Beta-mimetics in preterm labour: an overview of the randomized controlled trials

Evidence for magnesium sulfate as a tocolytic agent

The objective of our study is to quantitatively examine the available evidence regarding the efficacy and side effects of magnesium sulfate for acute tocolysis (from randomized trials) compared with placebo and beta-agonist agents. Randomized trials comparing magnesium sulfate with placebo or beta-agonists for tocolysis were identified with a MEDLINE-based search and was supplemented by a search of obstetrical textbooks and bibliographies. Trials underwent quality evaluation and data abstraction by two independent, blinded investigators. Outcomes evaluated included delivery delay of various durations as well as the frequency of major and minor side effects. Summary odds ratios and 95 percent confidence intervals for dichotomous outcomes were calculated using a random effects model. Interstudy heterogeneity for these outcomes was assessed with a Q statistic. We identified 12 randomized controlled trials of magnesium sulfate for acute tocolysis. Four studies were excluded because of either lack of comparison of magnesium sulfate to either placebo or beta-agonists or lack of reporting clinical outcomes of interest. The eight remaining randomized trials comparing magnesium sulfate with placebo or beta-agonists were included in this analysis. There was no significant difference between MgSO4 and placebo for any of the measured outcomes for delay in delivery. Comparing magnesium sulfate to ritodrine or beta-agonists did not demonstrate any differences between the agents in achieving clinically significant tocolysis. There was a significant difference between MgSO4 and beta-agonists in the frequency of medication discontinuation because of side effects, but not in the frequency of major adverse drug events. There are few data comparing magnesium sulfate with a placebo for acute tocolysis. Magnesium sulfate seems to be comparable to ritodrine and beta-agonists, although the available data are not sufficient for a rational choice between these agents.

Successful magnesium sulfate tocolysis: is "weaning" the drug necessary?

OBJECTIVE

Magnesium sulfate is the most commonly used tocolytic agent for preterm labor. A common clinical practice is to slowly discontinue the drug (wean) after successful tocolysis. Our objective was to determine the necessity of this practice.

STUDY DESIGN

A prospective, randomized clinical trial was performed from June 1993 to July 1996. After successful magnesium sulfate tocolysis, patients with preterm labor were randomized to two groups: stopping the drug abruptly (no weaning) or gradually weaning the drug (approximately 1 gm every 4 hours). Preterm labor was defined as documented cervical change with regular uterine contractions or regular uterine contractions with a cervix of 2 cm and 75% effacement. The primary outcome variable was the necessity to reinstitute magnesium sulfate therapy within 24 hours of discontinuation of successful tocolysis.

RESULTS

One hundred forty-one patients completed the study. No patient in the no-wean group required retocolysis within 24 hours of magnesium discontinuation. However, eight patients in the wean group required retocolysis within 24 hours of magnesium discontinuation (p = 0.01). Significantly more patients in the wean group had retocolysis during pregnancy (3 vs 12, p = 0.03). Patients in the wean group were also in the labor and delivery unit longer and, as would be anticipated, received magnesium sulfate significantly longer. No differences in the neonatal outcomes were noted between the two groups. Seventy-seven percent of the patients in the study were delivered prematurely.

CONCLUSION

This study demonstrated an increased need for retocolysis in the group weaned from magnesium sulfate. We also found that patients in the wean group had an increased labor and delivery time and a longer administration time of magnesium sulfate. Thus weaning magnesium sulfate increases health care cost. The practice of weaning magnesium sulfate does not appear beneficial.

Expression of beta-adrenergic receptor kinase subtypes in the pregnant rat myometrium

OBJECTIVE

This study tested the hypothesis that the increase in uterine tachyphylaxis to beta-adrenergic stimulation during pregnancy is associated with increased expression of the beta-adrenergic receptor-inactivating protein kinases.

STUDY DESIGN

Messenger ribonucleic acid was isolated from snap-frozen myometrium collected from nonpregnant and pregnant rats ranging from 10 to 22 days of gestation. Autoradiographic analysis of beta-adrenergic receptor-inactivating protein kinase messenger ribonucleic acid expression was performed after hybridization with specific complementary deoxyribonucleic acid probes for types 1 and 2 beta-adrenergic receptor-inactivating protein kinases. Probe-specific hybridization was normalized for ribosomal ribonucleic acid detected with methylene blue. Protein expression was detected by Western analysis with use of specific polyclonal antibodies.

RESULTS

Myometrial beta-adrenergic receptor-inactivating protein kinase type 2 messenger ribonucleic acid and protein levels increased during the course of pregnancy and in postpartum day 1. In contrast, type 1 levels remained unchanged during the same period. Estrogen treatment resulted in a modest 20% decrease in messenger ribonucleic acid levels of both subtypes. This effect was reversed with progesterone treatment.

CONCLUSION

These results suggest that the myometrium undergoes a functional remodeling late in pregnancy to a state promoting myometrial contractions. The increased myometrial expression of type 2 beta-adrenergic receptor-inactivating kinase may explain the decreased effectiveness of beta 2-adrenergic receptor-mediated contraction inhibition at the end of pregnancy and labor.

Rapid fetal fibronectin swab-test in preterm labor patients treated by betamimetics

OBJECTIVE

A preliminary study to examine the value of a rapid fetal fibronectin swab-test used as a bedside test in the prognosis of preterm labor.

STUDY DESIGN

Women presenting with preterm labor and intact membranes and less than 3 cm dilated were enrolled in a single referral center. Cervicovaginal swabs were assessed for the presence or absence of fetal fibronectin by means of a rapid monoclonal antibody assay the positivity of which was revealed by a colorimetric reaction. Results were compared with uterine contractions frequency, Bishop cervical score, duration of tocolysis and interval to delivery. The predictive value of fetal fibronectin test for delivery within 7, 14 or 21 days from sampling and before 32 and 37 weeks' of gestation was assessed in the two groups.

RESULTS

Among 124 eligible patients, 19 presented with a positive fibronectin test and 105 with a negative one. Gestational age at sampling, Bishop cervical score and duration of tocolysis were identical in the two groups. The number of contractions was significantly lower and gestational age at delivery was significantly higher in the fibronectin negative group. Fetal fibronectin in cervicovaginal secretions has a high sensitivity (89%) for delivery within 7 days. Absence of fetal fibronectin in cervicovaginal secretions of patients presenting with uterine contractions could rule out preterm labor within 7 and 14 days with a predictive value of 99 and 95.2%, respectively. In negative fetal fibronectin patients, preterm delivery before 32 and 37 weeks' is unlikely to occur with a predictive value of 97 and 85%, respectively.

CONCLUSION

Cervicovaginal fetal fibronectin detected by a rapid bedside swab-test in women with symptoms of preterm labor compares favourably with quantitative assays and could prove useful in the management of preterm labor. This should be confirmed in a longer prospective study.

On the mechanism of action of ethodin in inducing myometrium contractions

1. Ethodin (Rivanol, 6,9-diamino-2-oxyethyl acridine lactate), has been described as an effective drug to induce uterine contractions similar to those in a physiologic labor in still-birth with uterine inertia. We investigate the mechanisms involved in the effect of this compound in contracting the smooth-muscle cells of the myometrium to improve our understanding of the processes involved in the onset of labor. 2. We conclude that the contractile effect of ethodin is mediated through the activation of uterine mast cells that release mediators able to contract the myometrium.

Preterm labor and preterm premature rupture of the membranes. Diagnosis and management

Preterm delivery due to preterm labor and pPROM is responsible for most infant morbidity and mortality in the United States. The patient who presents with suspicious symptoms should undergo a thorough evaluation to confirm the diagnosis of either entity and identify a treatable cause. Determination of gestational age, fetal well-being, and the presence of intrauterine infection is a crucial step in subsequent management. Corticosteroid therapy has been demonstrated to be one of the most effective antenatal interventions to reduce infant morbidity and should be administered to patients with preterm labor, if feasible, when fetal pulmonary maturity is absent or undocumented. We recommend a similar protocol regarding gravidas with pPROM remote from term but recognize the need for further study in this area. Acute tocolytic therapy has been demonstrated to offer short-term benefit to enhance corticosteroid effect. However, all of the available tocolytic agents carry significant risks to the mother and fetus. As such, administration of these agents should be given only when the potential benefits outweigh the risks of administration. Evaluation for fetal pulmonary maturity and intrauterine infection, in concert with evaluation of gestational age-dependent risks of prematurity, may be helpful in determining whether tocolysis should be attempted. Adjunctive antibiotic administration has not been shown to reduce maternal or infant morbidity in the face of preterm labor. However, such treatment offers a reduction of chorioamnionitis, prolongation of latency, and a possible reduction of neonatal infectious and gestational age-dependent morbidity in the setting of pPROM remote from term. Finally, current guidelines recommend the administration of intrapartum GBS prophylaxis when preterm birth or prolonged membrane rupture is anticipated if GBS carrier status is unknown or positive. Intrapartum treatment with intravenous penicillin or ampicillin is appropriate.

Fetal drug therapy

As prenatal diagnosis has become more sophisticated, avenues for a variety of intrauterine therapies have been opened. Considerable experience has been gained with surgical and pharmacologic approaches. This article provides a review of intrauterine drug therapy aimed at preventing fetal and neonatal disease and treating existing fetal conditions. The future awaits the exciting applications of intrauterine hematopoietic transplants and genetic therapy.

Effect of chronic tocolytic therapy on maternal ventricular function in pregnant rabbits

OBJECTIVE

Our purpose was to determine whether peripartum cardiomyopathy may be associated with chronic beta-mimetic tocolytic therapy.

STUDY DESIGN

On gestational day 20 (term 31 days), two 200 microliter Alzet miniosmotic pumps were implanted in the subcutaneous tissue of pregnant New Zealand White rabbits. Each pump was filled with terbutaline (20 micrograms/microliter, n = 7) or saline solution (0.9%, n = 7) and infused continuously for 7 days. The rabbits were killed on the twenty-eighth gestational day. Maternal hearts were placed on a Langendorff (nonejecting) perfusion apparatus for assessment of cardiac function. At a constant perfusion pressure and heart rate left ventricular diastolic pressure was varied while left ventricular developed pressure and left ventricular +/- rate of pressure rise, index values of left ventricular contractility and relaxation, were continuously recorded. Comparisons between groups at each preload were made by analysis of variance.

RESULTS

Hearts taken from terbutaline-treated rabbits exhibited periodic arrhythmias and mechanical alternans in five of seven hearts versus one of seven in the saline solution group. At a preload of 0 mm Hg both left ventricular developed pressure (88.0 vs 48.4 mm Hg, p < 0.001) and left ventricular rate of pressure rise (1406 vs 653 mm Hg/sec, p < 0.001) were less in terbutaline-treated rabbits. At a preload of 10 mm Hg left ventricular developed pressure (104.4 vs 56.7 mm Hg, p < 0.01) and rate of pressure rise (1424 vs 694 mm Hg/sec, p < 0.001) were also significantly less in terbutaline-treated rabbits. Left ventricular relaxation was also impaired at all preloads.

CONCLUSIONS

In this model chronic administration of terbutaline during late pregnancy significantly depresses global maternal cardiac function.

Preterm labour and delivery

Preterm birth is a major cause of perinatal morbidity and mortality. It accounts for 5-10% of all births, and any treatment to prevent it could have a profound effect on neonatal outcome in both human and economic terms. The pathogenesis of both term and preterm birth remain poorly understood. Our ability to predict those at risk of preterm labour is also inaccurate, despite the creation of scoring systems, uterine activity monitoring, cervical ultrasound and several biochemical markers. Current drug therapies for preterm labour have not been shown in randomised controlled trials to significantly affect perinatal morbidity and mortality. Furthermore, most are associated with significant maternal or fetal side effects. Nitric oxide (NO) is a potent smooth muscle relaxant, produced when NO synthase acts on the amino acid L-arginine. Its presence has been demonstrated in human myometrium. We have conducted an observational study which has suggested that glyceryl trinitrate (GTN), and NO donor, may be effective in prolonging gestation. A randomised trial comparing GTN to intravenous ritodrine is currently recruiting patients; results will be available in the Spring of 1997. Few side effects have so far been encountered. Evidence suggests that GTN, an NO donor, should be a safe and effective tocolytic and early observations are encouraging; randomised trials currently underway should determine the significance of this breakthrough in the management of preterm labour.

Urinary trypsin inhibitor: a new drug to treat preterm labor: a comparative study with ritodrine

Prevention of preterm delivery is one of the difficult problems facing obstetricians. beta Adrenergic agonists, especially ritodrine, are commonly used in these cases.

OBJECTIVES

The aim of this research was to study and compare the effect of urinary trypsin inhibitor (UTI) which has anti-inflammatory anti-cytokine effects with ritodrine in treating preterm labor.

STUDY DESIGN

Patients in preterm delivery were randomly selected to be treated either by ritodrine or UTI. In the ritodrine group, uterine contractions were initially suppressed by high doses of ritodrine (up to 300 micrograms/min) and then a maintenance dose was given until 35 weeks of gestation. In the UTI group one vaginal suppository (5000 U) was used daily for 2 weeks. Patients with recurrent preterm uterine contraction during the initial 14 days of treatment, who needed course of other drugs to suppress the contractions, were excluded from the study. Patients responding to the drugs were followed until delivery. Tocolytic index and elastase concentration in the cervical mucus was calculated. Recurrence rate of uterine contraction and time of elongation of pregnancy since the beginning of treatment was calculated.

RESULTS

UTI was more effective than ritodrine in inhibition of recurrent uterine contraction and elongation of pregnancy. No side effects could be observed after treatment with UTI for the mother or the fetus.

CONCLUSION

UTI may be a new therapeutic method for the inhibition of preterm delivery through suppression of cytokines and inflammatory mediators.

Randomised comparison between a loading and incremental dose model for ritodrine administration in preterm labour

OBJECTIVE

To compare a new loading dose regimen for intravenous ritodrine administration in preterm labour with the conventional dose regimen.

DESIGN

Multicentre randomised trial using numbered opaque sealed envelopes.

SETTING

Five teaching hospitals in the Netherlands.

PARTICIPANTS

Women (n = 203) in preterm labour at less than 34 weeks of gestation.

INTERVENTIONS

Women received either a loading dose ritodrine infusion followed, as soon as tocolysis was reached, by a decrease in infusion rate or the conventional schedule of increasing doses until uterine quiescence was achieved.

RESULTS

Frequency of successful tocolysis (71%) and duration of treatment (55 h) were similar in both groups, but the loading dose schedule was better tolerated with fewer adverse events. Also the number of dose adjustments was smaller than in the incremental dose group (P < 0.001). Overall, the differences between the two regimens were unexpectedly small.

CONCLUSIONS

Despite the small differences, the loading model is easier to apply, requires fewer dose adjustments, is better tolerated with less side effects, and reduces the likelihood of clinical error.

Double-blind evaluation of ritodrine sustained release for oral maintenance of tocolysis after active preterm labour

OBJECTIVE

To evaluate the effect of ritodrine sustained release capsules for maintaining uterine quiescence after successful treatment of active preterm labour.

DESIGN

Multicentre placebo-controlled trial.

SETTING

Five teaching hospitals in the Netherlands.

PARTICIPANTS

Women (n = 95) at less than 35 weeks of gestation in whom active preterm labour had been stopped with intravenous ritodrine.

INTERVENTIONS

Women received either two 40 mg ritodrine sustained release capsules (n = 50) or identical placebo capsules (n = 45) three times a day for seven days.

RESULTS

The proportion of women who received another course of active treatment was significantly smaller with the sustained release than with placebo (1 of 50 versus 11 of 45: P = 0.003) as was the number delivering because of preterm labour during treatment (0 of 50 versus 4 of 45: P = 0.04). There were no other significant differences between the two groups.

CONCLUSIONS

Maintenance treatment with ritodrine sustained release capsules after arrest of preterm labour reduces the risk of recurrences of preterm labour that necessitate treatment or precipitate delivery.

Contraction inhibition by beta-agonists progressively decreases before labor in the rat myometrium

OBJECTIVE

This study tested the hypothesis that gestational age and agonist concentration are important determinants of beta-adrenergic-dependent myometrial contraction inhibition.

STUDY DESIGN

In vitro concentration-response curves for ritodrine and terbutaline were generated with myometrial strips collected from 21-day-pregnant rats. The in vitro efficacy of ritodrine (0.1 mumol/L) was evaluated in tissue from 15-, 18-, and 21-day animals. Contractile responses were analyzed by computer and normalized to a control potassium response.

RESULTS

The degree of the inhibitory effects of both drugs was concentration dependent over the range of 0.01 to 10 mumol/L. The duration of contraction inhibition progressively decreased from 15 to 21 days of pregnancy.

CONCLUSION

The degree of tachyphylaxis with beta-agonists is dependent on and increases with the gestational age of the target tissue. beta-Agonist type was not an important determinant of the duration of inhibitory response. We speculate that the effect of gestational age on tachyphylaxis may be related to increased myometrial expression of inactivating beta-adrenergic receptor kinases.

Incidence of adverse cardiopulmonary effects with low-dose continuous terbutaline infusion

OBJECTIVE

Our purpose was to determine the incidence of adverse cardiovascular effects of terbutaline sulfate when administered as a continuous subcutaneous infusion in women with arrested preterm labor.

STUDY DESIGN

Over a 6-year period records from 8709 women prescribed this therapy for preterm labor that had previously been arrested with other intravenous tocolytics were reviewed. These women were assessed daily for cardiovascular complaints and tolerance of the medication, while either in the hospital or at the home (by telephone). The main outcomes studied were the occurrence of pulmonary edema, sustained cardiac arrhythmias, chest pain, or myocardial ischemia. Any maternal death regardless of cause was also reviewed.

RESULTS

Of the 8709 subjects, 47 (0.54%) had one or more cardiopulmonary problems. Pulmonary edema developed in 28 patients (0.32%) while receiving continuous subcutaneous infusion of terbutaline, 5 at home and 23 in the hospital. Of the total, 17 women were being treated concurrently with large amounts of intravenous fluids and one to three other tocolytic agents. In the 11 remaining subjects, 4 were diagnosed with pregnancy-induced hypertension and/or multiple gestation. Nineteen patients experienced other adverse cardiovascular effects, including electrocardiogram changes, irregular heart rate, chest pain, or shortness of breath.

CONCLUSIONS

Continuous terbutaline infusion for women with stabilized preterm labor is associated with much fewer adverse effects than previous literature regarding intravenous beta-adrenergic agonist therapy would suggest.

New perspectives for the effective treatment of preterm labor

Preterm birth (before 37 completed weeks of gestation) continues to account for the vast majority of neonatal morbidity and mortality. The incidence of preterm birth can be reduced by appropriate social interventions and antenatal care. Currently available tocolytic agents suffer from low uterospecificity and prolong pregnancy only marginally, although postponement of birth by a few days may be of some value. Further progress is needed in at least four areas: prevention of preterm labor; identification of preterm labor; selection of candidates for tocolysis, and treatment of preterm labor. Effective, early treatment of vaginosis offers particular promise for the prevention of preterm labor and identification of specific biochemical markers will facilitate early detection of this process. Oxytocin antagonists offer greater specificity than current tocolytics and can be expected to show improved efficacy and risk profiles. Such compounds will allow more effective treatment of preterm labor with a lower risk of side effects.

Fetal fibronectin improves the accuracy of diagnosis of preterm labor

OBJECTIVE

Our purpose was to assess the utility of cervicovaginal expression of fetal fibronectin in the diagnosis of preterm labor.

STUDY DESIGN

Women seen between 24 and 34 weeks' gestation with symptoms of preterm labor, intact membranes, and cervical dilatation < 3 cm were enrolled at five university medical centers. Cervicovaginal swabs were obtained and assayed for the presence of fetal fibronectin by means of a monoclonal antibody assay. Results were compared with cervical dilatation and uterine contraction frequency as indicators of interval to delivery and delivery before 37 weeks.

RESULTS

A total of 192 eligible women at a mean gestational age of 30.8 +/- 2.9 weeks were enrolled from a population of 418 subjects screened. The rate of preterm birth was 32.3% (62/192). The mean interval from presentation to delivery was 25.3 +/- 24.1 days in the 45 subjects with a positive fibronectin assay and 52.4 +/- 24.8 days in the 147 subjects with a negative assay (p = 0.0001). The sensitivity, specificity, and positive and negative predictive values of fetal fibronectin expression for delivery < 37 weeks were 44% (27/62), 86% (112/130), 60% (27/45), and 76% (112/147). The fetal fibronectin assay was especially useful in predicting risk of delivery within 7 days (sensitivity 93% [13/14], specificity 82% [146/178], positive predictive value 29% [13/45], and negative predictive value 99% [146/147]) and was notably superior to both cervical dilatation > 1 cm and contraction frequency greater than or equal to eight per hour (sensitivities 29% and 42%, specificities 82% and 67%, positive predictive values 11% and 9%, and negative predictive values 94% and 94%, respectively.

CONCLUSION

Cervicovaginal fetal fibronectin predicts delivery within 7 days more accurately than do cervical dilatation and contraction frequency in a population of women evaluated for early preterm labor.

Update on tocolytic therapy

OBJECTIVE

To review medications currently being used or investigated for the treatment of preterm labor. Adverse effects, pharmacoeconomic issues, and therapeutic controversies are included.

DATA SOURCES

A MEDLINE search, limited to English-language articles and publication years of 1989-1994, was used to identify pertinent literature. Additional references were identified from articles retrieved in the search.

STUDY SELECTION

Studies were chosen on drugs that are available or whose approval is anticipated in the US: ritodrine, terbutaline, hexoprenaline, and magnesium sulfate. Several studies comparing indomethacin and nifedipine with currently used medications are also included. Oxytocin antagonists, now in Phase II clinical trials, are discussed. Studies focusing on adverse reactions were included because of serious concerns that these reactions raise.

DATA EXTRACTION

Part of the controversy surrounding tocolytic agents involves the difficulty in comparing data from different trials, particularly because the criteria for diagnosis of preterm labor vary significantly. Therefore, no attempt was made to directly compare data from different sources; individual study data are presented.

DATA SYNTHESIS

Most studies reviewed using the beta-agonists showed each to be comparable in effectiveness when given parenterally during early preterm labor. These drugs usually delay delivery for 24-48 hours. There is less evidence that they are consistently effective in the long-term treatment of preterm labor. The adverse effects vary somewhat, but all beta-agonists have been reported to cause pulmonary edema, which is the most serious adverse effect associated with the use of these medications to inhibit labor. Indomethacin and nifedipine may be alternative choices for tocolytic therapy, but each has different adverse reactions that also make them less than ideal agents. Oxytocin antagonists may provide more specific therapy and are currently being investigated.

CONCLUSIONS

The beta-agonists are effective in delaying delivery for 24-48 hours in most patients; however, there are potential risks involved. Magnesium sulfate, prostaglandin synthetase inhibitors, calcium-channel blockers, and oxytocin antagonists may provide alternative choices for the treatment of preterm labor associated with neonatal morbidity and mortality. Each of the medications has advantages and disadvantages at different stages of gestation.

Fetal fibronectin detection for prediction of preterm birth in low risk women

OBJECTIVE

To evaluate the clinical value of cervical fetal fibronectin detection by a quantitative enzyme-linked immunosorbent assay (ELISA) (PTDcheck, Adeza Biomedical, Sunnyvale, California, USA) as a screening tool for the prediction of preterm contractions and preterm delivery in an unselected population of pregnant women globally considered to be at low risk for preterm delivery (n = 133).

DESIGN

A prospective study in which cervical fetal fibronectin samples were collected at two-week intervals between 26 and 36 weeks of gestation.

SETTING

A regional training hospital.

SUBJECTS

One hundred and thirty-three singleton pregnancies presenting consecutively at an antenatal clinic.

MAIN OUTCOME MEASURE

Occurrence of preterm contractions and preterm delivery (delivery at < 37 weeks of gestation).

RESULTS

Twenty-four (18%) patients were considered positive for the presence of fetal fibronectin. Overall 15 patients (11%) developed preterm contractions and, despite therapeutic intervention, 10 patients (8%) were delivered preterm. As a predictor for preterm contractions, cervical fetal fibronectin detection had a sensitivity of 47%, a specificity of 86%, a positive predictive value of 29% and a negative predictive value of 93%. As a predictor for preterm delivery, cervical fetal fibronectin detection had a sensitivity of 60%, a specificity of 85% a positive predictive value of 25% and a negative predictive value of 96%.

CONCLUSIONS

Cervical fetal fibronectin determinations at a two-week sampling frequency for prediction of preterm birth in a general obstetric population at low risk for preterm birth has limited clinical value as a routinely performed screening procedure.

Dexamethasone partially protects the myometrium against beta-adrenergic agonist-induced desensitization in vivo in the rat

OBJECTIVE

Our purpose was to determine the ability of dexamethasone to prevent the onset of myometrial desensitization to beta-adrenergic agonists in vivo.

STUDY DESIGN

On day 5 post partum chronically catheterized rats were randomized to receive either dexamethasone or corn oil (vehicle), followed 12 hours later by a continuous infusion of either isoproterenol or saline solution (vehicle). Uterine contractions were monitored throughout. We measured myometrial glucocorticoid receptor levels in chronically catheterized and sham-operated rats and beta 2-adrenergic receptor densities in the experimental rats before and during the infusions.

RESULTS

Surgery did not lead to any decrease in glucocorticoid receptor number. Dexamethasone significantly increased the duration of myometrial responsiveness to isoproterenol compared with vehicle-pretreated rats, although agonist-induced down-regulation of beta-adrenergic receptor number was not prevented.

CONCLUSION

Dexamethasone partially protects the rat myometrium from desensitization induced by the continuous infusion of beta-adrenergic agonists through mechanisms independent of the beta 2-receptor.

A prospective randomized clinical trial comparing a new oral sustained-release ritodrine with conventional tablets

OBJECTIVES

Evaluation of maternal metabolic and cardiovascular responses to treatment with the new sustained-release oral ritodrine as compared with the conventional tablets.

METHOD

Thirty-two pregnant patients who had successful intravenous tocolysis were randomly assigned to treatment with either ritodrine tablets or sustained-release capsules. After 5 days of the randomly determined first oral treatment each patient was shifted to the alternate ritodrine formulation for a further 5-day course. Each patient underwent metabolic and non-invasive hemodynamic evaluation.

RESULTS

Echocardiographic parameters during treatment with ritodrine tablets were not significantly different from during sustained-release capsules. Mean systolic blood pressure increased significantly during peak drug activity in patients treated with ritodrine tablets and not during treatment with the sustained-release form. Fasting plasma glucose levels were higher in patients on conventional tablets therapy than in patients on sustained-release ritodrine therapy (88.9 +/- 9 mg/dl vs. 78.7 +/- 8 mg/dl, P < 0.05) while levels following a 50-g oral glucose challenge test did not differ significantly (135 +/- 32 mg/dl vs. 124.5 +/- 27 mg/dl)

CONCLUSIONS

Because of fewer metabolic and cardiovascular side-effects, the new oral therapy offers some advantages over the presently available tablets.

Eradication of Viridans streptococci from the amniotic cavity with transplacental antibiotic treatment

We report a case of eradication of Viridans streptococci from the amniotic cavity in a patient with preterm labor and intact membranes by transplacental antibiotic treatment. Following this modality of treatment, preterm labor was arrested and the pregnancy continued uneventfully until normal term delivery. We suggest that transplacental antibiotic treatment should be seriously considered as part of the medical armamentarium for treatment of patients with preterm labor and microbial invasion of the amniotic cavity.

The epidemiology of neonatal respiratory disease

The epidemiology of many conditions affecting the newborn infant is influenced by the health of the mother, prematurity and the effects of medical and obstetric management. In this review we have considered the role of each of these factors in seven respiratory conditions presenting in the newborn infant.

A loading model for ritodrine administration in preterm labour

OBJECTIVE

To develop a ritodrine infusion scheme for preterm labour that avoids plasma levels above those needed for tocolysis, requires only one rate adjustment, and is easy to apply in practice.

DESIGN

Prospective study of tocolytic effect and plasma ritodrine concentrations during application of the infusion scheme.

SETTING

High risk labour ward.

SUBJECTS

Consecutive series of 31 women in labour at less than 36 weeks' gestation.

INTERVENTION

Loading dose ritodrine infusion followed, as soon as tocolysis is reached, by a decrease in the infusion rate calculated on the basis of the interval between start of treatment and tocolysis.

RESULTS

Overall, steady state ritodrine levels were nearly identical to those at the time of tocolysis and correlated well with levels anticipated on the basis of our calculation (n = 30; r = 0.91; P < 0.001). Adjustments during steady state were made in 12 women (40%), but in only two of them within 12 h after tocolysis had been reached. Delivery was postponed for more than 48 h in 29 women (93.5%) and beyond 37 weeks' gestation in 19 (61.3%).

CONCLUSION

The loading model is easy to apply, avoids relative overdoses, requires few adjustments, is well tolerated, uses smaller quantities of ritodrine, and results in lower plasma ritodrine concentrations than the conventional infusion scheme.

Acute tocolysis for fetal distress: terbutaline versus magnesium sulphate

Forty-six women in active labour who developed fetal distress requiring abdominal delivery were randomized to receive 0.25 mg of terbutaline (subcutaneously) or magnesium sulphate as a 4-g bolus (intravenously) to decrease uterine activity. The terbutaline-treated group in contrast to the magnesium sulphate-treated group had reduced uterine activity as measured by Montevideo units (p < 0.002). This decrease in uterine activity was noted more rapidly in all 23 patients who received terbutaline, 1.8 +/- 0.74 minutes compared to 7.5 +/- 2.1 minutes in the 16 of 23 patients (magnesium sulphate-treated women) in whom a decrease in uterine activity occurred (p < 0.001). Umbilical cord arterial blood pH at delivery was less than 7.20 in only 2 of the 23 patients treated with terbutaline versus 7 of the 23 in the magnesium sulphate-treated group. We conclude that terbutaline is an effective and more rapid-acting tocolytic agent to arrest uterine activity prior to delivery for fetal distress.

Currently recommended oral regimens for ritodrine tocolysis result in extremely low plasma levels

OBJECTIVE

Our aim was to compare plasma drug levels in patients receiving ritodrine intravenously with those in patients receiving ritodrine orally at recommended dosages.

STUDY DESIGN

Plasma samples from 20 pregnant patients treated with intravenous ritodrine (50 to 300 micrograms/min), 9 patients treated with oral ritodrine only (60 to 120 mg per 24 hours), and 9 patients treated first with intravenous and subsequently with oral ritodrine were analyzed for ritodrine concentration with the use of high-performance liquid chromatography.

RESULTS

Average plasma ritodrine levels of patients receiving different intravenous dosages ranged from 27.8 +/- 3.5 to 113.3 +/- 38.8 ng/ml. Levels during oral therapy ranged between 9.8 +/- 3.2 and 13.8 +/- 4.4 ng/ml. In both modes of drug delivery, concentrations were significantly correlated with doses. In patients treated first with intravenous ritodrine and subsequently with the oral form, plasma concentrations during oral therapy averaged 27.7% +/- 18.8% of those obtained during intravenous infusion.

CONCLUSION

Subtherapeutic plasma concentrations might be responsible for the failure to demonstrate clinical benefits of oral ritodrine in prevention of recurrent preterm labor. A twofold to threefold increase in the maximum recommended oral dosage of ritodrine should be considered, especially for patients who had previously required relatively high intravenous infusion rates (> 100 micrograms/min).

The efficacy of oral terbutaline after intravenous tocolysis

OBJECTIVE

Our purpose was to investigate in a prospective, randomized study the efficacy of oral terbutaline after successful intravenous tocolysis in reducing preterm birth.

STUDY DESIGN

Patients between 28 and 35 weeks' gestation with uterine contractions and change in cervical examination were treated with intravenous magnesium sulfate for 12 to 24 hours. After successful tocolysis patients were approached for study participation and randomized to receive either oral terbutaline or no therapy. The dose of terbutaline was individualized to achieve a maternal pulse > 100 beats/min, and terbutaline was continued until 36 completed weeks of gestation. Recurrent preterm labor (contractions with change in cervical examination) for either group was treated with intravenous magnesium sulfate, and subsequent treatment was based on the previous randomization.

RESULTS

Fifty-five patients were enrolled (28 terbutaline, 27 no oral tocolytic). No difference was found between groups with respect to time gained (4.0 +/- 2.7 vs 4.6 +/- 3.1 weeks, p = 0.412), gestational age at delivery (35.6 +/- 2.7 vs 36.1 +/- 2.4 weeks, p = 0.562), > or = 37 weeks at delivery (nine vs 13, p = 0.291), recurrent preterm labor (10 vs four, p = 0.104), recurrent uterine contractions alone (five vs eight, p = 0.527), birth weight (2616 +/- 633 gm vs 2645 +/- 599 gm, p = 0.785), special care nursery admissions (eight vs six, p = 0.759), or neonatal respiratory distress syndrome (three vs two, p = 0.965).

CONCLUSION

The use of oral terbutaline after successful parenteral tocolysis failed to reduce the rate of preterm birth.

Antibiotic treatment of preterm labor with intact membranes: a multicenter, randomized, double-blinded, placebo-controlled trial

OBJECTIVE

Although an association between subclinical intrauterine infection and preterm birth is well established, there is conflicting evidence regarding the benefits of antibiotic administration to women in preterm labor with intact membranes. We attempted to determine the effect of ampicillin-amoxicillin and erythromycin treatment on prolongation of pregnancy, the rate of preterm birth, and neonatal morbidity in patients with preterm labor and intact membranes.

STUDY DESIGN

A multicenter, randomized, double-blinded, placebo-controlled trial was designed and implemented by the Maternal-Fetal Medicine Units Network of the National Institute of Child Health and Human Development. Two hundred seventy-seven women with singleton pregnancies and preterm labor with intact membranes (24 to 34 weeks) were randomly allocated to receive either antibiotics or placebos.

RESULTS

Of the 2373 patients screened for participation in this study in six medical centers, 277 women were enrolled (n = 133 for antibiotics group vs n = 144 for placebo group). In each study group, 60% of patients completed all the study medications. The overall prevalence of microbial invasion of the amniotic cavity was 5.8% (14/239). No significant difference between the antibiotic group and the placebo group was found in maternal outcomes, including duration of randomization-to-delivery interval, frequency of preterm delivery (< 37 weeks), frequency of preterm premature rupture of membranes, clinical chorioamnionitis, endometritis, and number of subsequent admissions for preterm labor. Similarly, no significant difference in neonatal outcomes could be detected between the two groups including respiratory distress syndrome, bronchopulmonary dysplasia, intraventricular hemorrhage, sepsis, and admission and duration of newborn intensive special care unit hospitalization.

CONCLUSION

The results of this study do not support the routine use of antibiotic administration to women in preterm labor with intact membranes.

Preterm birth prevention: where are we?

OBJECTIVE

The purpose of this study was to review the current approaches to preventing preterm delivery.

STUDY DESIGN

The problem of preterm birth was assessed by reviewing the different components that play a role in preterm birth prevention, excluding infection, antibiotic treatment, and tocolytic treatment.

RESULTS

Prevention of preterm labor must initially discriminate those at risk. Positive predictive values of various approaches are currently not adequate enough to warrant intervention. Prevention modalities, in part because of poor prediction, are mostly unproved. Accurate diagnoses of preterm labor remains difficult and confuses analyses of tocolytic agents. Cervicovaginal fetal fibronectin, perhaps in combination with cervical evaluation, shows promise. Early detection programs remain controversial, but most reviews indicate that daily patient contact with high-risk patients gives cause for some optimism. Antenatal maternal glucocorticoid treatment at specific gestational ages improves neonatal outcome.

CONCLUSION

The incidence of preterm birth is rising in the country. However, improved definition of the various components of the problem has provided an improved understanding of the problem. There is a new continuing effort and a search for new and innovative ways to address this vexing national problem.

Dexamethasone reverses the labor-associated myometrial desensitization to beta-adrenergic agonists in the rat

OBJECTIVES

The purpose of our study was to determine the susceptibility of the myometrium to beta-adrenergic agonist-induced desensitization and to determine the ability of dexamethasone to prevent this homologous desensitization.

STUDY DESIGN

Myometrial tissue was collected from nonpregnant, pregnant, and postpartum rats (n > or = 6) 12 hours after injection of either dexamethasone (0.25 mg subcutaneously) or vehicle (corn oil). The ability of isoproterenol to induce and maintain inhibition of contractile activity was determined in vitro. In addition, the density and affinity of beta-adrenergic receptors was estimated by ligand binding and Scatchard analysis.

RESULTS

Dexamethasone significantly increased both the duration of myometrial responsiveness to isoproterenol and the beta-adrenergic receptor number at parturition, but not at other time points. Regardless of pretreatment, the susceptibility of the myometrium to beta-agonist-induced desensitization was greatest around the time of delivery.

CONCLUSIONS

In the rat, beta-adrenergic agonists are least effective in maintaining myometrial inhibition peripartum, although their effectiveness at this time only can be increased by dexamethasone.

Meta-analysis of the literature or of individual patient data: is there a difference?

The use of meta-analyses or overviews to combine formally the results of related randomised clinical trials is becoming increasingly common. However the distinction between analyses based on information extracted from the published literature and those based on collecting and reanalysing updated individual patient data is not clear. We have investigated the difference between meta-analysis of the literature (MAL) and meta-analysis of individual patient data (MAP) by comparing the two approaches using randomised trials of cisplatin-based therapy in ovarian cancer. The MAL was based on 788 patients and the MAP on 1329 and estimated median follow-ups were 3.5 and 6.5 years, respectively. The MAL gave a result of greater statistical significance (p = 0.027 vs p = 0.30) and an estimate of absolute treatment effect three times as large as the MAP (7.5% vs 2.5%). Publication bias, patient exclusion, length of follow-up, and method of analysis all contributed to this observed difference. The results of a meta-analysis of the literature alone may be misleading. Whenever possible, a meta-analysis of updated individual patient data should be done because this provides the least biased and most reliable means of addressing questions that have not been satisfactorily resolved by individual clinical trials.

Interval to delivery in high-risk patients: do tocolytic agents really work?

Some question whether tocolytic drugs reduce uterine activity and prolong gestation. The interval from discontinuance of tocolytics until spontaneous labor and delivery in patients (n = 69) with documented preterm labor (PTL) versus subjects receiving prophylactic tocolytic therapy (n = 41) was studied. Women with documented PTL delivered sooner after cessation of tocolytics (6.1 +/- 6.9 days) than control (C) patients (14.7 +/- 10.8 days, P less than 0.001). Also, 28 of the 69 (41%) patients in the PTL group delivered within 24 h of discontinuation of tocolysis compared to 4 (10%) in the C group (P less than 0.0004). We conclude that tocolytic therapy for documented preterm labor suppresses uterine activity and when these agents are discontinued, contractions return and labor ensues.

Failure of ritodrine to prevent preterm labor in the sheep

OBJECTIVES

The purpose of this study was to determine whether continuous infusion of ritodrine could prevent preterm delivery in sheep.

STUDY DESIGN

Sheep in preterm labor induced by RU 486 (mifepristone) received infusions of either ritodrine (n = 5) or saline solution (n = 5), and the progress of labor was monitored. beta 2-Adrenergic receptor density and function (agonist-induced cyclic adenosine monophosphate production) was measured in myometrial samples from both groups.

RESULTS

Ritodrine initially inhibited labor contractions. This inhibition was only maintained for 16 hours, after which both the amplitude and frequency of electromyographic bursts and contractions returned. The failure of the myometrium to respond to ritodrine (desensitization) was associated with significant reductions in agonist-induced cyclic adenosine monophosphate production and beta 2-adrenergic receptor concentration in myometrial tissue collected from these animals compared with the saline solution-treated controls.

CONCLUSIONS

Continuous infusion of ritodrine to sheep in preterm labor produces only a transient inhibition of contractions. This desensitization is caused by a down-regulation of myometrial beta 2-adrenergic receptors.