|Year : 2013 | Volume
| Issue : 1 | Page : 1-5
Serum sodium, potassium, calcium and magnesium in women with pregnancy induced hypertension and preeclampsia in Oredo local Government, Benin Metropolis: A pilot study
Olanike Funmilola Adewolu
Department of Chemical Pathology, University of Benin, Benin City, Edo State, Nigeria
|Date of Web Publication||19-Apr-2014|
Olanike Funmilola Adewolu
Department of Chemical Pathology, University of Benin, Benin City, Edo State
Source of Support: None, Conflict of Interest: None
Background: Pregnancy induced hypertension and preeclampsia (hypertension in pregnancy in association with the excretion of >300 mg of urinary protein per day after 20 weeks of gestation) is one of the most common complications of pregnancy seen in Benin City, Nigeria. It contributes significantly to maternal mortality, premature birth, intrauterine growth retardation and perinatal mortality. Studies have been performed to evaluate the role of electrolytes in etiopathogenesis of pregnancy induced hypertension and preeclampsia. The outcome of the studies has varied ina different environment and population. Objective: The objectiveof this study is to determine the role of serum sodium, potassium, magnesium and calcium in etiopathogenesis of preeclampsia in this environment. Materials and Methods: A total of 60 subjects were involved in the study. 20 were normotensive non-pregnant women, 20 normotensive pregnant women, 20 with preeclampsia. They were of similar age groups, with singleton pregnancies and in the second and third trimester of pregnancy. Serum sodium, potassium, calcium, magnesium was assayed in the three groups. Serum sodium and potassium was assayed using the ion-selective electrode method. Statistical analysis was done using SPSS Student Version 13 for Windows. Results: Mean serum sodium was non-significantly raised in women with preeclampsia above the upper limit of normal reference interval (151 ± 1.5 mmol/l) (P > 0.05) while it was within normal reference interval of 140 ± 2.3 mmol/L for normotensive pregnant women and 144 ± 4.2 mmol/L for normotensive non-pregnant women. Serum potassium, calcium, magnesium were all within normal reference intervals across the three groups studied. Conclusion: Serum sodium, potassium, calcium, magnesium do not seem to play a vital role in the etiopathogenesis of preeclampsia in this environment as there was no statistically significant difference in the values of the electrolytes assayed across the three groups studied.
Keywords: Electrolytes, preeclampsia, pregnancy induced hypertension
|How to cite this article:|
Adewolu OF. Serum sodium, potassium, calcium and magnesium in women with pregnancy induced hypertension and preeclampsia in Oredo local Government, Benin Metropolis: A pilot study. Afr J Med Health Sci 2013;12:1-5
|How to cite this URL:|
Adewolu OF. Serum sodium, potassium, calcium and magnesium in women with pregnancy induced hypertension and preeclampsia in Oredo local Government, Benin Metropolis: A pilot study. Afr J Med Health Sci [serial online] 2013 [cited 2019 Jul 22];12:1-5. Available from: http://www.ajmhs.org/text.asp?2013/12/1/1/129914
| Introduction|| |
Preeclampsia is a transient but potentially dangerous complication of pregnancy that affects 3-5% of pregnancies. , It has been termed the "disease of theories" because of the multiple hypotheses that have been proposed to explain its occurrence. 
The etiology of preeclampsia is yet to be fully elucidated despite numerous studies that have been done. Some studies have concluded that changes in levels of blood metals observed in preeclamptic patients, may implicate the pathogenesis of preeclampsia. , Other studies have however not shown an association between the serum concentration of these elements and occurrence of preeclampsia. ,
The high rate of preeclampsia in developing countries have made some authors come to the conclusion that malnutrition is a risk factor in the etiology of preeclampsia, in some cases deficit intake of calcium and zinc has been implicated.  Although some studies have claimed that calcium and magnesium have a relevant effect on the blood vessels of pregnant women,  other studies have revealed that serum sodium and potassium levels vary in women with pregnancy induced hypertension compared with normotensive pregnant women.  However, all these appear to be risk factors or predisposing factors to preeclampsia. No general consensus seems to have been reached yet on the role electrolytes play in the etiopathogenesis of preeclampsia. This study was carried out to find out the role sodium, potassium, calcium and magnesium may play in the etiopathogenesis of preeclampsia in this environment.
| Materials and Methods|| |
This was a cross-sectional study carried out in the State Specialist Hospital in Benin City, Edo state between August 2010 and May 2011. The study included 20 normotensive non-pregnant women (who served as controls), 20 normotensive pregnant women who were attending antenatal clinic in the out-patients department of the hospital and 20 women with preeclampsia, some who were on admission in the ward while some were attendees in the antenatal clinic in the hospital. They were all within the same age range. All the pregnant women had singleton pregnancies and in their second and third trimester of pregnancy. They all had gestational ages greater than 20 weeks. Approval for the study protocol was granted by the Ethical committee of the State Specialist Hospital, Benin City, Edo State. Informed consent was obtained from the subjects and controls before the collection of blood samples.
All cases were selected by taking a detailed medical history. Structured questionnaire was used to obtain information about age, gestational age, previous obstetric history and previous history of hypertension, history of diabetes or kidney diseases. Those with preeclampsia were selected based on the following:
- New onset of hypertension after 20 weeks of gestation with blood pressure ≥140/90 mmHg or rise in blood pressure of systolic >30 mmHg and diastolic >15 mmHg above booking blood pressure; in at least two occasions.
- Proteinuria >300 mg per day detected by dipsticks.
- Any other systemic disease.
The normotensive pregnant women were selected after meeting the inclusion criteria below.
- Blood pressure <140/90 mmHg and no rise in blood pressure in pregnancy up to 30 mmHg systolic and 15 mmHg diastolic above booking blood pressure.
- No proteinuria.
The non-gravid subjects were not hypertensive, nor diabetic, nor had any history of kidney disease.
General physical examination was carried out for all patients. Blood pressure was measured, with patients in a comfortable restful position using a sphygmomanometer on at least two occasions.
A total volume of seven millilitre of venous blood was collected from the antecubital vein without stasis and dispensed into two separate sample bottles. A total of three millilitre was dispensed into lithium heparin bottle for sodium and potassium assay, while four millilitre was dispensed into a plain sample bottle for calcium and magnesium assay. Blood in the plain bottle was allowed to clot and then centrifuged at 300 rpm for five minutes and the serum aspirated and dispensed into plain tubes and stored at −20°C until the time of analysis.
Blood in the lithium heparin bottle was also centrifuged at 3000 rpm and plasma aspirated and dispensed into plain tubes and stored at −20°C until the time for analysis.
Plasma sodium and potassium were measured using the ion-selective-electrode method. Serum magnesium was assayed by the calmagite dye method and calcium by o-cresolphtalein complex one method. Three levels of control sera were run with every batch of the assays to ensure accuracy and quality assurance.
Statistical analysis was performed using SPSS version 13. Differences between means were analyzed using the Student's T-test. Pearsons correlation was used to analyze the correlation between variables. ANOVA was used to determine significant differences between groups. Level of significance P value was taken at P < 0.05.
| Results|| |
The study population was 60. Mean ages of the three groups were 30 years, 29.2 ± 4.1 years, 30.1 ± 3.5 years for the normotensive non pregnant, normotensive pregnant and women with preeclampsia respectively [Table 1]. Mean gestational ages was 25.5 ± 7 and 32.7 ± 5.8 weeks for the normotensive pregnant women and women with preeclampsia respectively.
Mean serum sodium was 144 ± 4.2 mmol/L, 140 ± 2.3 mmol/L, 151 ± 1.5 mmol/L (P = 0.259) for normotensive non-pregnant, normotensive pregnant and women with preeclampsia respectively [Table 2].
|Table 2: Serum concentration of the electrolytes in the normotensive, non-pregnant, normotensive pregnant and preeclamptic women |
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Mean plasma potassium was 4.2 ± 1.2 mmol/L, 4.2 ± 0.3 mmol/L, 4.3 ± 0.7 mmol/L (P = 0.803) for normotensive non-pregnant, normotensive pregnant and women with preeclampsia [Table 2].
Mean serum calcium was 2.33 ± 0.3 mmol/L, 2.12 ± 0.3 mmol/L, 2.18 ± 0.2 mmol/L (P = 0.257) for normotensive non-pregnant, normotensive pregnant and women with preeclampsia respectively [Table 2].
Mean serum magnesium was 0.95 ± 0.2 mmol/L, 0.85 ± 0.2 mmol/L, 1.02 ± 0.4 mmol/L (P = 0.478) for the normotensive non-pregnant and normotensive pregnant and women with preeclampsia respectively [Table 2].
There was a non-significant positive correlation between gestational age and systolic blood pressure (r = 0.472) (P = 0.088) and diastolic blood pressure (r = 0.403) (P = 0.172). This was not statistically significant.
Sodium also showed a non-significant positive correlation with systolic blood pressure (r = 0.391) (P = 0.149) and diastolic blood pressure (r = 0.272) (P = 0.347).
| Discussion|| |
The estimation of serum electrolytes in pregnancy induced hypertension provides a very useful index for the study of physiological and pathological changes during pregnancy. 
Primary hypertension results from the interplay of internal derangements (primarily in the kidney) and the external environment.  Numerous studies show an adverse effect of serum sodium on arterial pressure. ,,, Some studies in Nigeria have also revealed similar findings. ,
In the present study, mean serum sodium was above the normal reference interval in women with preeclampsia while it was within the normal reference interval for normotensive pregnant and normotensive non-pregnant women. This difference was however not statistically significant. Although some studies have demonstrated statistically significant raised serum sodium levels in women with preeclampsia, some other studies have reported normal serum sodium levels.  The observations have varied with different populations. The role of sodium in etiopathogenesis of preeclampsia therefore remains equivocal. The mild hypernatraemia observed in the preeclamptic women in this study may be an indication of likely role sodium may play in the etiopathogenesis of preeclampsia in this environment. Studies by Ejike and Ugwu  in a population of non-urban dwelling Nigerians reported a significant correlation between urinary sodium (which is a measure of sodium intake) and diastolic blood pressure. Azinge et al. also reported that urinary sodium, which was a measure of sodium intake, is increased in subjects with hypertension in Nigeria. Tayo et al. reported sodium and potassium to be strongly correlated with blood pressure in Africans in the diaspora in the United States, this included Nigerians, Jamaicans and Afro-Americans. These studies tend to point to an association between sodium and blood pressure in this environment. In the present study, sodium showed a positive correlation with systolic and diastolic pressure, though this was not statistically significant. Therefore, while it cannot be conclusively said that raised sodium levels has a definite role to play in the etiopathogenesis of preeclampsia, the findings maybe suggestive of a possible role, maybe as a predisposing factor or as a risk factor in already predisposed individuals. This still needs to prove as this study did not establish that, these are still areas for further research studies. A longitudinal type of study may be beneficial.
Mean serum potassium was within normal reference interval across the three groups studied, there was no statistically significant difference. Bera et al. made a similar observation in an Indian population while Yussif et al. reported a significant difference in serum potassium level between hypertensive pregnant women and normotensive pregnant women in an Iraqi population. In their study, serum potassium was lower in hypertensive pregnant than in the normotensive pregnant women. Their hypotheses were that raised sodium level and low potassium level in hypertensive pregnant women could be a causative agent of gestational hypertension. Some clinical studies have shown that a diet low in potassium (10-16 mmol/day) coupled with the participant's usual sodium intake (120-200 mmol/day) caused sodium retention and elevation of blood pressure.  While sodium levels was non-significantly raised in preeclamptic patients in this study, serum potassium was within normal reference interval; therefore, the electrolyte picture in preeclampsia may vary in different population and environment.
Mean plasma calcium was within normal reference interval across the three groups with no statistically significant difference. The same findings was reported by Golmohammad et al.,  there was no significant difference in serum calcium between patients with preeclampsia and normotensive controls in their studies. Indumati et al.  and Mohieldein et al. however reported a significant decrease in serum total and ionized calcium in patients with pregnancy induced hypertension, compared with normotensive controls in their own studies. Dietary calcium deficiency has been proposed as a possible cause of preeclampsia by some authors, but Levine et al. in a prospective study in an American population showed that calcium supplementation during pregnancy did not prevent preeclampsia in healthy nulliparous women. Conversely, Crowther et al.  in Australia and Herrera et al.  in Colombia reported in their own studies lowering of blood pressure with calcium supplementation in primigravid women, therefore role of calcium deficiency in etiopathogenesis of preeclampsia is yet to be universally proven.
Serum magnesium was within normal reference interval for the three groups studied, with no statistically significant difference. Golmohammad et al. made the some observation in an Indian population. However, Igberase et al.  reported a significantly lower serum magnesium level in preeclamptic gestation compared with the normotensive pregnant women and therefore proposed hypomagnesaemia as a possible predictor of preeclampsia. Some authors such as Standley et al. in Michigan, USA and Indumati et al.  in India have also reported a significant decrease in serum magnesium in women with preeclampsia in their studies and proposed hypomagnesaemia as a possible cause of preeclampsia. Magnesium affects the cardiac and smooth muscle cells by altering the transfer of calcium and its binding to the membrane and organ cells. Magnesium acts peripherally to produce peripheral vasodilatation and a fall in blood pressure. Thus, low levels of magnesium predispose to an increase in arterial pressure. Magnesium sulfate is used for the treatment of seizure and prophylaxis in women with preeclampsia and eclampsia.  Just as have been observed with calcium, it is yet to be proven universally that hypomagnesaemia plays a prominent role in the pathogenesis of preeclampsia.
Etiopathogenesis of preeclampsia still appears to be multifactorial, with some known risk factors. The role and impact of dietary deficiencies of calcium, magnesium in etiopathogenesis of pregnancy induced hypertension and preeclampsia remains equivocal, a universal observation is yet to be reported. The role sodium and potassium also play may be contributory, especially in already predisposed individuals, rather than major causative factors. Further studies still need to be carried out.
| Conclusion|| |
Serum sodium, potassium, calcium and magnesium do not seem to play a significant or dominant role in the etiopathogenesis of preeclampsia in this environment. In individuals who are already predisposed to this condition, their roles may not be ruled out completely. Other factors not highlighted in this study, may play more important roles in the etiopathogenesis of preeclampsia.
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[Table 1], [Table 2]