INTRODUCTION

Magnesium is the second most common intracellular cation, doing an essential role in many physiologic functions. It is important in energy requiring metabolic processes, protein synthesis, membrane integrity, nervous tissue conduction, neuromuscular excitability, muscle contraction, hormone secretion and intermediate metabolism.[1] The normal plasma magnesium concentration is 1.5-2.3 mg/dl (1.2-1.9 meq/l; 0.62-0.94 m mol/l) with some variation between clinical laboratories.[2] Magnesium has been used as a tocolytic agent since 1969.[3] A randomized trial resulted magnesium sulfate could effectively prevent preterm birth.[4] Another study showed successful tocolysis in more than 92% of patients by using larger doses of magnesium sulfate.[5] In a study, 46% of pregnant mothers had deficiency of magnesium as exposed by serum level.[6]

It has been studied that intake of magnesium may be insufficient for many women during pregnancy.[7] However, it uses for eclampsia and sometime for preeclampsia.[8] Almone and colleague findings have implicated magnesium as being an essential element for fetal well-being and supplementation of magnesium may be benefited to fetal outcome.[9] Magnesium supplementation during pregnancy was associated with significantly fewer maternal hospitalizations, a reduction in preterm delivery, and less frequent referral of the newborn to the neonatal intensive care unit. The results suggest that magnesium supplementation during pregnancy has a significant influence on fetal and maternal morbidity both before and after deliver.[10] Trials have documented that oral supplementation of magnesium in physiological amounts during pregnancy reduces pregnancy hypertension, miscarriage, premature birth and fetal growth Retardation.[11]

Limited data is available on the nutritive effect of magnesium among pregnant mothers in Iran. The aim of this prospective case-controlled study was to determine the relationship between maternal magnesium concentrations and neonatal birth weight in a group of mothers having low birth weight (LBW) deliveries and compared with a group who delivered normal birth weight infants. If magnesium is found to be involved in the pathogenesis of LBW, then supplementation of magnesium during pregnancy could possibly be considered to ameliorate this serious morbidity.

METHODS

We conducted this prospective case-control study at the maternity ward since May 2006 for 1 year. The study protocol was approved by the research office and written informed consents were obtained from each subject before enrollment. Mother-infants pairs were included if a) maternal age was 17 to 35 years at the time of delivery, and b) she had uncomplicated singleton pregnancy.

“Cases” were considered if the birth weight of the newborn was <2500 g without any known underlying risk factors that could explain the reason for the LBW. A “Control” subject was enrolled when a subsequent mother delivered an infant with birth weight ≥2500 g.

Mothers were not considered for the study if any of the following exclusion criteria were present: A previous history of LBW delivery, twin and multiple pregnancies, pre-eclampsia and eclampsia, uterine cervical abnormalities, antenatal bleeding, oligo-and polyhydramnios, maternal disorders prior pregnancies; such as systemic lupus erythematosus, chronic hypertension, diabetes mellitus, seizure disorders, malignancies, and drug or alcohol abuse.[12]

The investigator did a thorough physical examination of every infant recruited into the study. The infant's weight was taken to the nearest 10 g and the length was recorded to the nearest 0.1 cm. The gestational age was assessed clinically by new Ballard score.[12] Medical and social data on mothers were obtained from available information in their records and by direct interviews.

In the first 24 h after delivery, blood from antecubital vein was drawn from the subjects and collected in previously labeled polypropylene tubes. Blood was transported in ice packs to the central laboratory for separation of serum. The samples were centrifuged at 3500 rpm at 4°C for 30 min for the collection of serum. Maternal serum magnesium was determined by the standard atomic absorption spectro-photometry method.[13]

All specimens were de-identified before processing, therefore, laboratory staff was masked to clinical conditions. The data were analyzed by using the SPSS version 11.5 software. If the data had normal distribution, analytic statistical methods were applied, including χ² for the qualitative variables and a student t-test for quantitative variables. Moreover, in the case of having had abnormal distribution, a nonparametric test was used. Multiple linear regression analysis was performed to control of potential confounding variables. Statistical significance was considered when P < 0.05.

RESULTS

One hundred and sixteen mothers have been included in study of that 67 mothers had neonate with birth weight more than 2,500 g (case) and 49 mothers had a neonate less than 2,500 g (control). The demographic and clinical characteristics of the population have been listed in Table 1.

Table 1. Demographic and clinical characteristic of the study population (n=116)

Mean concentrations of magnesium levels in case group was 0.86 ± 0.11 m mol/L, and mean magnesium levels in control group was 0.94 ± 0.22 m mol/L. There is no significant difference between two groups. (P = 0.09)

We divided cases in two groups. Forty-five mothers who have low birth weight infants (1,500 to 2,499 g) and 22 mothers who have very low birth weight infants (less than 1500 g). Mean concentrations of magnesium levels in mothers with LBW was 0.88 ± 0.12 m mol/L. There is no significant difference between two groups too (P = 0.39).

We tried to show difference between magnesium levels of 22 mothers, with very low birth weight infants and 49 mothers with normal weight infants (2,500 g more). However, there is no difference also (P = 0.47).

On regression analysis, magnesium concentrations do not differ significantly between cases and controls after we controlled them for various confounders such as maternal age, body mass index, educational levels, income, neonatal gender, birth weight, gestational age and Apgar score.

There are not correlations between mean concentrations of magnesium levels and birth weight (R = 0.14, P = 0.12), and gestational age (R = 0.17, P = 0.15).

DISCUSSION

Magnesium is an ion with several reactions in human body. Therefore, variations in its concentrations, beyond physiologic levels, can have important clinical repercussions. In order to identity these changes, it is necessary to have standard references. The presence of upsets in intrauterine nutrition, such as intrauterine growth retardation can potentially lead to deviations in the homeostasis of magnesium, which have not yet fully clarified.[14]

In a study was demonstrated magnesium status was not associated with risk of low birth weight.[15] The meta-analysis of some trials indicated that oral magnesium treatment from before the twenty-fifth week of gestation resulted in lower frequencies of preterm birth, low birth weight and small for gestational age compared with placebo treatment.[16] A double blind study by Saibai and colleague showed a positive correlation between magnesium intakes in the first trimester of pregnancy with the birth weight. But, magnesium supplementation during II and III trimester had no effect on the outcome of pregnancy.[17]

Nutritional magnesium therapy is useful for prevention of prematurity.[18] In this study, results show there are not difference significantly between mothers with low birth weight and normal weight infants. This could be related to the recent mandate by the ministry of health in our country to provide multivitamins and minerals supplementations to all pregnant women. The present study indicate a need of longitudinal studies with larger sample size need to be undertaken in different parts of the country to assess the magnitude of element deficiencies amongst pregnant mothers.