Comparative Study of Plasma Electrolyte Status in Pre-eclamptic and Normotensive Pregnant Women in Zaria

Abstract

Background:

Pre-eclampsia is a major cause of maternal and perinatal morbidity, characterized by endothelial dysfunction and renal impairment that may alter electrolyte balance. However, findings on electrolyte disturbances remain inconsistent, and the absence of population-specific reference intervals limits clinical interpretation in low-resource settings.

Objective:

To evaluate plasma electrolyte patterns among pre-eclamptic and normotensive pregnant women and establish locally relevant reference intervals for electrolyte parameters in Zaria, Nigeria.

Methods:

A comparative cross-sectional study was conducted at Ahmadu Bello University Teaching Hospital, Zaria, from January to August 2024. A total of 222 pregnant women were enrolled, comprising 100 women with pre-eclampsia and 122 normotensive controls. Plasma sodium, potassium, chloride, and bicarbonate concentrations were measured using an ion-selective electrode analyzer. Independent t-tests and chi-square tests were used for group comparisons, while multivariable linear and logistic regression analyses adjusted for gestational age. Reference intervals were derived from the normotensive cohort.

Results:

Mean concentrations of sodium, potassium, chloride, and bicarbonate did not differ significantly between groups (all p > 0.05). However, hyponatraemia was significantly more prevalent among women with pre-eclampsia than controls (44.0% vs. 27.9%) and remained independently associated with pre-eclampsia after adjustment for gestational age (adjusted OR 3.54, 95% CI 1.75–7.17; p < 0.001). No significant differences were observed in potassium, chloride, or bicarbonate abnormalities. Reduced bicarbonate levels in both groups were consistent with physiological renal compensation for pregnancy-related respiratory alkalosis. Locally derived reference intervals showed modest differences from conventional ranges.

Conclusion:

Electrolyte disturbances in pre-eclampsia are better reflected by distributional abnormalities than by differences in mean concentrations. The strong association between hyponatraemia and pre-eclampsia highlights its potential clinical relevance and underscores the need for context-specific reference intervals and prospective studies to determine its temporal and prognostic significance.

Introduction

Pre-eclampsia, defined by new-onset hypertension after 20 weeks’ gestation with proteinuria or end-organ impairment, is a leading cause of maternal and perinatal morbidity and mortality.¹ Its pathophysiology is rooted in abnormal placentation, systemic endothelial dysfunction, glomerular injury, inflammatory activation, and altered vascular permeability, all of which disturb fluid and electrolyte balance. Derangements in sodium, potassium, chloride, and bicarbonate may indicate disrupted renal handling, neurohormonal dysregulation, particularly renin–angiotensin–aldosterone system (RAAS) pathways, and intravascular–interstitial volume shifts. However, evidence regarding these electrolyte patterns remains inconsistent and context-specific, highlighting the importance of characterizing them in local populations such as Zaria, Nigeria.

Several recent case–control and cross-sectional studies have observed that pre-eclamptic women tend to present with significant electrolyte alterations compared to normotensive pregnant women.^2,3 Some studies report a tendency toward lower serum sodium and potassium in pre-eclampsia.² Others describe the opposite pattern, higher sodium with lower potassium,³ or only modest differences in chloride or bicarbonate levels.⁴ Mechanistic research supports these observations, showing that erythrocyte Na⁺/K⁺-ATPase activity, which normally increases during uncomplicated pregnancy, is significantly reduced in more severe cases of pre-eclampsia, indicating disrupted cellular electrolyte transport.⁵ Clinically, hyponatraemia in pre-eclamptic women has been associated with more severe disease manifestations, including acute kidney injury, fetal growth restriction, HELLP syndrome, and increased likelihood of ICU admission, particularly when sodium falls below a critical threshold.⁶

The observed electrolyte disturbances in pre-eclampsia likely arise from a confluence of mechanisms. Endothelial activation and capillary leakage can lead to intravascular volume depletion or dilutional states. Impaired renal perfusion and glomerular endothelial dysfunction alter tubular solute handling. Dysregulation of neurohormonal systems, most notably the RAAS, can affect sodium retention and potassium excretion. Independent studies have also linked high salt intake with increased risk of pre-eclampsia, although direct correlations with aldosterone levels remain inconclusive.⁷ At the cellular level, reduced Na⁺/K⁺-ATPase activity in erythrocytes reflects systemic dysregulation in electrolyte transport.⁵ Collectively, these pathways predispose to diverse patterns of sodium and potassium derangements, which may significantly influence volume status, blood pressure control, and associated maternal-fetal complications.⁷

In contrast, an uncomplicated pregnancy is characterized by finely tuned adaptations that preserve electrolyte equilibrium. Plasma volume expands significantly, renal blood flow and glomerular filtration rate increase, and progesterone-driven hyperventilation induces a mild respiratory alkalosis with compensatory renal bicarbonate excretion.⁹ Renal tubular changes are key: epithelial sodium channels (ENaC) are upregulated to enhance sodium reabsorption; potassium-retaining transporters such as the HKA2 are augmented; and potassium-secretory channels such as ROMK and BK are downregulated, promoting potassium conservation.⁹ Throughout gestation, plasma sodium and potassium levels follow predictable patterns, initially decreasing and then rising toward term, while chloride and osmolality display dynamic fluctuations.¹⁰ These physiologic adjustments shift “normal” reference ranges and highlight the importance of gestational age in interpreting serum electrolyte values.

Because pre-eclampsia disrupts these meticulously regulated adaptations, electrolyte deviations may carry critical diagnostic, prognostic, and therapeutic implications. Hyponatraemia may signal worsening disease or impending complications, while hypokalaemia can magnify vascular instability or arrhythmic risk.^2,3,,6 Conversely, volume overload states with hypernatraemia may complicate fluid management decisions.³ Without region-specific reference intervals in pregnancy, clinicians may misinterpret laboratory findings.

In Zaria, where dietary practices, environmental exposures, and healthcare dynamics differ, it is particularly important to establish normative electrolyte profiles in uncomplicated pregnancy and then delineate how these diverge in pre-eclamptic women across disease severities.

To address this gap, our study employs a combined case–control and cross-sectional design in Zaria to compare serum sodium, potassium, chloride, and bicarbonate levels between pre-eclamptic women and matched normotensive pregnant controls. We characterized the prevalence, direction, and magnitude of electrolyte abnormalities as well as established the reference ranges for these electrolytes in Zaria. These insights may inform critical management decisions, including fluid therapy, antihypertensive regimens, and anticonvulsant dosing, and contribute valuable contextual data to the broader understanding of electrolyte dynamics in pre-eclampsia, especially in sub-Saharan African settings.

Materials and Methods

The study was a comparative cross-sectional study with derivation of reference intervals for plasma electrolytes in normotensive pregnant women. It combined a case-control comparison between pre-eclamptic and normotensive groups with the establishment of local reference ranges using the normotensive cohort. It was carried out at Ahmadu Bello University Teaching Hospital, Zaria, Kaduna State, Nigeria, between January and August, 2024. Using a power-based formula for continuous variables (90% power, 5% significance, SD = 0.36, mean difference = 0.18, and a 10% non-response adjustment), the minimum sample size was calculated as 100 pre-eclamptic participants and 122 normotensive pregnant participants to calculate the reference range. Pre-eclampsia was defined as the presence of proteinuria with blood pressure of ≥140 mmHg systolic and ≥ 90 mmHg diastolic at gestational age ≥20 weeks.¹¹ Participants were between 18 and 40 years old, not on any medication aside from routine iron and folic acid, and had no history of chronic diseases. Normotensive participants were recruited consecutively from the antenatal clinic, while pre-eclamptics were recruited from both the antenatal clinic and labour ward of the Obstetrics and Gynaecology Department of ABUTH.

After obtaining informed consent, participants’ demographic and clinical data, including age, occupation, level of education, parity, and gestational age, were recorded using a structured data collection form. Blood pressure was measured using a sphygmomanometer (Accuson, Italy) and a stethoscope. Measurements were taken on the right arm with the participant in a seated position. Two readings were obtained at 15-minute intervals, and the average value was recorded.

The study was approved by the Ahmadu Bello University Teaching Hospital Health Research Ethics Committee (approval number: ABUTH/HREC/F43/2023, dated 14^th August, 2023)

Analysis was performed at the participants' bedside using the EDAN i15VET Blood Gas and Electrolyte Analyser. The EDAN i15VET analyser utilises ion-selective electrode analysis to measure electrolytes. The machine was switched on, calibrated, and ready to receive samples. Then, a 3 mL venous blood sample was collected from the antecubital vein using a sterile 21-gauge hypodermic needle attached to a 5 mL heparinized syringe, following disinfection of the puncture site with methylated spirit under aseptic conditions. The syringe was attached to the cartridge and subsequently inserted into the machine. Results were generated and documented in the data collection forms. The EDAN i15VET analyser was calibrated daily, and quality control was performed twice using manufacturer-provided control materials (levels 1 and 2) throughout the study period. No significant drift was observed.

Data obtained from the study were analysed using Statistical Package for the Social Sciences 25.0 (SPSS 25.0) for Windows (SPSS Inc., Chicago, IL, USA) and Microsoft Excel 2016. Qualitative values were summarised as percentages, frequencies, and tables. The distributions of quantitative variables were assessed using the Kolmogorov-Smirnov test. The concentrations of electrolytes were compared using a t-test, while correlations were done using Pearson’s test. Multivariable linear and logistic regression analyses were applied to adjust for gestational age. Reference intervals were established according to CLSI EP28-A3c guidelines using the normotensive cohort.¹² The level of statistical significance was set at a p-value of ≤ 0.05.

Result

The mean age was similar between normotensive (29.10 ± 5.82 years) and preeclamptic participants (28.2 ± 5.4 years) (p = 0.878). A higher proportion of normotensive participants had tertiary education (82.6%) compared to preeclamptic participants (58%), while housewives were more represented among preeclamptic participants (46%) and civil servants among normotensive women (31.1%). Estimated gestational age was higher in preeclamptic participants (35.74 ± 4.36 weeks) than in normotensive participants (30.24 ± 4.60 weeks) (p < 0.001). Because gestational age differed significantly between groups (p < 0.001), all comparisons were adjusted for. Systolic and diastolic blood pressures were higher in preeclamptic participants (164.40 ± 19.57 mmHg and 108.33 ± 14.56 mmHg) compared to normotensive participants (104.25 ± 12.7 mmHg and 67.89 ± 8.3 mmHg), respectively (p < 0.001), while median parity was 2.45 and 3.44, respectively. -Table I.

Table I:

Clinico-Socio-demographic characteristics of the study participants

Variable	Normotensive pregnant participants (n=122)	Preeclamptic participants (n= 100)	p-value
Age (Mean ± SD)	29.10 ± 5.82	28.2 ± 5.4	0.878
Level of Education
None	2 (1.6%)	6 (6%)
Primary	8 (4.9%)	10 (10%)
Secondary	22 (18.0%)	26 (26%)
Tertiary	92 (82.6%)	58 (58%)
Occupation
Artisan	5 (4.1%)	6 (6%)
Business	18(14.8%)	16 (16%)
Civil servant	38 (31.1%)	13 (13%)
House wife	37 (30.3%)	46 (46%)
Student	24(19.7%)	19(19%)
EGA (weeks)	30.24±4.60	35.74 ± 4.36	<0.001
Blood pressure (Mean ± SD)
Systolic BP (mmHg)	104.25±12.7	164.40 ± 19.57	<0.001
Diastolic (mmHg)	67.89±8.3	108.33 ± 14.56	<0.001
*Parity	2.45 (3.7)	3.44 (4.0)

* Median (IQR) was used as the data is not normally distributed

SD: Standard Deviation, n: number of participants

mmHg: Millimeter of Mercury

IQR: Interquartile Range

In the unadjusted analysis, mean plasma electrolyte concentration levels were similar between normotensive participants (Na⁺: 136.93 ± 3.02, K⁺: 3.61 ± 0.32, Cl^-:108.75 ± 2.48, and HCO³: 21.56 ± 2.17 mmol/L) and preeclamptic participants (Na⁺: 136.34 ± 6.55, K⁺: 3.58 ± 0.56, 107.26 ± 16.36, and HCO³: 20.79 ± 4.87 mmol/L), (p > 0.05 for all). After adjusting for gestational age using multiple linear regression, the differences remained statistically nonsignificant. The adjusted mean differences (pre-eclamptic minus normotensive) were: sodium −0.59 mmol/L (p = 0.501), potassium −0.034 mmol/L (p = 0.632), chloride −1.255 mmol/L (p = 0.479), and bicarbonate −1.060 mmol/L (p = 0.067). Table II

Table II.

Plasma electrolytes in study participants and reference values in normotensive pregnant participants.

Electrolytes	Normotensive Pregnant participants (n= 122) (Mean ± SD)	Preeclamptic participants (n= 100) (Mean ± SD)	Adjusted Mean Difference* (95% CI)	Reference values in Normotensive Pregnant participants (using Mean ± 2SD for upper and lower limit)**	p-value
Sodium (mmol/L)	136.93 ± 3.02	136.34 ± 6.55	-0.12 (-1.89 to 1.65)	130.89 – 142.97	0.657
Potassium (mmol/L)	3.61 ± 0.32	3.58 ± 0.56	-0.034 (-0.173 to 0.105)	2.99 – 4.25	0.639
Chloride (mmol/L)	108.75 ± 2.48	107.26 ±16.36	-1.255 (-4.740 to 2.230)	103.79 – 113.71	0.322
Bicarbonate (mmol/L)	21.56 ± 2.17	20.79 ± 4.87	-1.060 (-2.194 to 0.074)	17.22 – 25.90	0.119

Note: The t-test was used as the variables were normally distributed

* Adjusted mean difference (Pre-eclamptic minus Normotensive) after controlling for gestational age using multiple linear regression.

** Reference intervals were derived using the parametric method (mean ± 2SD) after confirming approximate normality with the Kolmogorov-Smirnov test

SD: Standard Deviation

n: number of participants

Mmol/L: Millimole per litre

Table III shows the pattern of electrolyte derangements. Hyponatraemia was significantly more prevalent in pre-eclamptic women (44.0% vs 27.87%, p = 0.018), and this difference remained highly significant after adjustment for gestational age (adjusted OR = 3.542, 95% CI 1.751–7.165, p < 0.001). Correspondingly, normonatraemia was significantly less common in the pre-eclamptic participants (adjusted OR = 0.305, p = 0.001). There were no significant differences between the groups in the prevalence of hypokalaemia, normokalaemia, hyperchloraemia, normochloraemia, or low bicarbonate levels after adjusting for gestational age (all p > 0.05). Elevated bicarbonate levels were observed only in the pre-eclamptic participants.

Table III:

Pattern of electrolyte derangement in study participants (unadjusted and adjusted for gestational age)

Electrolyte Abnormality	Normotensive (n=122)	Pre-eclamptic (n=100)	Unadjusted p-value (χ2)	Adjusted OR*(95% CI)	Adjusted p-value
Hyponatraemia	34 (27.87%)	44 (44.0%)	0.018	3.542 (1.751 – 7.165)	<0.001
Normonatraemia	86 (70.49%)	50 (50.0%)	0.006	0.305 (0.155 – 0.598)	0.001
Hypernatraemia	2 (1.64%)	6 (6.0%)	0.140	2.426 (0.308 – 19.105)	0.400
Hypokalaemia	49 (40.16%)	40 (40.0%)	1.000	0.874 (0.463 – 1.647)	0.676
Normokalaemia	73 (59.84%)	60 (60.0%)	1.000	1.145 (0.607 – 2.158)	0.676
Hyperchloraemia	64 (52.89%)	50 (50.0%)	0.818	0.536 (0.276 – 1.039)	0.065
Hypochloraemia	0 (0.00%)	2 (2.00%)	0.087	1.453 (0.923 – 2.783)	0.146
Normochloraemia	57 (47.11%)	48 (48.0%)	0.818	1.286 (0.689 – 2.403)	0.430
Low Bicarbonate	100 (81.97%)	77 (77.0%)	0.454	0.865 (0.379 – 1.973)	0.731
Normal Bicarbonate	22 (18.03%)	18 (18.00%)	0.989	0.981 (0.415 – 2.321)	0.966
Elevated Bicarbonate	0 (0%)	5 (5.0%)	0.051	2.652 3.164) (1.841 –	0.056

Note: Chi-Square test was used for comparison.

*Adjusted for gestational age using binary logistic regression.

OR = odds ratio in pre-eclamptic vs normotensive group.

Hypernatraemia – Plasma Sodium >145 mmol/L

Hyponatraemia – Plasma Sodium <136 mmol/L

Normonatraemia – Plasma Sodium 136-145 mmol/L

Hyperkalaemia – Plasma Potassium >5.2 mmol/L

Hypokalaemia – Plasma Potassium < 3.6 mmol/L

Normokalaemia – Plasma Potassium 3.6-5.2 mmol/L

Hyperchloraemia – Plasma Chloride >108 mmol/L

Hypochloraemia – Plasma Chloride < 94 mmol/L

Normochloraemia – Plasma Chloride 94-108 mmol/L

Elevated bicarbonate- Plasma bicarbonate > 32mmol/L

Low Bicarbonate- Plasma bicarbonate <24mmol/L

Normal bicarbonate – Plasma bicarbonate 24-32mmol/L

Sodium correlated with chloride (r = 0.241, p = 0.016) and bicarbonate (r = 0.479, p < 0.001). Potassium correlated with bicarbonate (r = -0.462, p < 0.001), systolic blood pressure (r = -0.338, p = 0.001), and diastolic blood pressure (r = -0.213, p = 0.033). No significant correlations were observed between sodium or chloride and blood pressure, and bicarbonate showed no significant correlation with blood pressure. Systolic and diastolic blood pressures were correlated (r = 0.595, p < 0.001). – Table IV.

Table IV:

Correlations between the electrolytes and blood pressure in pre-eclamptic participants

Variables	r-Value	P=value
Sodium and Potassium	0.113	0.263
Sodium and Chloride	0.241	0.016
Sodium and Bicarbonate	0.479	<0.001
Sodium and SBP	- 0.078	0.440
Sodium and DBP	- 0.144	0.154
Potassium and Chloride	0.148	0.141
Potassium and Bicarbonate	- 0.462	<0.001
Potassium and SBP	- 0.338	0.001
Potassium and DBP	- 0.213	0.033
Chloride and Bicarbonate	- 0.032	0.755
Chloride and SBP	0.111	0.274
Chloride DBP	0.128	0.205
Bicarbonate and SBP	0.106	0.294
Bicarbonate and DBP	- 0.060	0.552
SBP and DBP	0.595	<0.001

Note: Pearson’s Correlation was used

Discussion

This study evaluated serum electrolyte patterns among pre-eclamptic and normotensive pregnant women in Zaria and demonstrated that although mean electrolyte levels were not significantly different between the groups, clinically relevant abnormalities, particularly hyponatraemia, hypokalaemia, hyperchloraemia, and low bicarbonate, were prevalent, with a higher burden observed among pre-eclamptic participants. These findings highlight the complexity of electrolyte homeostasis in pre-eclampsia and underscore the importance of assessing both mean values and distribution patterns when evaluating biochemical derangements in pregnancy.

The absence of statistically significant differences in mean sodium, potassium, chloride, and bicarbonate levels between the groups aligns with findings by Chikezie K et al.⁴ in Calabar and similar Nigerian-based studies, which reported comparable electrolyte profiles between pre-eclamptic and normotensive women despite observable clinical abnormalities.¹³ This suggests that mean electrolyte values alone may mask clinically significant shifts occurring at the extremes of distribution. In contrast, studies from Ghana and Pakistan have reported significant reductions in sodium and potassium levels among pre-eclamptic women.^2,3 These discrepancies may be attributable to differences in study design, dietary habits, severity of disease, gestational age distribution, and laboratory methodologies.

A key finding in this study is the higher prevalence of hyponatraemia among pre-eclamptic participants (44.0%) compared to normotensive women (27.87%). This supports earlier reports linking hyponatraemia with pre-eclampsia severity and adverse outcomes.^6,14 Hyponatraemia in pre-eclampsia is thought to result from a combination of dilutional effects due to increased capillary permeability, inappropriate antidiuretic hormone (ADH) secretion, and impaired renal free water clearance.¹⁴ Additionally, endothelial dysfunction, a hallmark of pre-eclampsia, may exacerbate fluid shifts into the interstitial space, further lowering serum sodium concentration. These findings reinforce the prognostic importance of sodium monitoring in pre-eclamptic patients, even in the absence of significant changes in mean values.

Potassium levels were similarly not significantly different between groups; however, hypokalaemia was highly prevalent in both cohorts (approximately 40%). This finding is consistent with studies suggesting increased renal potassium loss during pregnancy, possibly exacerbated in pre-eclampsia due to secondary hyperaldosteronism and altered tubular handling.¹⁵ However, contrary findings have been reported in some studies where potassium levels were significantly lower in pre-eclamptic women, attributed to exaggerated RAAS activation and increased urinary potassium excretion.^3,16 The negative correlation observed between potassium and blood pressure in this study further supports the role of potassium in vascular tone regulation and suggests that lower potassium levels may contribute to increased vascular resistance in pre-eclampsia.

Interestingly, hyperchloraemia was highly prevalent in both groups, with no significant difference between them. This may reflect dietary patterns, fluid therapy practices, or physiological changes in chloride handling during pregnancy. Chloride is often overlooked in obstetric biochemical assessment; however, its role in acid–base balance is critical.¹⁷ The lack of significant correlation between chloride and blood pressure in this study suggests that chloride disturbances may be more reflective of systemic acid–base status rather than direct contributors to hypertensive pathology.¹⁸

A high proportion of participants in both groups had low bicarbonate levels. This finding reflects the well-documented physiological compensatory renal excretion of bicarbonate in response to progesterone-driven respiratory alkalosis of pregnancy rather than true metabolic acidosis.^9,19 The similarity in bicarbonate levels between pre-eclamptic and normotensive women further suggests that this compensatory process remains largely preserved in pre-eclampsia. Nonetheless, the degree of bicarbonate reduction may vary depending on disease severity, renal function, and environmental or nutritional factors, and thus should still be interpreted cautiously within the clinical context.¹⁹

The correlation analysis further provides insight into electrolyte interactions in pre-eclampsia. The positive correlation between sodium and bicarbonate suggests linked regulation through renal tubular mechanisms, while the inverse relationship between potassium and bicarbonate reflects known physiological interactions in acid–base balance, where acidosis promotes extracellular potassium shift.¹⁷ The observed negative correlation between potassium and blood pressure supports existing evidence that potassium has vasodilatory effects and may modulate vascular responsiveness, a factor that could influence hypertension severity in pre-eclampsia.¹⁵

Another important contribution of this study is the establishment of reference ranges for electrolytes in normotensive pregnant women in Zaria. These locally derived reference intervals (sodium: 130.89–142.97 mmol/L, potassium: 2.99–4.25 mmol/L, chloride: 103.79–113.71 mmol/L, bicarbonate: 17.22–25.90 mmol/L) differ slightly from conventional non-pregnant reference ranges, reinforcing the need for pregnancy-specific and region-specific reference values. Failure to use appropriate reference intervals may lead to misclassification of electrolyte abnormalities and inappropriate clinical decisions.

Overall, the findings of this study suggest that electrolyte disturbances in pre-eclampsia are more evident in distribution patterns rather than mean differences. This underscores the importance of individualized assessment and careful interpretation of biochemical data in pregnant women. The high prevalence of hyponatraemia and metabolic acidosis, in particular, highlights the need for routine electrolyte monitoring in antenatal care, especially in resource-limited settings where complications of pre-eclampsia remain a major cause of maternal morbidity and mortality.

Limitations

This study has some limitations that should be considered when interpreting the findings. First, its cross-sectional design limits the ability to establish causal relationships between electrolyte abnormalities and pre-eclampsia. Second, the study was conducted in a single tertiary centre in Zaria, which may limit the generalisability of the findings to other populations with different dietary patterns, environmental exposures, and healthcare practices. Additionally, dietary intake, hydration status, and hormonal parameters such as renin, aldosterone, and antidiuretic hormone, which could provide deeper insights into electrolyte regulation, were not assessed. Third, the significant difference in gestational age between groups (30.2 vs 35.7 weeks) is a potential confounder; future studies should match participants by gestational age or adjust using regression analysis. Finally, the use of point-of-care electrolyte analysis, although practical and rapid, may introduce minor variability compared to standard laboratory methods.

Conclusion

This study demonstrates that although mean serum electrolyte concentrations do not differ significantly between pre-eclamptic and normotensive pregnant women in Zaria. Clinically relevant electrolyte abnormalities, particularly hyponatraemia, are significantly more prevalent among pre-eclamptic participants. These findings underscore the importance of evaluating distribution patterns in addition to mean values when interpreting biochemical parameters in pregnancy. The observed reduction in bicarbonate levels is consistent with physiological renal compensation for pregnancy-induced respiratory alkalosis rather than true metabolic acidosis. Importantly, the derivation of local reference intervals highlights subtle variations from conventional ranges and reinforces the need for population- and pregnancy-specific benchmarks in clinical practice. However, interpretation of these findings should be cautious due to gestational age differences and other potential confounders. Further well-designed, gestational age-matched and longitudinal studies are recommended to better elucidate the temporal relationship between electrolyte alterations and the severity and outcomes of pre-eclampsia.

Acknowledgment

The authors wish to acknowledge The National Agency for the Control of AIDS, Nigeria, for donating the EDAN i15VET Blood Gas and Electrolyte Analyser as well as the cartridges used in this work.