Effect of magnesium prophylaxis and preeclampsia on the duration of labor

Investigation of Intrapartum Parenteral Magnesium Sulfate as an Independent Risk Factor for Postpartum Hemorrhage Using Quantitative Blood Loss Assessment

BACKGROUND

Magnesium sulfate is used for seizure prophylaxis in preeclampsia and for fetal neuroprotection when delivery is anticipated before 32 weeks of gestation. Existing risk assessment tools for postpartum hemorrhage often identify the use of magnesium sulfate as an intrapartum risk factor. Previous studies examining the association between the use of magnesium sulfate and postpartum hemorrhage have relied largely on qualitative estimates of blood loss rather than quantitative estimates of blood loss.

OBJECTIVE

This study aimed to determine whether intrapartum administration of magnesium sulfate is associated with an increased risk of postpartum hemorrhage using a quantitative blood loss assessment via the use of graduated drapes and weight differences in surgical supplies.

STUDY DESIGN

This case-control study was conducted to test the hypothesis that intrapartum parenteral administration of magnesium sulfate is not independently associated with postpartum hemorrhage. All deliveries at our tertiary-level academic medical center between July 2017 and June 2018 were reviewed. Of note, 2 categories of postpartum hemorrhage were defined: the traditional definition (>500 mL for vaginal delivery and >1000 mL for cesarean delivery) and the contemporary definition (>1000 mL regardless of delivery mode). Statistical analyses using the chi-square test, Fisher exact test, t test, or Wilcoxon rank-sum test were performed to compare the patients who did and did not receive magnesium sulfate concerning the rates of postpartum hemorrhage, pre- and postdelivery hemoglobin level, and rates of blood transfusion.

RESULTS

A total of 1318 deliveries were included, with postpartum hemorrhage rates of 12.2% (traditional definition) and 6.2% (contemporary definition). Multivariate logistic regression did not find the use of magnesium sulfate as an independent risk factor by either definition (odds ratio, 1.44 [95% confidence interval, 0.87-2.38] and 1.34 [95% confidence interval, 0.71-2.54]). The only significant independent risk factor was cesarean delivery, by both definitions (odds ratio, 2.71 [95% confidence interval, 1.85-3.98] and 19.34 [95% confidence interval, 8.55-43.72]).

CONCLUSION

In our study population, intrapartum administration of magnesium sulfate was not found to be an independent risk factor for postpartum hemorrhage. Cesarean delivery was determined as an independent risk factor, consistent with previous reports.

Effective Dose of Prophylactic Oxytocin Infusion During Cesarean Delivery in 90% Population of Nonlaboring Patients With Preeclampsia Receiving Magnesium Sulfate Therapy and Normotensives: An Up-Down Sequential Allocation Dose-Response Study

BACKGROUND

Oxytocin administration during cesarean delivery is the first-line therapy for the prevention of uterine atony. Patients with preeclampsia may receive magnesium sulfate, a drug with known tocolytic effects, for seizure prophylaxis. However, no study has evaluated the minimum effective dose of oxytocin during cesarean delivery in women with preeclampsia.

METHODS

This study compared the effective dose in 90% population (ED90) of oxytocin infusion for achieving satisfactory uterine tone during cesarean delivery in nonlaboring patients with preeclampsia who were receiving magnesium sulfate treatment with a control group of normotensives who were not receiving magnesium sulfate. This prospective dual-arm dose-finding study was based on a 9:1 biased sequential allocation design. Oxytocin infusion was initiated at 13 IU/h, on clamping of the umbilical cord, in the first patient of each group. Uterine tone was graded as satisfactory or unsatisfactory by the obstetrician at 4 minutes after initiation of oxytocin infusion. The dose of oxytocin infusion for subsequent patients was decided according to the response exhibited by the previous patient in the group; it was increased by 2 IU/h after unsatisfactory response or decreased by 2 IU/h or maintained at the same level after satisfactory response, in a ratio of 1:9. Oxytocin-associated side effects were also evaluated. Dose-response data for the groups were evaluated using a log-logistic function and ED90 estimates were derived from fitted equations using the delta method.

RESULTS

The ED90 of oxytocin was significantly greater for the preeclampsia group (n = 27) than for the normotensive group (n = 40) (24.9 IU/h [95% confidence interval {CI}, 22.4-27.5] and 13.9 IU/h [95% CI, 12.4-15.5], respectively); the difference in dose requirement was 10.9 IU/h (95% CI, 7.9-14.0; P < .001). The number of patients with oxytocin-related hypotension, defined as a decrease in systolic blood pressure >20% from baseline or to <90 mm Hg, was significantly greater in the preeclampsia group (92.6% vs 62.5%; P = .030), while other side effects such as ST-T depression, nausea/vomiting, headache, and flushing, were not significantly different. There was no significant difference in the need for additional uterotonic or uterine massage, estimated blood loss, and need for re-exploration for uncontrolled bleeding.

CONCLUSIONS

Patients with preeclampsia receiving preoperative magnesium therapy need a greater intraoperative dose of oxytocin to achieve satisfactory contraction of the uterus after fetal delivery, as compared to normotensives.

Gestational and Hormonal Effects on Magnesium Sulfate's Ability to Inhibit Mouse Uterine Contractility

Magnesium sulfate is used as a tocolytic, but clinical efficacy has been seriously questioned. Our objective was to use controlled ex vivo conditions and known pregnancy stages, to investigate how 2 key factors, hormones and gestation, affect magnesium's tocolytic ability. We hypothesized that these factors could underlie the varying clinical findings around magnesium's efficacy. Myometrial strips were obtained from nonpregnant (n = 10), mid-pregnant (n = 12), and term-pregnant (n = 11) mouse uterus. The strips were mounted in organ baths superfused with oxygenated physiological saline at pH 7.4 and 37 °C. The effect of different concentrations of MgSO₄ (2-20 mM) was examined on spontaneous and oxytocin-induced (0.5-1 nM) contractions. Contractile properties (amplitude, frequency, and area under the curve) were measured before and after application of magnesium. Magnesium sulfate had a dose-dependent inhibitory effect on both spontaneous and oxytocin-induced contractions but was less effective in the presence of oxytocin. In spontaneous contractions, magnesium was more potent as gestation progressed (P < .0001). In the presence of oxytocin, however, there were no significant gestational differences in its effects on contraction. The rapid onset and reversal of magnesium's effects suggest an extracellular action on calcium entry. Taken together, we conclude that magnesium's actions are influenced by both gestational state and hormones, such that, at least in mice, it is least effective in early gestation with oxytocin present and most effective at term in the absence of oxytocin. That magnesium is least effective preterm and oxytocin decreases its effectiveness throughout gestation, may explain its disappointing clinical effects as a tocolytic.

Gestational and Hormonal Effects on Magnesium Sulfate's Ability to Inhibit Mouse Uterine Contractility

Magnesium sulfate is used as a tocolytic, but clinical efficacy has been seriously questioned. Our objective was to use controlled ex vivo conditions and known pregnancy stages, to investigate how 2 key factors, hormones and gestation, affect magnesium's tocolytic ability. We hypothesized that these factors could underlie the varying clinical findings around magnesium's efficacy. Myometrial strips were obtained from nonpregnant (n = 10), mid-pregnant (n = 12), and term-pregnant (n = 11) mouse uterus. The strips were mounted in organ baths superfused with oxygenated physiological saline at pH 7.4 and 37°C. The effect of different concentrations of MgSO4 (2-20 mM) was examined on spontaneous and oxytocin-induced (0.5-1 nM) contractions. Contractile properties (amplitude, frequency, and area under the curve) were measured before and after application of magnesium. Magnesium sulfate had a dose-dependent inhibitory effect on both spontaneous and oxytocin-induced contractions but was less effective in the presence of oxytocin. In spontaneous contractions, magnesium was more potent as gestation progressed ( P < .0001). In the presence of oxytocin, however, there were no significant gestational differences in its effects on contraction. The rapid onset and reversal of magnesium's effects suggest an extracellular action on calcium entry. Taken together, we conclude that magnesium's actions are influenced by both gestational state and hormones, such that, at least in mice, it is least effective in early gestation with oxytocin present and most effective at term in the absence of oxytocin. That magnesium is least effective preterm and oxytocin decreases its effectiveness throughout gestation, may explain its disappointing clinical effects as a tocolytic.

Associations of hypertensive disorders of pregnancy and outcomes of labor induction with prostaglandin vaginal inserts

OBJECTIVE

To evaluate the association between hypertensive (HTNsive) disorders of pregnancy and outcomes of labor induction, in two cohorts of women induced with either misoprostol vaginal insert (MVI) or dinoprostone vaginal insert (DVI).

STUDY DESIGN

This investigation was a post-hoc analysis of data from three Phase II and III, multi-center, double blind, randomized controlled trials of women induced with identical efficacy endpoints. A competing risk framework investigated the association between HTNsive disorders of pregnancy and the time-to-event endpoints of onset of active labor and vaginal delivery. We analyzed the overall incidence of the competing risk, cesarean delivery, by logistic regression to identify potential differences between the proportion of patients with cesarean and vaginal deliveries for each cohort.

RESULTS

401 women with HTNsive disorders during pregnancy underwent induction of labor in these studies (175 with DVI and 226 with MVI). Significant differences were noted in the cumulative incidence of vaginal delivery 24 hours following insertion between the non-HTNsive and HTNsive groups for both treatments, (57.1% vs. 47.4% (p=0.023) among MVI patients and 39.9% vs. 27.2% (p=0.017) among DVI patients). However, upon adjusting for potential confounders, the estimated relative rates of vaginal delivery among HTNsive vs. non-HTNsive patients was 0.947 (95% CI (0.637, 1.371), p=0.631) and 0.904 (95% CI (0.735, 1.113) p=0.341) within the MVI and DVI sub-groups respectively.

CONCLUSION

After adjustment for confounders, such as BMI, baseline modified Bishop score and gestational age, time-to-event outcomes for induction of labor using MVI or DVI in HTNsive women are not significantly different from non-HTNsive women.

Magnesium in obstetrics

Magnesium is a critical physiological ion, and magnesium deficiency might contribute to the development of pre-eclampsia, to impaired neonatal development and to metabolic problems extending into adult life. Pharmacologically, magnesium is a calcium antagonist with substantial vasodilator properties but without myocardial depression. Cardiac output usually increases following magnesium administration, compensating for the vasodilatation and minimising hypotension. Neurologically, the inhibition of calcium channels and antagonism of the N-methyl-d-aspartic acid (NMDA) receptor raises the possibility of neuronal protection, and magnesium administration to women with premature labour may decrease the incidence of cerebral palsy. It is the first-line anticonvulsant for the management of pre-eclampsia and eclampsia, and it should be administered to all patients with severe pre-eclampsia or eclampsia. Magnesium is a moderate tocolytic but the evidence for its effectiveness remains disputed. The side effects of magnesium therapy are generally mild but the major hazard of magnesium therapy is neuromuscular weakness.

Labor induction in preeclampsia: is misoprostol more effective than dinoprostone?

OBJECTIVE

To compare the efficacy of vaginal misoprostol versus dinoprostone for induction of labor (IOL) in patients with preeclampsia according to the WHO criteria.

STUDY DESIGN

Ninety-eight patients were retrospectively analyzed. A total of 47 patients received 3 mg dinoprostone suppositories every 6 h (max. 6 mg/24 h) whereas 51 patients in the misoprostol group received either 50 mug misoprostol vaginally every 12 h, or 25 mug every 6 h (max. 100 mug/24 h). Primary outcomes were vaginal delivery within 24 and 48 h, respectively.

RESULTS

The probability of delivering within 48 h was more than three-fold higher in the misoprostol than in the dinoprostone group: odds ratio (OR)=3.48; 95% confidence interval (CI) 1.24, 10.30, whereas no significant difference was observed within 24 h (P=0.34). No correlation was seen between a ripe cervix prior to IOL and delivery within 24/48 h (P=0.33 and P=1.0, respectively). More cesarean sections were performed in the dinoprostone group due to failed IOL (P=0.0009). No significant differences in adverse maternal outcome were observed between both study groups, whereas more neonates (12 vs. 6) of the dinoprostone group were admitted to the NICU (P=0.068).

CONCLUSION

This study suggests that misoprostol may have some advantages compared to dinoprostone, including improved efficacy and lower cost of the drug, even in cases of preeclampsia.

Does continuing oral magnesium supplementation until delivery affect labor and puerperium outcome?

OBJECTIVE

To determine the labor and puerperal impact of continuing oral magnesium supplementation until delivery.

STUDY DESIGN

Single-center study with matched controls. In 40 pairs of healthy women with vaginally delivered singleton pregnancies, matched for maternal age, race and parity, maternal and neonatal outcome endpoints were compared in those receiving continuous oral magnesium aspartate supplementation 15-30 mmol/d for at least 4 weeks until delivery (for constipation, calf cramps, preterm contraction without cervical effacement or additional tocolytics) versus non-supplemented controls.

RESULTS

In the magnesium group labor was nonsignificantly longer (stage 1: 326.0+/-187.5 min versus 276.7+/-140.8 min, P = 0.19; stage 2: 52.0+/-44.5 min versus 43.5+/-44.0 min, P = 0.40) and maximum oxytocin dose nonsignificantly higher (14.5+/-9.4 [median 12.0; n=15] versus 10.5+/-6.9 [median 7.5] mU/min, P = 0.28; n = 10). Fewer women had afterpains (12 versus 20, P=0.11), required spasmolysis (3 versus 14, P = 0.005), or could breastfeed their infants exclusively at discharge (24 versus 34, P = 0.04).

CONCLUSION

Continuing oral magnesium supplementation until delivery does not significantly prolong labor or increase the oxytocin requirement, but it significantly impairs breastfeeding competence.

Preeclampsia into eclampsia: toward a new paradigm

OBJECTIVE

This study was undertaken to characterize aspects of the natural history of eclampsia.

STUDY DESIGN

A retrospective analysis was performed on the records of patients with eclampsia who were delivered at two tertiary care hospitals.

RESULTS

Fifty-three pregnancies complicated by eclampsia were identified. Thirty-seven of the women were nulliparous. The mean age was 22 years (range, 15-38 years). Mean gestational age at the time of seizures was 34.2 weeks' gestation (range, 22-43 weeks' gestation). Twenty-eight women had antepartum seizures (53%); 23 of the 28 had seizures at home. Nineteen women had intrapartum seizures (36%). Eight of these women had seizures while receiving magnesium sulfate, and 7 had therapeutic magnesium levels. Six women had postpartum seizures (11%), 4 >24 hours after delivery. Headache preceded seizures in 34 cases. Visual disturbance preceded seizures in 16 cases. The uric acid level was elevated to >6 mg/dL in 43 women. There were no maternal deaths or permanent morbidities. There were 4 perinatal deaths. Two patients had intrauterine fetal deaths at 28 and 36 weeks' gestation. These mothers had seizures at home. One infant died of complications of prematurity at 22 weeks' gestation and one died of respiratory complications at 26 weeks' gestation. There were 4 cases of abruptio placentae, 1 of which resulted in fetal death. Of the 53 cases of eclampsia, only 9 were potentially preventable. One of these was that of a woman who was being observed at home. The other 8 women were hospitalized and had hypertension and proteinuria. Only 7 women could be considered to have severe preeclampsia before seizure (13%), and 4 of these 7 women were receiving magnesium sulfate.

CONCLUSIONS

Eclampsia was not found to be a progression from severe preeclampsia. In 32 of 53 cases (60%) seizures were the first signs of preeclampsia. In this series eclampsia appeared to be more of a subset of preeclampsia. Only 9 cases of eclampsia were potentially preventable with current standards of practice. Our paradigm for this disease, as well as our approach to seizure prophylaxis, should be reevaluated.