Hemodynamic Changes, Serum Calcium, Magnesium Levels, and relationship with uterine contractility among postpartum women in Kabutare District Hospital in Rwanda: A Cross-Sectional Study

Technical Summary: Hemodynamic Changes, Serum Calcium, Magnesium Levels, and Relationship with Uterine Contractility in Postpartum Women in Rwanda

Problem Statement
Postpartum hemorrhage (PPH) remains a leading cause of maternal morbidity and mortality globally, particularly in low- and middle-income countries where uterine atony accounts for 70–80% of cases. While the physiological mechanisms of uterine contraction rely heavily on calcium-mediated excitation–contraction coupling and the regulatory role of magnesium, there is a scarcity of data linking maternal electrolyte status (specifically serum calcium and magnesium) to uterine contractility and hemodynamic stability in the immediate postpartum period within sub-Saharan Africa. Existing literature often focuses on obstetric risk factors without simultaneously evaluating the physiological contribution of electrolyte imbalances to PPH in Rwandan settings.

Methodology
This hospital-based cross-sectional study was conducted at Kabutare District Hospital in Rwanda, involving 99 postpartum women (after exclusions from an initial recruitment of 100).

• Participants: Women aged 17–45 years with singleton term pregnancies (≥37 weeks) delivered via vaginal or cesarean section. Exclusion criteria included chronic renal/metabolic disorders, coagulation issues, severe anemia, and prior use of magnesium sulfate or blood transfusions.
• Data Collection:
  • Electrolytes: Venous blood samples were collected within one hour of delivery to measure total serum calcium and magnesium using a COBAS chemistry analyzer.
  • Clinical Assessments: Uterine tone was assessed via abdominal palpation at 15 minutes, 30 minutes, 1 hour, 4 hours, and 24 hours, classified as firm, moderate, or boggy.
  • Hemodynamics: Blood pressure (systolic and diastolic) and pulse rate were measured using a calibrated digital sphygmomanometer at 0, 4, 8, 12, 16, 20, and 24 hours postpartum.
  • Blood Loss: Quantified using the gravimetric method (weighing blood-soaked materials), with PPH defined as ≥500 mL (vaginal) or ≥1000 mL (cesarean) within 24 hours.
• Statistical Analysis: Data were analyzed using SPSS version 25. Associations were tested using Chi-square/Fisher's exact tests, correlations via Pearson/Spearman coefficients, and predictors of PPH were identified using multivariable logistic regression. Significance was set at p < 0.05.

Key Results

• Electrolyte Prevalence: 16.2% of participants exhibited hypocalcemia, and 8.1% had combined hypocalcemia and hypomagnesemia. No cases of isolated hypomagnesemia were observed.
• Association with PPH: PPH occurred in 9.1% of participants (n=9). Women with combined electrolyte abnormalities had a significantly higher rate of PPH (37.5%) compared to those with normal levels (4.0%; p = 0.003).
• Electrolyte Levels in PPH vs. Non-PPH: Women with PPH had significantly lower mean serum calcium (7.7 ± 0.97 mg/dL vs. 9.0 ± 0.89 mg/dL; p < 0.001) and magnesium (1.8 ± 0.1 mg/dL vs. 2.2 ± 0.22 mg/dL; p < 0.001) compared to non-PPH women.
• Uterine Tone: A "boggy" uterus at 15 minutes postpartum was a critical predictor. Women with a boggy uterus experienced more than double the mean blood loss (733.0 mL vs. 321.4 mL) compared to those with a firm uterus. All 9 PPH cases occurred in women with a boggy uterus at 15 minutes.
• Hemodynamic Correlations: Serum calcium showed a significant negative correlation with pulse rate (r = −0.42) and a positive correlation with systolic blood pressure (r = 0.28). Magnesium showed a negative correlation with pulse rate (r = −0.36) and a positive correlation with diastolic blood pressure (r = 0.25).
• Predictors of PPH: Logistic regression identified hypocalcemia (AOR = 2.41), hypomagnesemia (AOR = 2.13), and a boggy uterus at 15 minutes (AOR = 8.92) as significant independent predictors of PPH. Cesarean section and parity >3 were not independent predictors after adjustment.

Significance and Claims
The study claims that reduced serum calcium and magnesium levels are significantly associated with impaired uterine contractility, altered hemodynamic parameters, and an increased risk of postpartum hemorrhage. The authors posit that maternal electrolyte status contributes to PPH independently of conventional obstetric risk factors.

The paper suggests that the assessment of maternal electrolyte status, combined with early clinical evaluation of uterine tone (specifically at 15 minutes postpartum), could facilitate the early identification of women at increased risk for PPH. This approach is highlighted as potentially valuable for improving maternal care in resource-limited settings where advanced monitoring may be unavailable.

Limitations and Modesty of Claims
The authors explicitly acknowledge several limitations that temper the generalizability of their findings:

• Study Design: The cross-sectional nature restricts causal inference.
• Sample Size: The small number of PPH events (n=9) means the logistic regression models are exploratory and subject to potential overfitting; the adjusted odds ratios require validation in larger cohorts.
• Measurement Constraints: Only total calcium was measured, not ionized calcium, and serum albumin was not measured to correct for protein binding, which could affect the accuracy of hypocalcemia rates.
• Generalizability: As a single-center study in a district hospital, the findings may not be representative of all postpartum women in Rwanda.

Consequently, the authors conclude that while their findings support the physiological importance of electrolytes in postpartum hemostasis, these results should be interpreted cautiously and validated through larger, multicenter studies before being generalized to the wider Rwandan population or used to mandate new clinical protocols.