Association between raised serum relaxin levels during the eighteenth gestational week and very preterm delivery

OBJECTIVE: Our aim was to evaluate a possible association between serum relaxin levels in the 18th gestational week and preterm delivery. STUDY DESIGN: We conducted a nested case-control study that was based on serum samples obtained in the 18th week of gestation from 1545 unselected healthy primiparous women. Eleven case subjects were delivered very early (9 spontaneously, 2 by indicated cesarean delivery) and 42 moderately early (41 spontaneously, 1 by indicated cesarean delivery); 123 control subjects (121 having spontaneous labor, 2 undergoing indicated cesarean delivery) were randomly selected among the women with delivery at term. RESULTS: The serum relaxin concentration during the 18th gestational week was 63% higher among subjects with very preterm deliveries than among control subjects (P = .01, Mann-Whitney test). High relaxin levels during the 18th gestational week were associated with an increased risk of very preterm delivery (odds ratio, 11.3; 95% confidence interval, 2.14-59.1) and spontaneous very preterm delivery (odds ratio, 5.5; 95% confidence interval, 1.3-23). There was a negative correlation for case subjects and control subjects between serum relaxin concentrations during the 18th gestational week and gestational age at delivery (P < .05). CONCLUSION: Serum relaxin may be an independent predictor when identification of women at risk of very preterm delivery is attempted in the 18th gestational week.     

C-reactive protein in normal pregnancy

Maternal serum C-reactive protein (CRP) has been studied extensively as an adjunct in the diagnosis of subclinical infection among pregnant women with preterm labor or preterm rupture of membranes. However, before the utility of CRP can be studied in pregnancies with these complications, the effects of normal pregnancy and labor on maternal serum CRP levels must be established. We determined CRP levels serially from 22 weeks' gestation until delivery in healthy pregnant women without antepartum complications. Median CRP values for women not in labor ranged from 0.7-0.9 mg/dL, depending on gestational age; 95% of the values were 1.5 mg/dL or lower. No consistent change in CRP levels with gestational age was found among serially sampled women not in labor. The median CRP value for women in labor at term was 1.3 mg/dL, and 32% of values were over 1.5 mg/dL. Median CRP values in normal pregnancies appear to be higher than standardized values for nonpregnant individuals, and CRP values are further elevated in labor. Understanding the physiology and temporal course of the increase in CRP in normal pregnancy and labor may help to clarify the appropriate use of CRP in complicated pregnancies.     

Association between serum tumor necrosis factor-alpha and corticotropin-releasing hormone levels in women with preterm labor

AIM: To evaluate the association of serum corticotropin-releasing hormone (CRH) and tumor necrosis factor-alpha (TNF-alpha) in preterm labor. METHODS: Forty-nine primigravidas with a singleton viable pregnancy between 28 and 34 weeks of gestation were studied. They were divided into two groups. Group A consisted of 30 pregnant women (mean gestational age: 30.6 week) who presented with preterm labor and group B consisted of 19 pregnant women (mean gestational age: 29.8 week) with normal pregnancies. RESULTS: Women of group A had significantly higher serum CRH levels compared to those of group B (P < 0.01). Similarly, serum TNF-alpha levels were significantly higher in women of group A when compared to women of group B (7.8 +/- 3.72 pg/mL and 5.1 +/- 3.72 pg/mL, respectively). Furthermore, a positive correlation was found between serum CRH and TNF-alpha levels in both groups, which was stronger in women of group A. CONCLUSIONS: Our findings suggest that the increased levels of TNF-alpha and CRH found in pregnant women presenting with preterm labor may be involved in the pathophysiological mechanism of the latter. Furthermore, a positive interaction may exist between TNF-alpha and placental CRH, which may lead to enhanced production of the second and, therefore, facilitate the onset of labor.     

Maternal serum concentration of corticotropin releasing hormone (CRF) as a marker of preterm labor

There is still an urgent need for obstetricians to develop new, noninvasive, accurate methods of diagnosing preterm labor. The purpose of this study was to evaluation of maternal serum corticotropin-releasing factor concentrations and its concentration with onset of labor. The analysis was undertaken of women hospitalized in Research Institute Polish Mother's Memorial Hospital-Clinical of Perinatology (2001-2002) year with pregnancy between 16 to 35 weeks. All pregnancies were singleton gestation free of medical complications but with threatened labor. Maternal peripheral blood samples were obtained from antecubital vein during the first day of hospitalization. The control group consisted of 77 pregnant who delivered term infants whose growth was appropriate for gestational age. The study group consisted of pregnant women who gave preterm delivery. The serum CRF concentrations were measured using EIA method. Maternal serum CRF concentration in control group was 7.28 +/- 1.92 ng/ml. The material was obtained in 26.2 +/- 4.5 week of gestation. CRF concentration in studied group was 6.37 +/- 1.86 ng/ml +/- and the serum was obtained in 24.3 +/- 4.9 ng/ml weeks of gestation. The results were paradoxically significantly higher in control group. CONCLUSIONS: Our results were not in agreement with the findings of other investigators.     

Maternal complications of pregnancy increase beyond 40 weeks of gestation in low-risk women.

OBJECTIVE: We sought to determine when rates of maternal pregnancy complications increase for low-risk nulliparous and multiparous women at term. METHODS: We designed a retrospective cohort study of low-risk women delivered beyond 37 weeks gestational age from 1976 to 2001. Rates of mode of delivery and maternal complications of labor and delivery were examined by gestational age with both bivariate and multivariate analyses. Statistical significance was designated by P<0.05. RESULTS: We found that among the 32,828 low-risk women who delivered at 37 completed weeks and beyond, the rates of primary cesarean delivery, operative vaginal delivery, third- or fourth-degree perineal lacerations, and chorioamnionitis all increased at 40 weeks of gestation (P<0.001), and the rate of postpartum hemorrhage increased at 41 weeks of gestation (P<0.001). These increases of rates of complications were larger and increased at an earlier gestational age among nulliparous women. CONCLUSION: We found that the risk of maternal complications for otherwise low risk nulliparous and multiparous women increased as pregnancy progressed beyond 40 weeks of gestation. Counseling of women who progress past their EDC should include comparing the risks of induction of labor to that of expectant management.     

Placental sonolucency and pregnancy outcome in women with elevated second trimester serum alpha-fetoprotein levels.

BACKGROUND AND PURPOSE: Women with unexplained elevation of serum alpha-fetoprotein (AFP) are at increased risk for adverse pregnancy outcomes, including small for gestational age neonate, preterm labor, abruptio placentae, preeclampsia, intrauterine fetal death, and congenital malformations. This study investigated the association between placental sonolucency, elevation of maternal serum AFP, and pregnancy outcomes. METHODS: Singleton pregnancies (n = 168) with second trimester serum AFP level >/= 2.0 weight-adjusted multiples of the median (MoM) were recruited as the study group. Women with second trimester serum AFP level between 0.4 and 2.0 weight-adjusted MoM (n = 150) served as controls. A maternal Kleihauer-Betke stain was obtained for all participants. All participants were prospectively evaluated and the pregnancy complications were assessed by chart analysis after delivery. RESULTS: Compared with control subjects, women with placental sonolucent areas were not at increased risk for pregnancy complications, while women without sonolucent areas had higher risk of pregnancy complications. Singleton pregnancies with elevated serum AFP level had increased incidence of feto-maternal hemorrhage when placental sonolucency was observed. CONCLUSIONS: Our data suggest that feto-maternal hemorrhage may be the major factor contributing to elevated maternal serum AFP levels in pregnancies carrying placental sonolucencies. Screening for pregnancies with both elevated serum AFP and placental sonolucencies would help to identify the low-risk cases and facilitate cost-effective obstetric management.     

Level of perinatal care of the maternity unit and rate of cesarean in low-risk nulliparas

OBJECTIVE: To analyze the influence of level of perinatal care of the maternity unit on the rate of cesarean delivery during labor among women with low-risk pregnancies. METHODS: Using data from the PREMODA (PREsentation et MODe d'Accouchement: presentation and mode of delivery) study of 138 French maternity units, the delivery method in 3,654 low-risk nulliparas (live singleton fetus in cephalic presentation at term [37-41 weeks of gestation], born weighing 2,500-4,500 g, no uterine scar, no cesarean before labor, and no induction of labor for maternal or fetal disorders) was analyzed. Independent variables included maternal and fetal characteristics and the level of perinatal care of the maternity unit (level 1, 2a, 2b, and 3; where levels 2b and 3 routinely manage high-risk pregnancies). Univariable and multivariable analysis with a multilevel logistic model explored the factors associated with cesarean delivery during labor. RESULTS: Overall, the rate of cesarean during labor was 11.7%. The rate was significantly higher in level 2b (odds ratio 1.5, 95% confidence interval 1.1-2.1) and 3 (odds ratio 1.3, 95% confidence interval 1.0-1.9) maternity units than in level 1 facilities. The size and status of the facilities did not significantly affect these rates. Risk factors for cesarean were older maternal age, non-French origin, gestational age of 41 weeks, male sex, and high birth weight. CONCLUSION: Maternity units that frequently manage high-risk pregnancies (levels 2b and 3) have higher rates of cesareans during labor for their population of nulliparas at low risk than do facilities that deal mainly with low-risk pregnancies (level 1). LEVEL OF EVIDENCE: II-2.     

A randomized comparison of home uterine activity monitoring in the outpatient management of women treated for preterm labor

OBJECTIVE: The aim of the study was to evaluate home uterine activity monitoring as an intervention in reducing the rate of preterm birth among women treated for preterm labor. STUDY DESIGN: A total of 186 women were treated in the hospital with magnesium sulfate for preterm labor and were prospectively randomly assigned to study groups; among these, 162 were ultimately eligible for comparison. Eighty-two of these women were assigned to the monitored group and 80 were assigned to an unmonitored control group. Other than monitoring, all women received identical prenatal follow-up, including daily perinatal telephone contact and oral terbutaline therapy. Outcome comparisons were primarily directed toward evaluation of preterm birth at <35 weeks' gestation. Readmissions for recurrent preterm labor and observations lasting <24 hours were evaluated in monitored and unmonitored groups. Compliance with monitoring was also evaluated in the monitored group. RESULTS: The monitored and control groups were demographically similar. According to a multivariate logistic regression model, women with cervical dilatation of >/=2 cm were 4 times more likely to be delivered at <35 weeks' gestation (P <.05). Gestational ages at delivery were similar in the monitored and control groups. There was no significant difference in the overall rate of preterm delivery at <35 weeks' gestation between the monitored group (10.9%) and the control group (15.0%). The overall rates of delivery at <37 weeks' gestation were high (48.8% and 60.0% for monitored and control groups, respectively), and the difference was not significant. The numbers of women with >/=1 instance of readmission and treatment for recurrent preterm labor were equal in the monitored and control groups. The numbers of women with >/=1 hospital observation lasting <24 hours were not different between the groups. Compliance with monitoring did not significantly differ for women who were delivered at <35 weeks' gestation, women with >/=2 cm cervical dilatation at enrollment, or for African American women. CONCLUSION: A reduction in the likelihood of preterm delivery at <35 weeks' gestation was not further enhanced by the addition of home uterine monitoring to the outpatient management regimens of women treated for preterm labor.     

Maternal serum calponin 1 level as a biomarker for the short-term prediction of preterm birth in women with threatened preterm labor

Purpose: To assess the utility of maternal serum calponin 1 level in the prediction of delivery within 7 days among pregnancies complicated with threatened preterm labor.

Materials and methods: Eligible women who presented at 24–34 weeks of gestation with threatened preterm labor underwent sampling for serum calponin 1 level and cervical length measurement. They were followed up until delivery prospectively and the perinatal outcomes of the patients were recorded.

Results: Of 73 women included in the study, 36 women delivered within 7 days and 37 women delivered beyond 7 days after admission. The maternal serum calponin 1 level was significantly high in women who delivered within 7 days (p: 0.031). The threshold value of 2?ng/mL for maternal serum calponin 1 predicted delivery within 7 days with 61.1% sensitivity and 62.2 specificity (area under curve, 0.658, confidence interval 0.53–0.79). The general accuracy values for maternal cervical length measurement (≤25?mm), serum calponin 1 level (>2?ng/mL) and the combination of two tests to predict delivery within 7 days was found to be 64.4%, 61.6% and 72.1%, respectively.

Conclusions: The maternal serum calponin 1 level may be a useful biomarker in short-term prediction of preterm birth among pregnancies complicated with threatened preterm labor, in addition to cervical length measurement.     

Maternal serum free beta-hCG levels in uncomplicated pregnancies at the 10th-15th week of gestation and the development of obstetric complications

OBJECTIVE: To determine if free beta-human chorionic gonadotropin (hCG) serum levels at the 10th-14th week of gestation were different in groups of women who had experienced pregnancy complications. STUDY DESIGN: The obstetric records of women who had uncomplicated pregnancies when they consented to donate blood for biochemical research purposes early in pregnancy were reviewed. Two hundred thirteen of these women had donated blood at the 10th-14th week of gestation. Of these, 135 had uneventful pregnancies and delivered at term, 19 delivered before 37 weeks'gestation, 10 had fetuses small for gestational age, 4 developed pregnancy-induced hypertension, 7 developed gestational diabetes, 10 aborted spontaneously, 4 had an intrauterine fetal death after 20 weeks' gestation, and 24 were lost to follow-up. After the clinical groups had been identified, the 213 maternal serum stored samples were thawed and free beta-hCG measured by enzyme-linked immunosorbent assay. After normalization of the data, ANOVA was used to compare mean gestational age and mean free beta-hCG levels within groups. RESULTS: The overall mean gestational age at maternal blood sampling was 12.5 weeks. All groups had similar gestational ages at blood sampling (P = .18). The overall mean free beta-hCG serum level was 18.05 mIU/mL. Only the group of women who went on to experience spontaneous abortions had significantly lower free beta-hCG lev- els (mean, 10.45 mIU/mL; P < .03) CONCLUSION: Our data suggest that of the groups with obstetric complications evaluated, only the group of women who experienced spontaneous abortions had significantly different serum levels of free beta-hCG at the 10th-14th week of gestation.     

Cervical cerclage for prevention of preterm birth in women with twin pregnancy.

OBJECTIVE: To compare the effect of elective cervical cerclage in women with twin pregnancy on gestational age at time of delivery. METHOD: In a pragmatic fashion women in Abha Maternity Hospital, Saudi Arabia with twin gestations were allocated to receive either an elective cerclage (group I) or no cerclage (group II). Elective cerclage was performed at 12 to 14 weeks of gestation after sonographic examination of the fetus to confirm gestational age and exclude major congenital anomalies. In all cases, follow up of the pregnancy was continued until delivery. RESULTS: Of the 176 twin pregnancies included, cerclage was performed in 76 women, and no cerclage in 100 women. In Group I: 12 pregnancies ended in spontaneous miscarriage, 37 in preterm labor, and 27 women reached full term. There were a total of 106 live births in 62 women. In Group II: 8 women aborted, 44 women ended in preterm labor and 48 women reached full term. There were a total of 160 live births in 89 women. The gestational age at delivery ranged from 20 to 41 weeks. Multiple regression analysis did not show association between cerclage and time of delivery, although a trend was observed (P=0.056). CONCLUSION: Elective cerclage contributes little in prolongation of gestational age at the time of delivery in women with twin pregnancy, especially in women of high parity. Those with a previous history of preterm labor may be a subgroup that could benefit from elective cerclage.     

Is maternal serum relaxin associated with preterm delivery in Chinese pregnant women? A meta-analysis

Objective: A meta-analysis was performed to study the relationship between serum relaxin and preterm delivery in women with singleton pregnancies without estrogen stimulation.

Methods: Cohort and case-control studies were identified through searching databases (PubMed, Embase, Ovid, CBM, Wan fang, VIP, and CNKI). We carried out a continuous variable meta-analysis. The outcome was preterm delivery (gestation age <37 weeks).

Results: Fifteen studies were included, involving 1607 women with a singleton pregnancy. The pooled standard mean deviation (SMD) of 15 studies was 0.559 (95%CI: 0.002–1.196) and the heterogeneity was 96.6%. To reduce the heterogeneity, we chose random effects model and made subgroup analysis according to gestational age at sample testing (<18 weeks and ≥18 weeks) and race of included pregnant women. The pooled SMD of gestational age at sample testing ≥18 weeks and Chinese were 1.19 (95%CI: 0.63–1.75) and 1.61 (95%CI: 0.82–2.41) and the heterogeneity values (measured by I²) were 93.5% and 76.5%, respectively.

Conclusions: Elevated maternal serum relaxin of later than 18 weeks of gestational age is associated with singleton preterm birth in Chinese women. It might be an important information to prevent singleton preterm delivery in Chinese women. What’s already known about this topic? Previous reports reveal that there is a relationship between elevated maternal serum relaxin and preterm birth. However, the included articles contained twin pregnancies and estrogen stimulation, which obviously resulted in higher relaxin concentrations. What does this study add?     

Azurocidin levels in maternal serum in the first trimester can predict preterm prelabor rupture of membranes

Abstract

Objective: To determine the possible association between azurocidin in maternal serum in the first trimester of pregnancy and subsequent spontaneous preterm labor, preterm prelabor rupture of membranes, and iatrogenic preterm delivery.

Methods: Women who underwent first trimester screening for chromosomal abnormalities between January and November 2011 were included in the study, and a sample of maternal serum was obtained. In total, 1905 women were followed-up through the local record system, and 13 women with spontaneous preterm labor, 17 women with preterm prelabor rupture of membranes (PPROM), and 16 women with iatrogenic preterm delivery were identified. Twenty-two women with uncomplicated pregnancies who delivered at term were selected as controls. Maternal serum azurocidin levels in women were determined using ELISA.

Result: Women with PPROM had lower azurocidin levels (median 0.91?ng/mL, range 0.2–2.07) than women who delivered at term (median 1.63?ng/mL, range 0.4–10.98; p?=?0.02). No differences in azurocidin levels between women with labor at term and those with either spontaneous preterm labor (median 1.46?ng/mL, range 0.19–2.59; p?=?0.42) or iatrogenic preterm delivery (median 1.60?ng/mL, range 0.66–7.96; p?=?0.27) were found.

Conclusions: Low levels of azurocidin in maternal serum in the first trimester were associated with subsequent PPROM.     

Demographic and obstetric factors influencing pregnancy outcome in twin gestations

OBJECTIVE: Our purpose was to identify the influence of parity and previous preterm delivery on pregnancy outcome in twin gestations. STUDY DESIGN: A retrospective comparative analysis of women with twin gestations completing an outpatient preterm labor surveillance program between April 1995 and February 2000 was performed. Included were those enrolled at <24 weeks' gestation. Parity, maternal age, prepregnancy body mass index (BMI), cerclage, tocolytic use, and pregnancy outcome were identified. Data were divided into nulliparas, multiparas without previous preterm delivery, and those with previous preterm delivery. Analysis of variance and the Pearson chi2 test were used for statistical analysis. RESULTS: Data were analyzed for 1268 twin pregnancies. The mean gestational age at delivery for the multiparous women without a history of previous preterm delivery (35.3 +/- 2.7 weeks) was significantly greater than the mean gestational age at delivery for nulliparous (34.4 +/- 3.2 weeks) and multiparous women with a previous preterm delivery (34.0 +/- 3.1 weeks), P <.001. The greater gestational age at delivery in the multiparous women without a previous preterm delivery was associated with a significantly shorter newborn hospital stay and a lower need for mechanical ventilation use compared with the other groups (all P values < or =.001). CONCLUSION: In twin gestations, multiparous women without history of previous preterm delivery have a significantly greater gestational age at delivery, a lower incidence of cerclage, and a reduced neonatal hospital stay than do nulliparous women or those with a history of a previous preterm delivery.     

Total and ionized magnesium concentration in the blood plasma and erythrocytic magnesium concentration of women in the third trimester of pregnancy with imminent preterm labor

OBJECTIVES: There are some data concerning magnesium concentration influence on the risk of preterm labor. The estimation of magnesium concentration changes may be useful in prevention of preterm labor. DESIGN: Therefore the aim of our study was to find out the correlation between magnesium concentration and the risk of preterm labor. MATERIALS AND METHODS: Total magnesium concentration and ionized magnesium concentration in blood plasma and erythrocytic magnesium concentration ware examined in the three groups of: 23 women in the third trimester of pregnancy with imminent preterm labor under tocolytic therapy; 20 women in the third trimester of physiologic pregnancy and 19 non-pregnant healthy women in the reproductive age. RESULTS: We discovered statistically confirmed differences (p < 0,05 ) in ionized magnesium concentration as well between the group of women in physiologic pregnancy and non-pregnant women and between the group of pregnant women with imminent preterm labor and non-pregnant women. CONCLUSIONS: Although there were no statistically confirmed differences in total magnesium concentration and erythrocytic magnesium concentration between the three groups of examined women, there were statistically confirmed differences in ionized magnesium concentration between the pregnant and non-pregnant women. Our results suggest that ionized magnesium concentration is better indicator of magnesium balance in human's body than total magnesium concentration.     

Differing fetal growth patterns in pregnancies complicated by preterm labor

Previous studies have demonstrated diminished ultrasonic fetal growth parameters in women delivering preterm. In this study, we tested the following hypothesis: In pregnancies complicated by spontaneous preterm labor, 1) unsuccessful tocolysis is likely to be associated with diminished fetal growth, and 2) successful tocolysis is likely to occur when fetal growth is normal. Ultrasound examinations were performed in 78 pregnancies complicated by preterm labor before 35 weeks' gestation. Tocolysis was attempted unless contraindicated or unless cervical dilatation was advanced (4 cm or greater). Pregnancies delivering before 36 weeks' gestation were compared with those delivering after this gestational age. Among the 48 pregnancies delivered before 36 weeks' gestation, a significantly greater proportion had ultrasonic growth parameters lower than normal values at corresponding gestational ages. In contrast, those pregnancies that had successful tocolysis and delivered near term demonstrated a normal distribution of ultrasound growth parameters. In pregnancies complicated by preterm labor, ultrasonic documentation of diminished fetal growth may identify the subgroup at increased risk for preterm delivery.     

Total activin A in maternal blood as a marker of preterm delivery in low-risk asymptomatic patients

OBJECTIVES: To retrospectively evaluate whether increased serum levels of total activin A (t-activin A) are found in women who subsequently experience preterm delivery (PTD). METHODS: Data on maternal serum t-activin A concentrations were available from a total of 84 singleton pregnant women and included 14 PTD pregnancies, each matched for gestational age and length of freezer storage, with 5 control pregnancies having term delivery (TD). Analyte values were expressed as multiple(s) of the control median. RESULTS: The median t-activin A for controls and cases was 1.00 +/- 0.45 and 1.27 +/- 0.53 MoM, respectively. Univariate analysis of the MoM values was performed using the Kaplan-Meier algorithm. Differences in the rate of delivery using a t-activin A MoM cut-off of > or = 1 SD (equivalent to 1.26 MoM) were analysed using the log rank test. The cumulative rate of PTD (< 37 weeks) was significantly higher for women with t-activin A concentrations > or = 1.26 MoM than those with t-activin A concentrations below this cut-off (40% vs.. 10%, p-value = 0.0218 log rank test). CONCLUSIONS: T-activin A concentration is higher in women who will develop PTD in a low-risk population. T-activin A values are inversely proportional to the time elapsed from blood test to delivery. Prospective studies would determine the precise discriminability of this marker for PTD and the best week for performing the blood test, allowing for a proper calculation of the detection rate and a positive predictive value.     

Serial salivary estriol to detect an increased risk of preterm birth

OBJECTIVE: To evaluate serial measurements of salivary estriol (E3) to detect increased risk of spontaneous preterm labor and preterm birth. METHODS: A masked, prospective, multicenter trial of 956 women with singleton pregnancies was completed at eight United States medical centers. Saliva was collected weekly, beginning at the 22nd week of gestation until birth, and tested for unconjugated E3 by enzyme-linked immunosorbent assay. Women were separated into high-risk and low-risk groups using the Creasy scoring system. RESULTS: A single, positive (at or above 2.1 ng/mL) salivary E3 test predicted an increased risk of spontaneous preterm labor and delivery in the total population (relative risk [RR] 4.0, P <.005), in the low-risk population (RR 4.0, P < or =.05), and in the high-risk population (RR 3.4, P =.05). Two consecutive positive tests significantly increased the RR in all study groups, with a dramatic improvement in test specificity and positive predictive value but only a modest decrease in sensitivity. In women who presented with symptomatic preterm labor, salivary E3 identified 61% of those who delivered within 2 weeks, using a threshold of 1.4 ng/mL. CONCLUSION: Elevated salivary E3 is associated with increased risk of preterm birth in asymptomatic women and symptomatic women who present for evaluation of preterm labor.     

Effects of magnesium sulfate treatment on perinatal calcium metabolism. I. Maternal and fetal responses.

Serial maternal and cord blood determinations of the ions and hormones involved in calcium homeostasis were made in pre-eclamptic women treated with intravenous magnesium sulfate. A 4 gm loading dose followed by 1 to 2 gm/hr caused maternal serum magnesium concentrations to rise 150%, to levels of 3.3 to 4.5 mEq/L, and ionized calcium levels to fall 16%, to 1.89 mEq/L. The hypocalcemia etly altering calcitonin. Changes in total calcium paralleled those of ionized calcium; phosphorus levels were not affected by magnesium infusion. At the time of delivery the offspring of these women were hypermagnesemic and relatively hypocalcemic, although less so than their mothers. Fetal ionized calcium levels, although lower with magnesium treatment than in control subjects, were within the lower limits of the normal range, which perhaps explains why the fetus did not respond with increased PTH or decreased calcitonin output. These results indicate that the principal maternal response to magnesium-induced hypocalcemia involves increased parathyroid hormone secretion which tends to preserve maternal calcium homeostasis, while the fetus is partially protected from hypermagnesemia and hypocalcemia by the placenta.     

Serum magnesium levels in pregnancy and preterm labor

Pregnancy is marked by a state of hypomagnesemia. The serum magnesium level shows no gestational dependence (mean, 1.79 +/- 0.44 mg/dl) until 33 weeks, at which point it continuously declines. Serum magnesium is not depressed further with the onset of labor at term. Patients in preterm labor have a significantly depressed serum magnesium level (mean, 1.60 +/- 0.46 mg/dl; 21 to 33 weeks; p less than 0.0005). This level was not dependent on whether the etiology for the preterm labor was premature rupture of the membranes (PROM), twin gestation, abruption, placenta previa with bleeding, or chorioamnionitis. With PROM, the serum magnesium level was not depressed prior to the initiation of preterm labor. However, observation of hypomagnesemia for this and other etiologies just prior to the initiation of preterm labor were not available. Possible mechanisms by which hypomagnesemia induces uterine irritability are explored, including inhibition of adenyl cyclase with resultant increase in cytoplasmic calcium levels. Patients with diabetes mellitus appeared to have slightly reduced serum magnesium levels, but the results were not statistically significant. Magnesium levels in patients with preeclampsia were not significantly different from controls. Hypomagnesemia (magnesium 1.4 mg/dl or less) may be a marker for true preterm labor.