ABSTRACT
Pregnancy and lactation are normal but stressful physiological phenomena during which many biochemical changes occur, including calcium and phosphate metabolism, which may lead to calcium deficiency in pregnant women. Also the oxidative stress (ODS) associated with pregnancy and lactation induces increased activity of biomarkers of ODS. Since data on the serum levels of calcium, phosphate and ODS biomarkers in women in Zaria are scanty, the evaluation of their serum profiles in pregnant and lactating women in Zaria will provide reference data for clinicians and other medical workers involved in routine antenatal care in Nigeria and other resource limited third world countries. The aim of this study was to evaluate the changes in serum levels of calcium, phosphate, vitamin D and their regulatory hormones and serum antioxidant status of pregnant women in Zaria, Nigeria. In this study, blood samples were collected and anthropometric measurements such as weight, height and body mass index (BMI) of 179 women were taken. The women were grouped into: non-pregnant women: control group (n = 45), pregnant women in the first trimester (n = 45), pregnant women in the second trimester (n = 45), pregnant women in the third trimester (n = 45) and lactating women (n = 30). Serum was obtained from the blood samples and assayed for calcium, phosphate, vitamin D, parathyroid hormone, calcitonin, antioxidant biomarkers (superoxide dismutase, catalase and glutathione peroxidase) and lipid peroxidation biomarker (malondialdehyde) using standard methods. Data were presented as mean  SD. Analysis of data was performed using one-way analysis of variance (ANOVA) to find the significance between the groups, followed by Holm-Sidak post-hoc test. Pearson's correlation analysis was used to determine the inter-relationship between the variables and values of p ≤ 0.05 were considered significant. Statistical package used was Minitab statistical software version 16. The results revealed that there was a significant decrease in serum calcium concentration (p < 0.01) during the third trimester of pregnancy and during lactation. There was increased serum concentration of vitamin D, parathyroid hormone and calcitonin in the 2nd trimester which were decreased during the third trimester and lactation, these findings were not significant when they were compared with the control. Only 1.76% of hypocalcaemia was observed in the study population and 21.24% of hypervitaminosis D was observed. There was a negative correlation observed between serum calcium concentration and gestational age (r = 0.255) which was significant (p < 0.01). There was no correlation observed between gestational age and serum phosphate concentration. Lipid peroxidation was highest in the lactating women since serum malondialdehyde concentration was highest here, and it was significant when compared with the control. Serum superoxide dismutase and glutathione peroxidase concentrations were significantly higher during lactation when compared with the control (p < 0.05). There was significant negative correlation (r = -0.580, p = 0.001) between serum malondialdehyde concentration and serum glutathione peroxidase concentration. There was also a significant positive correlation between serum superoxide dismutase and vitamin D concentrations (r = 0.175, p < 0.05), serum glutatathione peroxidase and vitamin D concentrations (r = 0.227, p < 0.01) and serum malondialdehyde and phosphate concentrations (r = -0.189, p = 0.05). There was no significant difference observed in the mean serum concentrations of calcium, phosphate, vitamin D, parathyroid hormone and calcitonin between the age groups. There was also no significant difference in the mean serum concentrations of calcium, phosphate, vitamin D, parathyroid hormone and calcitonin on parity when compared with the control. No significant difference was also observed when serum concentration of calcium, phosphate, vitamin D, parathyroid hormone and calcitonin were compared among the ethnic groups although serum calcitonin concentration appeared highest among the Hausa ethnic group, while serum concentration of catalase was highest among the Yorubas. Serum calcium concentrations appeared to be highest among women who did handwork, though not significant. Serum concentration of malondealdehyde was highest in house wives though not significant. BMI and residential location did not seem to affect serum concentrations of all the parameters. Based on the findings of this study, it was concluded that there was very low prevalence of serum calcium, phosphate and vitamin D deficiency in pregnant and lactating women in Zaria; even though the serum concentration of calcium decreased across the trimesters and lactation, malondialdehyde concentration increased during lactation, while superoxide dismutase activity and reduced glutathione concentration were significantly higher. Local base-line reference values for calcium, phosphate, vitamin D, parathyroid hormone and calcitonin for pregnant women and a predictive equation for the serum calcium levels during pregnancy and the period of lactation were established in the study
