Am J Perinatol
DOI: 10.1055/s-0043-1776902
SMFM Fellows Research Series

The Effect of Body Mass Index on Post-Bolus Magnesium Levels in the Obstetric Patient

1   Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, University of California Irvine, California
,
1   Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, University of California Irvine, California
,
1   Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, University of California Irvine, California
,
1   Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, University of California Irvine, California
› Author Affiliations
Funding None.

Abstract

Objective In the setting of a growing obese obstetric population, we sought to determine whether differences in body mass index (BMI) and obesity class influenced both serum magnesium levels and the likelihood of achieving therapeutic levels for eclampsia prophylaxis after standard boluses of magnesium sulfate.

Study Design This is a retrospective cohort study of patients treated with magnesium sulfate in the setting of either preeclampsia with severe features or preterm labor between 2010 and 2016. Subjects were categorized by BMI: Normal (BMI < 30 kg/m2), Class 1 (BMI 30–34.9 kg/m2), Class 2 (BMI 35–39.9 kg/m2), and Class 3 (BMI ≥ 40 kg/m2). Study participants' demographics, intrapartum characteristics, and adverse reactions were compared among the groups. Logistic regression models were used to calculate unadjusted and adjusted odds ratios comparing the likelihood of each BMI class reaching therapeutic eclamptic prophylactic levels. Linear regression models were also evaluated to determine the relationship between BMI and post-bolus serum magnesium levels.

Results Of the 760 people who met the inclusion criteria, 313 (41.1%) had normal BMI, 190 (25.0%) had Class 1 obesity, 135 (17.8%) had Class 2 obesity, and 122 (16.1%) had Class 3 obesity. When adjusted for confounders, those with Class 1 obesity were 54% less likely to achieve serum levels deemed therapeutic for seizure prophylaxis compared with normal BMI counterparts. Meanwhile, those with Class 2 or 3 obesity were 90% less likely. Linear regression models also demonstrated an inverse association between BMI and post-bolus serum magnesium levels.

Conclusion Increasing BMI has a significant effect on post-bolus serum magnesium levels regardless of standard loading dose used. Immediately after bolus administration, obese gravidas are significantly less likely to reach levels effective for eclamptic seizure prophylaxis. When considering which bolus to administer in an obese gravida, it may be more beneficial to choose a 6 g load.

Key Points

  • BMI has an inverse relationship with post-bolus serum magnesium levels.

  • Obese gravidas were less likely to reach eclampsia prophylaxis levels regardless of bolus type.

  • Obesity class, not just the presence or absence of obesity, plays a role in serum magnesium levels.

Note

This research was previously presented as a poster presentation at the 42nd Annual Pregnancy Meeting (virtual), Society for Maternal-Fetal Medicine, January 31, 2021 to February 5, 2022.




Publication History

Received: 15 August 2021

Accepted: 22 October 2023

Article published online:
10 November 2023

© 2023. Thieme. All rights reserved.

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  • References

  • 1 Fishel Bartal M, Sibai BM. Eclampsia in the 21st century. Am J Obstet Gynecol 2022; 226 (2S): S1237-S1253
  • 2 The American College of Obstetricians and Gynecologists. Committee Opinion No. 455: Magnesium sulfate before anticipated preterm birth for neuroprotection. Obstet Gynecol 2010; 115 (03) 669-671
  • 3 American College of Obstetricians and Gynecologists Committee on Obstetric Practice Society for Maternal-Fetal Medicine. Committee Opinion No. 573: Magnesium sulfate use in obstetrics. Obstet Gynecol 2013; 122 (03) 727-728
  • 4 Espinoza J, Vidaeff A, Pettker CM, Simhan H. Gestational Hypertension and Preeclampsia: ACOG Practice Bulletin Summary, Number 222. Obstet Gynecol 2020; 135 (06) 1492-1495
  • 5 Duley L. The global impact of pre-eclampsia and eclampsia. Semin Perinatol 2009; 33 (03) 130-137
  • 6 Say L, Chou D, Gemmill A. et al. Global causes of maternal death: a WHO systematic analysis. Lancet Glob Health 2014; 2 (06) e323-e333
  • 7 Altman D, Carroli G, Duley L. et al; Magpie Trial Collaboration Group. Do women with pre-eclampsia, and their babies, benefit from magnesium sulphate? The Magpie Trial: a randomised placebo-controlled trial. Lancet 2002; 359 (9321) 1877-1890
  • 8 Cruikshank DP, Pitkin RM, Reynolds WA, Williams GA, Hargis GK. Effects of magnesium sulfate treatment on perinatal calcium metabolism. I. Maternal and fetal responses. Am J Obstet Gynecol 1979; 134 (03) 243-249
  • 9 Zuspan FP. Treatment of severe preeclampsia and eclampsia. Clin Obstet Gynecol 1966; 9 (04) 954-972
  • 10 Sibai BM, Lipshitz J, Anderson GD, Dilts Jr PV. Reassessment of intravenous MgSO4 therapy in preeclampsia-eclampsia. Obstet Gynecol 1981; 57 (02) 199-202
  • 11 Flowers Jr CE, Easterling Jr WE, White FD, Jung JM, Fox Jr JT. Magnesium sulfate in toxemia of pregnancy. New dosage schedule based on body weight. Obstet Gynecol 1962; 19: 315-327
  • 12 Rouse DJ, Hirtz DG, Thom E. et al. A randomized, controlled trial of magnesium sulfate for the prevention of cerebral palsy. 2008 359. . Accessed April 27, 2023 at: www.nejm.org
  • 13 Crowther CA, Hiller JE, Doyle LW, Haslam RR. Effect of magnesium sulfate given for neuroprotection before preterm birth a randomized controlled trial. Accessed April 27, 2023 at: https://jamanetwork.com/
  • 14 Leetheeragul J, Boriboonhirunsarn D, Reesukumal K, Srisaimanee N, Horrasith S, Wataganara T. A retrospective review of on-admission factors on attainment of therapeutic serum concentrations of magnesium sulfate in women treated for a diagnosis of preeclampsia. J Matern Fetal Neonatal Med 2020; 33 (02) 258-266
  • 15 Tudela CM, McIntire DD, Alexander JM. Effect of maternal body mass index on serum magnesium levels given for seizure prophylaxis. Obstet Gynecol 2013; 121 (2 Pt 1): 314-320
  • 16 Brookfield KF, Tuel K, Rincon M, Vinson A, Caughey AB, Carvalho B. Alternate dosing protocol for magnesium sulfate in obese women with preeclampsia: a randomized controlled trial. Obstet Gynecol 2020; 136 (06) 1190-1194
  • 17 Dayicioglu V, Sahinoglu Z, Kol E, Kucukbas M. The use of standard dose of magnesium sulphate in prophylaxis of eclamptic seizures: do body mass index alterations have any effect on success?. Hypertens Pregnancy 2003; 22 (03) 257-265
  • 18 Brookfield KF, Su F, Elkomy MH, Drover DR, Lyell DJ, Carvalho B. Pharmacokinetics and placental transfer of magnesium sulfate in pregnant women. Am J Obstet Gynecol 2016; 214 (06) 737.e1-737.e9
  • 19 Vilchez G, Dai J, Lagos M, Sokol RJ. Maternal side effects and fetal neuroprotection according to body mass index after magnesium sulfate in a multicenter randomized controlled trial. J Matern Fetal Neonatal Med 2018; 31 (02) 178-183
  • 20 McPherson J, Smiley S, Stamilio D. Maternal obesity and neuroprotective magnesium sulfate. Am J Obstet Gynecol Mosby Inc.; 2015; 213: 582.e1-582.e6
  • 21 American College of Obstetricians and Gynecologists' Committee on Practice Bulletins–Obstetrics. Obesity in Pregnancy: ACOG Practice Bulletin, Number 230. Obstet Gynecol 2021; 137 (06) e128-e144
  • 22 American College of Obstetricians and Gynecologists' Committee on Practice Bulletins—Obstetrics. ACOG Practice Bulletin No. 203: Chronic Hypertension in Pregnancy. Obstet Gynecol 2019; 133 (01) e26-e50
  • 23 Weiss JL, Malone FD, Emig D. et al; FASTER Research Consortium. Obesity, obstetric complications and cesarean delivery rate–a population-based screening study. Am J Obstet Gynecol 2004; 190 (04) 1091-1097
  • 24 Pritchard JA. Changes in the blood volume during pregnancy and delivery. Anesthesiology 1965; 26: 393-399
  • 25 Hales CM, Carroll MD, Fryar CD, Ogden CL. Prevalence of obesity and severe obesity among adults: United States, 2017–2018. NCHS Data Brief 2020; (360) 1-8