blood volume. 3. Current hypotheses propose that pre-eclampsia is due to widespread maternal endothelial cell damage, perhaps secondary to a cytotoxic factor released by the placenta. This hypothesis has gained wide acceptance, but scientific evidence is lacking. 4. Defining the abnormal balance of vasoactive factors in pre-eclampsia has proved a difficult task. There is enhanced pressor activity to infused angiotensin II (AII) despite reduced plasma concentrations of AII, renin and aldosterone. Prostacyclin production appears reduced, and the balance of thromboxane/prostacyclin favours vasoconstriction and platelet aggregation. There is no convincing evidence for enhanced endothelin or reduced nitric oxide production. Plasma concentrations of atrial natriuretic peptide are paradoxically elevated in the face of plasma volume contraction. An intriguing observation, which remains unexplained, is why some vascular beds are affected predominantly in one patient (eg. hepatic ischaemia) while another has a similar degree of hypertension but involvement of a different organ system (eg. renal insufficiency yet normal liver function). 5. Volume homeostasis is disturbed with redistribution of intravascular volume to the interstitial fluid space due to increased capillary permeability and in some cases reduced plasma oncotic pressure. This redistribution is not always clinically apparent as peripheral oedema. Whether this change in volume is compensated for by venoconstriction and maintenance of adequate cardiac output is undetermined. 6. Improved understanding of the pathophysiology of pre-eclampsia is necessary to allow better clinical management of this serious disorder.

Intraplatelet free calcium and calcium-regulating hormones in plasma are not related to the antihypertensive effect of nifedipine in hypertensive pregnancy

Intracellular free calcium regulates contraction-relaxation processes in vascular smooth muscle. We compared intraplatelet free calcium ([Ca2+]i) and pH ([pH]i) in hypertensive pregnant women to those in normotensive pregnant and non-pregnant women. Plasma parathormone and vitamin D metabolite were simultaneously assessed. In hypertensive pregnancy, [Ca2+]i tended to be lower than in normotensive pregnant (P = 0.08) and non-pregnant subjects (P = 0.06). In hypertensive pregnancy, 1,25, (OH)2 vitamin D in plasma was in the same range as in non-pregnant women and significantly lower than in normotensive pregnancy (p < 0.01). The other two vitamin D metabolites, parathormone and [pH]i were equal in the three groups. A five-day nifedipine treatment (10 mg t.i.d.) increased [Ca2+]i in hypertensive pregnant (P < 0.05) and normotensive non-pregnant subjects (P = 0.06), whereas [pH]i (P < 0.05) and 25 (OH) vitamin D (P < 0.05) decreased in the former and 24,25 (OH)2 vitamin D increased in the latter group (P < 0.05). Initial [Ca2+]i did not correlate with blood pressure in any group. The antihypertensive effect of nifedipine did not correlate with any variable measured. In conclusion, [Ca2+]i and calcium-regulating hormones seem not to be related to the antihypertensive effect of nifedipine in hypertensive pregnancy. In this type of hypertension, intraplatelet calcium may not reflect calcium balance in smooth muscle cells regulating vascular tone and blood pressure.

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.

Pre-eclampsia: excessive activation of a G protein-associated receptor?

Although the systemic physiological alterations present in pre-eclampsia appear disparate and unrelated, four of them (endothelial cell hyperplasia and alterations in uric acid, calcium, and prostaglandin homeostasis) are demonstrated here to mimic closely the pattern of intracellular alterations caused by the activation of a G protein-associated receptor. The implication of this is that the excessive activation of a particular G protein-associated receptor may play a central role in the pathogenesis of pre-eclampsia.

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.

The laboratory evaluation of hypertensive gravidas

A number of laboratory tests are available for the evaluation of the hypertensive gravida. These tests can be used to either predict and/or prognosticate between preeclampsia and other hypertensive disorders of pregnancy. These laboratory tests were evaluated based on published experience with special attention to its ability to facilitate identification of the patient with preeclampsia apart from other hypertensive disorders that co-exist with and occur as a complication of pregnancy. Hypocalciuria and increased cellular plasma fibronectin seem to be good tests to differentiate preeclampsia from chronic hypertension. The management of preeclampsia with its increased risk of perinatal morbidity and mortality renders this differentiation clinically very important. Hyperuricemia, proteinuria, increased serum beta-thromboglobulin concentration, abnormal red blood cell morphology with increased hemoglobin/hematocrit, and increased serum iron individually and collectively reflect the severity of preeclampsia. Platelets and total serum lactate dehydrogenase are the best tests to reflect the severity of HELLP syndrome. Circulating hCG and serum thromboglobulin seem to be the most promising future predictors for preeclampsia.

Increased amniotic fluid divalent cation concentration in preeclampsia

Hypocalciuria due to reversibly enhanced tubular calcium reabsorption in preeclampsia has been previously described. As the fetus is exposed in utero to the toxemic environment, its kidney function may be similarly affected. We therefore evaluated the amniotic fluid (AF) concentrations of Ca2+, Mg2+, Zn2+, and Na+ in relation to creatinine in 12 preeclamptic women, 9 pregnant women with chronic hypertension, and 12 control pregnant women. Our data reveal an increased AF Ca2+, Mg2+, and Zn2+ to creatinine ratio in preeclampsia 451 +/- 283; 164 +/- 94; 787 +/- 124 Eq/mol, respectively) as compared with chronic hypertension (256 +/- 141; 94 +/- 46; 504 +/- 124 Eq/mol, respectively), and normal controls (274 +/- 132; 83 +/- 19; 477 +/- 124 Eq/mol, respectively; p < 0.05). Na+ concentration did not vary significantly among the three groups. It is suggested that the higher AF divalent cation concentration in preeclampsia may be due to lower maternal urinary excretion thereby increasing the fetal divalent cation load.

Prevention of preeclampsia with calcium supplementation and vitamin D3 in an antenatal protocol

OBJECTIVES

Using an angiotensin sensitivity test we carried out a prospective study in an attempt to predict the possible onset of preeclampsia and to prevent it by calcium supplementation (elemental calcium 156 or 312 mg/day per os) and treatment with vitamin D3 (0.5 micrograms/3 day per os).

METHOD

We used a study design in which 666 singleton pregnant women were managed with conventional antenatal care and 210 singleton pregnant women were managed with a protocol, together with conventional antenatal care.

RESULT

Of the 666 women managed conventionally, 113 (16.9%) developed preeclampsia. However, the incidence of preeclampsia in the 210 women managed on the protocol was lower, at 10.9%.

CONCLUSION

Our findings indicate that this protocol for the prediction and prevention of preeclampsia is useful for pregnant women at high risk of developing preeclampsia.

Atrial natriuretic peptide and cyclic guanosine-3'5'-monophosphate in hypertensive pregnancy and during nifedipine treatment

Atrial natriuretic peptide exhibits natriuretic, diuretic and vasodilatory properties. We compared plasma concentrations of atrial natriuretic peptide, cyclic guanosine-3',5'-monophosphate (cGMP), electrolytes and urinary excretion of cGMP and electrolytes in hypertensive pregnant women to those in normotensive pregnant and normotensive non-pregnant women. Plasma atrial natriuretic peptide concentrations in hypertensive pregnant and normotensive non-pregnant women were equal, whereas in normotensive pregnant women it was lower (P < 0.05), than in non-pregnant. Urinary cGMP excretion was higher in both normotensive and hypertensive pregnant than in non-pregnant women (P < 0.01), whereas plasma cGMP levels were similar. A five-day nifedipine treatment (10 mg t.i.d.) had no effects on any of the variables. In hypertensive pregnancy, a reduction of systolic blood pressure by nifedipine correlated with the initial plasma atrial natriuretic peptide (P < 0.05) and a decrease in diastolic blood pressure with the initial plasma cGMP concentration (P < 0.05). The results of this small material suggest that plasma atrial natriuretic peptide concentration predicts the response to nifedipine in hypertensive pregnancy. However, the atrial natriuretic peptide-cGMP system does not seem to mediate the antihypertensive effect of nifedipine, while plasma atrial natriuretic peptide remained unaltered. Increased urinary cGMP excretion in both pregnant groups but lowered plasma atrial natriuretic peptide in normotensive pregnancy suggest other factors than circulating atrial natriuretic peptide to promote renal cGMP excretion during pregnancy.

Hypertension in pregnancy

Hypertension in pregnancy is still one of the most important causes of maternal morbidity and mortality. Several different definitions are used, partly because the pathogenetic background to the hypertensive diseases of pregnancy is not known. Widely variable incidences have been reported in different populations, but a reasonable estimation is that less than 5% of pregnancies are complicated by clinically relevant blood pressure elevation. The treatment of hypertension in pregnancy has been a matter of debate, but in late pregnancy, there is agreement that delivery is the treatment of choice. In later years, antihypertensive drugs have been less used in mild or moderate hypertension in pregnancy. Low-dose aspirin may be useful as a preventive treatment in high-risk pregnancies, but final proof of this is still lacking. Long term follow-up of women with a hypertensive pregnancy is important, since a significant proportion of these women will develop later chronic (essential) hypertension, even if their blood pressure is completely normalised shortly after delivery.

Urinary calcium/creatinine ratio in the prediction of preeclampsia

The prediction of preeclampsia by the urinary calcium/creatinine ratio during the early third trimester was assessed in 190 primigravidas, aged less than 35 years and between 28 and 32 weeks' gestation without pregnancy complications. Preeclampsia developed in 6.8% of the patients. The mean maternal age, gestational age at entry into the study and at delivery, and the average mean arterial blood pressure at entry into the study did not differ significantly between the 13 patients with subsequent preeclampsia and the 177 normotensive patients. The patients with preeclampsia did not have significantly less excretion of calcium than the normotensives.

Hypertension in pregnancy

High blood pressure, which complicates approximately 10% of all pregnancies, remains a major cause of morbidity and mortality for both mother and fetus. A relative paucity of investigative data, as well as the frequent difficulty in making an etiological diagnosis by clinical criteria alone, may be among the reasons why there are many conflicts about the management of hypertension during pregnancy. This clinical conference summarizes current concepts regarding the hypertensive disorders of gestation, focusing on the most dangerous cause, preeclampsia-eclampsia. It further highlights a recent report of the Working Group on High Blood Pressure in Pregnancy convened by the National High Blood Pressure Education Program at the National Heart, Lung, and Blood Institute (the Consensus Report). Among the Working Group's most interesting recommendations in controversial areas were a return to the classification schema suggested by the American College of Obstetricians and Gynecologists in 1972, use of the fifth Korotkoff sound to determine diastolic blood pressure levels, and institution of treatment with antihypertensive drugs for sudden elevations of blood pressure near term to diastolic levels greater than or equal to 105 mm Hg or for levels of 100 mm Hg or higher in pregnant women with chronic hypertension. The Consensus Report further recommended parenteral hydralazine and methyldopa as the drugs of choice for the acute hypertensive crisis and management of chronic hypertension, respectively, based on the long histories of safe use of these agents in gravidas. Parenteral magnesium sulfate remained the preferred therapeutic approach for avoiding or treating the convulsive complication, eclampsia, but the Working Group underscored the need for controlled trials of magnesium's efficacy. Finally, they noted that diuretics should be avoided in preeclampsia, but that these drugs can be continued during gestation if taken before conception, and may be prescribed to pregnant women with chronic hypertension who appear overly salt sensitive.

Alterations in vitamin D and calcium metabolism with magnesium sulfate treatment of preeclampsia

OBJECTIVE

Our purpose was to determine the effects of magnesium sulfate therapy on preeclamptic women and their fetuses with regard to the hormones and ions involved with calcium homeostasis, including 1,25-dihydroxyvitamin D, 25-hydroxyvitamin D, parathyroid hormone, and calcium.

STUDY DESIGN

The study group comprised 15 preeclamptic women at term treated with magnesium sulfate during labor. Controls were seven normal women in term labor. The hormones and ions were measured in maternal blood obtained at the onset of labor and at delivery and in umbilical venous (fetal) blood.

RESULTS

Baseline maternal levels of 25-hydroxyvitamin D and parathyroid hormone were lower in preeclamptics than in controls. Magnesium infusion led to significant elevations in magnesium, 1,25-dihydroxyvitamin D, 25-hydroxyvitamin D, and parathyroid hormone levels and lowered calcium concentrations. Fetuses of treated subjects demonstrated reductions in serum total and ionized calcium and elevations of 1,25-dihydroxyvitamin D and parathyroid hormone.

CONCLUSION

Magnesium sulfate infusion causes reductions in both maternal and fetal calcium levels. Both mother and fetus respond with increased 1,25-dihydroxyvitamin D and parathyroid hormone levels, which may prevent more severe maternal, fetal, and neonatal hypocalcemia.

The kidney in hypertensive pregnancies--victim and villain

Many changes in renal function occur in normal pregnancy. Without a proper understanding of these changes, routine clinical investigations may easily be misinterpreted. Women with preeclampsia have further alterations in renal function and, in occasional cases, develop acute renal failure. Understanding of abnormal renal physiology and hormonal changes in these women allows the clinician to interpret biochemical tests appropriately and make proper use of vasodilator therapy with careful attention to volume homeostasis. Women who undertake pregnancy with a primary renal disease, most commonly glomerulonephritis or reflux nephropathy, have a higher risk of adverse fetal and maternal outcomes. Awareness of these risks provides a basis for proper preconceptual counseling, as well as careful monitoring of maternal blood pressure and renal function and fetal growth during such pregnancies. These strategies will optimize the chances of a successful pregnancy outcome for both mother and baby.

Impaired 1,25-dihydroxyvitamin D production in pregnancy-induced hypertension

The aim of the study was to evaluate the calcium metabolism in pregnancy-induced hypertension. Fifty-three women with pregnancy-induced hypertension were studied and the control groups comprised 20 women with uncomplicated pregnancies in the third trimester and 51 non-pregnant women, respectively. The mean serum concentrations of 1,25-dihydroxyvitamin D in women with pregnancy-induced hypertension was low (38.6 +/- 21.4 pg/ml) compared to women with uncomplicated pregnancies (91.0 +/- 18.2 pg/ml), but comparable to levels in non-pregnant women (32.2 +/- 11.9 pg/ml). Mean serum levels of PTH and ionized calcium were comparable in women with pregnancy-induced hypertension and women with uncomplicated pregnancies. In conclusion, the calcium metabolism in pregnancy-induced hypertension was changed compared to uncomplicated pregnancies with respect to the serum concentration of 1,25-dihydroxyvitamin D.

Calcium supplementation prevents hypertensive disorders of pregnancy

Preeclampsia, a hypertensive disorder of pregnancy, is a major cause of fetal and maternal morbidity and mortality. Epidemiologic studies have shown an inverse relationship between dietary calcium intake and gestational hypertension. A recent large-scale, randomized, double-blind, placebo-controlled clinical trial has shown that supplementation of pregnant women with 2 g calcium per day from the twentieth week of gestation to term can significantly lower the incidence of hypertensive disorders of pregnancy. The beneficial effect of calcium supplementation was apparent as early as the twenty-eighth week of gestation. The mechanism responsible for the effects of calcium on gestational hypertension is unknown.

Abnormal 1,25-dihydroxyvitamin D metabolism in preeclampsia

We previously reported that preeclampsia is associated with hypocalciuria (N Engl J Med 1987; 316:715). The purpose of this study was to determine whether alterations in calcium regulatory hormones are present in preeclampsia and, if so, whether they are responsible for hypocalciuria. Thirty-two pregnant women were studied in the second and third trimesters of pregnancy (11 women with preeclampsia, nine with chronic hypertension, and 12 normotensive women). 1,25-Dihydroxyvitamin D, C-terminal parathyroid hormone, ionized calcium, and urinary calcium excretion were measured. 1,25-Dihydroxyvitamin D was significantly lower in the women with preeclampsia in the third trimester when the disease developed (37.8 +/- 15 pg/ml) than in women with chronic hypertension (75 +/- 15 pg/ml, p less than 0.05) and normal women (65 +/- 10 pg/ml, p less than 0.05). Parathyroid hormone was higher, but not significantly, in those with preeclampsia. Ionized calcium was not significantly different among the three groups. Urinary calcium excretion was abnormally low for pregnancy (less than 50 mg/24 hr) in all but one women with preeclampsia. We conclude that 1,25-dihydroxyvitamin D is reduced in preeclampsia and may lead to hypocalciuria by causing decreased intestinal absorption of calcium, stimulation of parathyroid hormone, and increased distal renal tubular resorption of calcium. The cause of reduced 1,25-dihydroxyvitamin D in preeclampsia is unknown and may be due to either diminished renal or placental production of the hormone.

The effect of pregnancy on renal function: physiology and pathophysiology

Marked changes in renal function occur with pregnancy. We present a summary of these changes in this review and give insight into possible mechanisms if they are known. Controversies exist regarding the therapy of pregnancy-induced hypertension and asymptomatic and recurrent bacteriuria. The current views on these topics are given. Specific renal diseases are summarized, including transplantation, and optimum management strategies and maternal and fetal prognosis during pregnancy are given.

Calcium supplementation to prevent hypertensive disorders of pregnancy

BACKGROUND

Calcium supplementation has been reported to reduce blood pressure in pregnant and nonpregnant women. We undertook this prospective study to determine the effect of calcium supplementation on the incidence of hypertensive disorders of pregnancy (gestational hypertension and preeclampsia) and to determine the value of urinary calcium levels as a predictor of the response.

METHODS

We studied 1194 nulliparous women who were in the 20th week of gestation at the beginning of the study. The women were randomly assigned to receive 2 g per day of elemental calcium in the form of calcium carbonate (593 women) or placebo (601 women). Urinary excretion of calcium and creatinine was measured before calcium supplementation was begun. The women were followed to the end of their pregnancies, and the incidence of hypertensive disorders of pregnancy was determined.

RESULTS

The rates of hypertensive disorders of pregnancy were lower in the calcium group than in the placebo group (9.8 percent vs. 14.8 percent; odds ratio, 0.63; 95 percent confidence interval, 0.44 to 0.90). The risk of these disorders was lower at all times during gestation, particularly after the 28th week of gestation (P = 0.01 by life-table analysis), in the calcium group than in the placebo group, and the risk of both gestational hypertension and preeclampsia was also lower in the calcium group. Among the women who had low ratios of urinary calcium to urinary creatinine (less than or equal to 0.62 mmol per millimole) during the 20th week of gestation, those in the calcium group had a lower risk of hypertensive disorders of pregnancy (odds ratio, 0.56; 95 percent confidence interval, 0.29 to 1.09) and less of an increase in diastolic and systolic blood pressure than the placebo group. The pattern of response was similar among the women who had a high ratio of urinary calcium to urinary creatinine during the 20th week of gestation, but the differences were smaller.

CONCLUSIONS

Pregnant women who receive calcium supplementation after the 20th week of pregnancy have a reduced risk of hypertensive disorders of pregnancy.

Prevention and treatment of pregnancy-associated hypertension: what have we learned in the last 10 years?

High blood pressure (BP) complicates approximately 10% of all pregnancies. Hypertension in pregnancy falls into four categories: (1) preeclampsia-eclampsia, (2) chronic hypertension of whatever cause, (3) preeclampsia-eclampsia superimposed to chronic hypertension or renal disease, and (4) transient or late hypertension (gestational hypertension). Preeclampsia, the association of hypertension, proteinuria, and edema, accounts for more than 50% of all the hypertensive disorders of pregnancy and is a major cause of fetal and maternal morbidity and mortality. Unfortunately, distinguishing between preeclampsia and other causes of hypertension on clinical grounds can be difficult because of the lack of specific tests for differential diagnosis. Increased vascular resistance has been claimed as the primary cause of preeclampsia; however, a variable hemodynamic profile with relatively high cardiac outputs, normal filling pressures, and inappropriately high systemic vascular resistances is now reported by most investigators. Imbalance between vasodilator and vasoconstrictor eicosanoids may account for platelet activation and increased responsiveness to pressor peptides. Altered prostacyclin (PGI2) to thromboxane A2 (TxA2) ratio in maternal uteroplacental vascular bed may favor local platelet activation and vasoconstriction contributing to placental insufficiency and fetal distress. Alternatively, recent evidence seems to suggest that fetal umbilical placental circulation may be the site of the primary vascular injury. Whether low-dose aspirin prevents preeclampsia because it inhibits the excessive maternal TxA2 or whether the partial inhibition of fetal TxA2 is also of therapeutic value remains to be established. Treatment of severe hypertension in pregnancy is probably important to prevent cardiac failure or cerebrovascular accidents in the mother. The need for pharmacological therapy of mild to moderate hypertension is still debated, since no formal studies are available to clarify whether pharmacological treatment in such instances effectively reduces maternal or fetal risk. For the treatment of preeclampsia, hydralazine and nifedipine may be used when delivery is not applicable. Labetalol and diazoxide are effective for hypertensive emergencies. Life-threatening hypertension that does not respond to more conventional therapy is an indication for the use of sodium nitroprusside. For chronic hypertension, alpha-methyldopa remains the treatment of choice; if ineffective, hydralazine or beta-blockers are suitable. Effectiveness and safety of other molecules remain elusive.

Early detection of preeclampsia

The signs and symptoms of preeclampsia are usually apparent at a relatively late stage in pregnancy (late second to early third trimester). However, the disorder results from abnormal interaction between fetal and maternal tissue much earlier in pregnancy, between 8 and 18 weeks' gestation. During the past two decades numerous clinical, biophysical, and biochemical tests have been proposed for the early detection of preeclampsia. Some of these tests are simple, whereas others are invasive; some have been studied extensively, while others are still under clinical investigation. A review of the literature indicates considerable disagreement regarding the sensitivity and predictive values of the various tests studied. The reported differences in the predictive values of these tests may be attributed to one or more of the following: populations studied, definition and prevalence of the disorder, techniques and methodology used in performing these tests, etc. As a result, there is disagreement regarding the ideal screening test to be used for identifying patients for clinical trials dealing with prevention of the disorder.

Plasma concentrations of atrial natriuretic factor and hemodynamics in pregnancy-induced hypertension

Plasma values of atrial natriuretic factor (ANF) were evaluated in 31 women with pregnancy-induced hypertension (PIH) and 31 normal pregnant women at the same age of gestation. In 27 women with PIH and 27 normal pregnant women forearm venous tone (FVT) was evaluated by Strain Gauge Plethysmography. Forearm vascular resistance (FVR) was measured as the ratio of mean blood pressure (MBP) to forearm blood flow. In addition Cardiac Index (CI) by means of transthoracic electrical bioimpedance and total peripheral vascular resistance (TPR) (with the Frank Equation) were also measured. In comparison with the normal pregnant women, the women with PIH had similar values of hematocrit (as an index of plasma volume) and significantly higher levels of FVR and TPR, while ANF plasma values did not differ significantly. Subdividing the women with PIH in relation to the presence of proteinuria (greater than or equal to 0.3 g/l), those with proteinuria, in addition to significantly higher levels of FVR and TPR, had significantly higher levels of FVT than normal pregnant women, while ANF plasma values were higher even though the difference was only near the level of significance. Hypertensive women with proteinuria also had higher values of FVT than hypertensive women without proteinuria. By means of multiple regression ANF did not show any significant correlations with hematocrit or sodium excretion. Hypertension with proteinuria seems to represent a more severe form of the disease in which, in addition to the probable influence of other factors such as the renin-angiotensin and prostaglandin systems, a greater increase in peripheral sympathetic tone than in hypertension alone appears to be present, causing a reduction in venous compliance in addition to the elevation in FVR and TPR, with increase in central blood volume and atrial stretch. This may explain the higher ANF plasma levels in these patients in comparison with normal pregnant women, even though the absence of a significant correlation of ANF with hematocrit and the fact that ANF increase was only near the level of significance may suggest a change in the relation between ANF secretion and atrial volume receptors in pregnancy either normal or complicated by hypertension. ANF does not seem to play an important role in water and sodium excretion in PIH probably because of the presence of very high plasma levels of hormones such as aldosterone, progesterone and oestriol which, together with renal prostaglandins, seem to be involved in diuresis and natriuresis in pregnancy.

National High Blood Pressure Education Program Working Group Report on High Blood Pressure in Pregnancy

This consensus report focuses the presentation, pathophysiology, and management of the hypertensive disorders of pregnancy expanding on recommendations first presented in 1988 by the Joint National Committee on Detection, Evaluation, and Treatment of High Blood Pressure. Practicing physicians should determine whether a patient's hypertension during pregnancy falls into the classification of (1) chronic hypertension, (2) preeclampsia, (3) preeclampsia superimposed on chronic hypertension, or (4) transient hypertension. The distinction, for management considerations, is made between hypertension that is present before pregnancy (chronic and preexisting) and that occurring as part of the pregnancy-specific condition preeclampsia. When maternal blood pressure reaches diastolic levels of 100 mm Hg or greater, treatment should be instituted to avoid hypertensive vascular damage. The report includes a discussion of antihypertensive therapy specific to the chronic or acute hypertension occurring concomitantly with pregnancy. The roles of calcium supplementation and low-dose aspirin to prevent preeclampsia and chronic and transient hypertension are under investigation.

Hypocalciuria in hypertensive disorder in pregnancy and how to measure it

We studied the urinary calcium excretion in 41 patients in the third trimester of pregnancy. There was a significant decrease in 24-hour calcium excretion in hypertensive and pre-eclamptic patients. The 24-hour calcium excretion correlated well with the calcium to creatinine ratio of a single voided urine sample. We conclude that measuring urinary calcium excretion may be valuable in the care and the study of pregnant patients with hypertensive disorders, and that the 24-hour urinary calcium excretion can be estimated from a single voided urine sample.

Dietary calcium and chronic diseases

The Agricultural Revolution was almost certainly associated with a substantial decrease in human calcium intake. Calcium intakes typical of contemporary humans may well be inadequate for many individuals. Various slowly developing chronic disorders such as osteoporosis, hypertension, hyperlipidemia, and colon cancer may be induced or exaggerated by the current low level of dietary calcium intake in Western societies. We propose two hypotheses relating calcium intake to diverse diseases: first, the adaptation required to adjust to low intakes is inadequate to maintain critical components of cellular calcium regulation; second, the constant, forced adaptive response to low intake itself produces untoward consequences.