This cross-sectional study was conducted from December 2017 to March 2018. Permission from Institutional Ethical Committee was got before starting the study (Proposal No: 350/IHEC/10-17). Blood samples were collected from 240 pregnant women who attended the Obstetrics and Gynaecology Department of Chettinad Hospital and Research Institute. Among them three patients had pre-eclampsia, 14 had gestational diabetes mellitus, 29 had hypothyroidism, 56 women complained of leg cramps, 62 had previous history of abortions. All subjects were explained about the purpose of the study and if willing to participate, informed consent was obtained from all the participants in the study. The power of the study was 80% with 90% confidence interval. Demographic details were collected from all the subjects.

Pre-eclampsia diagnosed as BP levels more than 140/90 mm of Hg with proteinuria, Gestational Diabetes Mellitus (diagnosed by Oral Glucose Tolerance Test (OGTT) by Diabetes in Pregnancy Study Group of India guidelines) [11] thyroid disorders (abnormal thyroid hormone levels), anaemia (Hb levels less than 11g.dl) and frequent episodes of leg cramps. Personal history was taken. Height and weight were measured for each candidate and Body Mass Index (BMI) was calculated using the formula BMI=weight (kg)/height (m²). Details regarding Socio-economic status, dietary pattern, previous obstetric history were obtained.

All pregnant women of the age group 18-35 years attending the Obstetric and Gynaecology OPD were included in the study. Subjects with endocrine disorders, kidney disease, peptic ulcer disease, chronic hypertension, history of intrauterine growth restriction, acquired immune deficiency syndrome, sickle cell anaemia, retroviral infections were excluded from the study.

Peripheral venous blood (5 mL) was collected each in red top vaccutainer (BD vacationer) for estimating magnesium levels and 5 ml in violet colored vaccutainer for estimating the amount of haemoglobin. After extraction, the sample in red topped vaccutainer was centrifuged at 2000 rpm for five minutes to separate the serum and was stored at -80 degree celcius for further analysis. Violet topped vaccutainer was sent to pathology laboratory for estimation of haemoglobin.

Magnesium can be analysed in blood using methods like Atomic absorption spectrophotometry, Ion selective electrodes and by using semi autoanalyser, but in all these methods, there will be interferences from other minerals and is less sensitive. In this study we have analysed magnesium levels in serum using auto-analyser [12]. Magnesium was analysed using the Methylthymol blue method and was run in Seimens Dimension RXL automated machine in the Biochemistry laboratory. Increased haemoglobin levels, bilirubin levels, and lipemic samples can falsely increase the magnesium levels in serum. Haemoglobin was analysed using cyan methhaemoglobin method in the Pathology laboratory in Beckman coulter automated machine.

Statistical analysis has been carried out using SPSS (Statistical Package for Social Sciences. (IBM version 21.0) software. The p-value less than 0.05 was considered statistically significant. Continuous variables were presented in the form of mean±SD and categorical variables were presented in the form of percentages. Pearsons correlation analysis was done to find out the correlation between magnesium, age, and BMI. Student’s t-test was used to compare the levels of magnesium among the groups with and without complications. ANOVA test was used to compare the three trimesters. ANOVA test was done to compare the mean of the continuous variables among the women in the first, second and third trimesters of pregnancy.

Among the 240 women enrolled for the study, more than 50% of the women had an educational qualification above higher secondary grade. About 85.83% of the women were housewives and 14.17% were working women. A 53.75% were primi, 33.3% were in second gravida, 10.42% in the third gravida and 2.5% in the fourth gravida. A 25.83% of women had previous history of abortion and 74.17% of women did not had any history of abortion [Table/Fig-1]. The 240 patients were divided into three groups based upon the trimesters in which they presented. The Mean values for magnesium among the first trimester patients were 2.96±0.83, for second trimester 2.99±1.48, and third trimester 3.05±1.48. ANOVA analysis showed that magnesium level showed no significant difference in between three groups [Table/Fig-2].

Magnesium levels in working women were found to be higher (3.12 mg/dL) than housewives (2.98 mg/dL) but it was not statistically significant. BMI was found to be 26±3.4 among working women and 28.4±4.22 among housewife. Haemoglobin levels were 10.82±1.11 among working women and 11.31±1.13 among house wives [Table/Fig-3].

Women with previous abortions were found to have less magnesium levels (2.71 mg/dL) compared to women without a history of abortion (3.11 mg/dL) and value was found to be statistically significant (p<0.007) [Table/Fig-4].

Magnesium levels among vegans (2.45) were lower than non vegans (3.08) and it was found to be statistical significant (p=0.013). BMI was found to be 24.57±3.37 among vegans and 25.43±4.23 among non vegetarians. Haemoglobin levels were 10.89±1.40 among vegans and 11.26±1.11 among non vegetarians [Table/Fig-5].

In this study, it was found that as the parity of the women increased magnesium level decreased, highest value was found among the primigravida (3.02) but there was no significant difference between the groups [Table/Fig-6].

Pearson correlation analysis done between magnesium and age showed a negative correlation coefficient of -0.064, which was not statistically significant [Table/Fig-7].

[Table/Fig-7]:

Pearson’s correlation between age and magnesium levels among pregnant women.

X axis: Age in years; Y axis: Magnesium levels (mg/dL)

Pearsons correlation analysis between magnesium and BMI showed a negative correlation coefficient of -0.0016 which was not statistically significant [Table/Fig-8].

[Table/Fig-8]:

Pearson’s correlation between BMI and magnesium levels among pregnant women.

X axis: BMI; Y axis: Magnesium levels (mg/dL)

There was no significant difference in the magnesium levels among pregnant women with complications and those without complications [Table/Fig-9].

Magnesium has established role in obstetrics, it being an essential element to fetal well-being. Deficiency of magnesium may be possibly associated with pre-eclampsia, abortion, preterm birth, leg cramps [13]. The formation of new tissues (maternal and fetal) during pregnancy requires high magnesium intakes than normal women of comparable age [14].

In present study, there was no significant difference in the mean levels of magnesium among the first, second and third trimesters. In a study done by Shaikh K et al., out of 150 patients, 60 patients in second trimester and 40 patients in the third trimester had low magnesium values (below reference range of 1.8 mEq/L), remaining had serum magnesium level within normal range of 1.8-2.9 mg/dL [15].

Larsson A et al., found that magnesium reference range was 1.2-2.3 mg/dL. They divided the patients into six groups based on gestational age as 7-17 weeks (1.6-1.7 mg/dL), 17-24 weeks (1.5-1.6 mg/dL), 24-28 weeks (1.5-1.53 mg/dL), 28-31 weeks (1.5-1.55 mg/dL), 31-34 weeks (1.55 mg/dL), 34-38 weeks (1.2-1.5 mg/dL) (149), but the drawback of the study was that the study population was very less (52 patients) [16].

Pathak P et al., showed that among 259 pregnant women, 113 had lower serum magnesium levels (<1.8mg/dL) when compared with normal healthy control patients [17]. They estimated serum magnesium by the standard atomic absorption spectrophotometric method. Atomic absorption spectrophotometer is considered as the best method for the estimation of serum magnesium [18], so that may be the cause for the disparity in the values.

The present study shows a decreased level of magnesium among women who had a history of abortion (2.71) compared to women who did not had a past history of abortion (3.11) and it was found to be statistically significant (p<0.007). Magnesium deficiency during pregnancy may interfere with fetal growth and development and has proven to cause a range of morbidity from haematological to teratogenic damages [19]. Magnesium promotes myometrial activity by modulating calcium uptake, binding and distribution in smooth muscle cells, hence magnesium deficiency during pregnancy can lead to increased uterine excitability [20].

Alnakash AH et al., conducted a study on 82 pregnant patients and their serum magnesium level was significantly low (p-value <0.012) in the women who had a history of abortion (1.597) than the control group (1.682) [21].

In present study, pregnant women who are non vegetarians had a more mean magnesium level (3.08) than the vegans (2.45). Magnesium levels are less in the food consumed by vegetarians and those belonging to the low socioeconomic groups than non vegetarians and those belonging to higher socio economic groups. Diet rich in protein increases magnesium absorption. Socioeconomic status affected serum magnesium levels significantly in term as well as preterm group, the values being lowest for women belonging to low socioeconomic status. These observations are similar to those reported by Franz KB and Potnis AV et al., [22,23].

Sharma A et al., showed that non vegetarians had a high serum magnesium levels (3.0) when compared to vegan pregnant women (2.29) [24] which is on par with our results.

The sample size of the study is small. Another limitation is that only one trace element was analysed in this study.

The present study shows that there is no significant difference in the magnesium levels among women in the three trimesters. It also points out that dietary patterns, socioeconomic status and parity of women play an important role in maintaining the levels of magnesium among pregnant women. This study points out the importance of maintaining proper levels of magnesium among pregnant women.