Ionized Serum Magnesium Levels in Umbilical Cord Blood of Normal Pregnant Women at Delivery: Relationship to Calcium, Demographics, and Birthweight

Abstract

Using a novel ion-selective electrode for ionized Mg (IMg2+), we sought to: (1) determine levels and fractions of IMg2+ in umbilical vessels of normal pregnant women: (2) determine their relationships with ionized calcium (ICa2+) levels: (3) determine whether any demographic or clinical parameters affect these levels of divalent cations: and (4) compare levels of IMg2+, total Mg, percent IMg2+, and ICa2+ with sera of normal pregnant and nonpregnant women. We obtained umbilical arterial and venous serum from 38 normal subjects and venous samples from 26 normal pregnant women and 42 nonpregnant women. The mean umbilical venous IMg2+ level (0.51 +/- 0.01 mmol/liter) was significantly greater than the umbilical arterial level (0.48 +/- 0.01 mmol/liter, p < 0.05), and the latter was similar to maternal venous levels (0.48 +/- 0.01 mmol/liter). The maternal venous mean value is 20% less than that found (0.60 +/- 0.005 mmol/liter) in peripheral serum of nonpregnant women. The ionized fractions were significantly (p < 0.01) higher in the umbilical veins than umbilical arteries, and the percent IMg2+ fractions were similar in umbilical arteries and maternal venous blood. IMg2+ levels were lower in multiparous patients and those who received epidural analgesia and higher in patients who had operative vaginal delivery and in Asians. Ionized fractions of Mg in umbilical veins were higher in large for gestational age infants. Our findings provide evidence of a Mg deficiency in pregnancy and suggest that measurement of IMg2+ may have clinical value for diagnosis and therapy of such deficiency.(ABSTRACT TRUNCATED AT 250 WORDS)

Circulating Divalent Cations in Asymptomatic Ovarian Hyperstimulation and in vitro Fertilization Patients

“…Our present results confirm and extend previous studies [3,5] and point most strongly to the facts that the hemodynamically and otherwise important biologically active divalent cation magnesium and the ionized Ca/Mg ratio circulating in the blood are somehow intimately related to the sex hormone levels in women, whether they are normal adults of child-bearing age [3], post-menopausal [5], pregnant [7][8][9][10][11] or pharmacologically altered (present study).…”

“…The Ca 2+ /Mg 2+ ratios were calculated (using the measured Ca 2+ and Mg 2+ values), as was the percent ionized Mg 2+ . The normal reference ranges for our laboratory are as follows: Ca 2+ 1.09-1.33 mmol/l; Mg 2+ 0.54-0.64 mmol/l; total Mg 0.74-0.96 mmol/l [7].…”

Evaluation of Plasma Ionized Magnesium Levels in Neonatal Hyperbilirubinemia

“…In two studies performed on pediatric intensive care patients (32) and 22 newborns with hypomagnesemia (33), it was shown that serum total Mg levels may not correlate with IMg levels and that IMg measurement best provides a more relevant assessment of Mg homeostasis. In one of the initial studies conducted by using ISE method in umbilical cord blood samples, Handwerker et al (24) reported umbilical venous IMg levels (0.49 -0.53 mM) a little higher than umbilical arterial ones (0.46 -0.5 mM). In another study aiming to determine normative data in healthy term newborns (22), IMg levels were investigated in umbilical venous blood of 30 newborns at birth and in peripheral venous blood of 32 newborns at 24 h of life, and normal ranges of IMg in both groups reportedly were between 0.4 and 0.56 mM.…”

“…Although these levels are similar and close to those in the previously published studies on newborns, the relatively wider ranges in our study may have resulted from the mean postnatal age (156.1 Ϯ 46.5 h) of the cases, considering physiologic changes in Mg levels during the first week of life. Previously published neonatal IMg studies (22)(23)(24) have been conducted in exclusively healthy newborns during the first 24 -72 h of life. The high serum bilirubin levels also may have contributed to greater variability of IMg; high IMg levels (0.6 Ϯ 0.12 mM) in the group of severe hyperbilirubinemia in our study further supports this hypothesis.…”

“…Comparisons between these two groups were performed with independent sample t test. Comparisons and assessment of the relationship between the plasma IMg levels above the critical level of 0.69 mM, which has reportedly been the upper limit of normal in healthy term newborns (22)(23)(24), and the critical serum bilirubin levels of significant (Ն205 M) (21) and severe (Ն290 M) (25, 26) hyperbilirubinemia were made using 2 test. Parameters with nominal values such as sex and mode of delivery were compared with 2 test.…”