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

Nitric oxide donors for the treatment of preterm labour

BACKGROUND

A number of tocolytics have been advocated for the treatment of threatened preterm labour in order to delay delivery. The rationale is that a delay in delivery may be associated with improved neonatal morbidity or mortality. Nitric oxide donors, such as nitroglycerin, have been used to relax the uterus. This review addresses their efficacy, side effects and influence on neonatal outcome.

OBJECTIVES

To determine whether nitric oxide donors administered in threatened preterm labour are associated with a delay in delivery, adverse side effects or improved neonatal outcome.

SEARCH STRATEGY

A comprehensive search of the Cochrane Pregnancy and Childbirth Group trials register (March 2002) and the Cochrane Controlled Trials Register (The Cochrane Library, Issue 1, 2002) was undertaken.

SELECTION CRITERIA

Randomised controlled trials of nitric oxide donors administered for tocolysis.

DATA COLLECTION AND ANALYSIS

Trial quality assessment and data extraction were done independently by two reviewers.

MAIN RESULTS

Five randomised controlled trials (466 women) were included. Nitroglycerine was the NO donor used in all these trials. Nitric oxide donors did not delay delivery nor improve neonatal outcome when compared with placebo, no treatment or alternative tocolytics such as ritodrine, albuterol and magnesium sulphate. There was, however, a reduction in number of deliveries less than 37 weeks when compared with alternative tocolytics but the numbers of deliveries before 32 and 34 weeks were not influenced. Side effects (other than headache) were reduced in women who received nitric oxide donors rather than other tocolytics. However, women were significantly more likely to experience headache when NO donors had been used.

REVIEWER'S CONCLUSIONS

There is currently insufficient evidence to support the routine administration of nitric oxide donors in the treatment of threatened preterm labour.

The diagnosis and management of preterm labor

Accurate diagnosis of preterm labor remains a problematic issue. New techniques such as transvaginal cervical sonography and fetal fibronectin are increasingly important in diagnosis and intervention planning. Neither test can, at present, be recommended for screening of the general population since there is no effective intervention for a positive test. Future directions in research include development of new tocolytic agents such as COX-2 inhibitors and clarification of the best use of adjunctive therapies such as betamethasone for lung maturity.

Drugs in pregnancy. Drugs for obstetric conditions

For many reasons, including the fear of fetal anomaly, the recognition of pregnancy being a normal physiological process and maternal choice, few drugs are prescribed and used during pregnancy. Nevertheless, there are certain common obstetric conditions that are associated with significant maternal and perinatal morbidity and mortality where drugs play an important and necessary part in treatment. These conditions include termination of pregnancy, threatened preterm labour, induction of labour and post-partum haemorrhage. This chapter deals with the role of drug therapy in these obstetric scenarios. A large amount of obstetric clinical trial research has been dedicated to the management of these conditions.

Clinical and cost-effectiveness of continuous subcutaneous terbutaline versus oral tocolytics for treatment of recurrent preterm labor in twin gestations

OBJECTIVE

To compare the clinical and cost-effectiveness of treating recurrent preterm labor with continuous subcutaneous terbutaline versus oral tocolytics in twin gestations.

STUDY DESIGN

In a retrospective, matched-cohort design, twin pregnancies treated as outpatients with continuous subcutaneous terbutaline were identified from a perinatal database, then matched 1:1 by gestational age at recurrent preterm labor to those receiving oral tocolytics. There were 353 patients per treatment group. A cost model was used to compare antepartum hospital, nursery, and outpatient charges.

RESULTS

Infants of the subcutaneous terbutaline group had greater gestational age at delivery, higher birth weights, and less frequent neonatal intensive care unit admission. Charges for antepartum hospitalization and nursery were significantly less in the subcutaneous terbutaline group, while charges for outpatient services were less for the oral group. Mean total estimated charges were US$17,109 less for those receiving subcutaneous terbutaline.

CONCLUSION

Improved clinical outcomes and decreased nursery utilization suggest cost-effectiveness of outpatient continuous subcutaneous terbutaline versus oral tocolytics for the treatment of recurrent preterm labor.

New developments in the management of preterm labor

Current management of preterm labor has not changed the incidence of preterm delivery; therefore, significant research effort has been concentrated on the search for new methods of management. New tocolytics like inhibitors of cyclooxygenase 2 and nitric oxide donors have been tested in animal models and in preliminary clinical trials with promising results. Inhibition of cervical ripening may be one alternative to tocolysis. This new approach has a potential to be a valuable method of management of preterm labor if human studies confirm the promising results reported in animals. Growing evidence suggests that premature delivery may be associated with infection or fetal growth abnormalities, with dire consequences to the fetus. If these associations are to be included in risk and benefit assessment, then inhibition of preterm labor may prove to be detrimental to the fetus.

Treatment of preterm labor with the oxytocin antagonist atosiban: a double-blind, randomized, controlled comparison with salbutamol

OBJECTIVE

To compare the efficacy and safety of atosiban and salbutamol in the treatment of preterm labor.

STUDY DESIGN

A multicenter, double-blind, double-placebo, randomized, controlled trial. Women (n=241) diagnosed with preterm labor at 23-33 gestational weeks were enrolled and received either atosiban (n=119) or salbutamol (n=122). At randomization, women were stratified by gestational age (< or =28 weeks and >28 weeks). Atosiban (i.v. bolus dose of 6.75 mg, then 300 microg/min for 3h and 100 microg/min for up to 48h) and salbutamol (2.5-45 microg/min) were administered by i.v. infusion for up to 48h. Retreatment with study drug or an alternative tocolytic agent was allowed. Main outcome measures included tocolytic effectiveness which was assessed in terms of the number of women undelivered after 48h and 7 days. Tocolytic efficacy and tolerability were assessed in terms of the proportion of women undelivered and who did not require alternative tocolytic therapy at 48h and 7 days of starting treatment. Safety was assessed in terms of maternal side effects and neonatal morbidity.

RESULTS

Tocolytic effectiveness at 48h was 93.3 versus 95.0% (P=0.67) and after 7 days was 89.9 versus 90.1% (P=0.93) in the atosiban and salbutamol groups, respectively. Tocolytic efficacy and tolerability within 48h was 79.8 versus 75.2% (P=0.15), and after 7 days was 58.8 versus 46.3% (P=0.021) in the atosiban and salbutamol groups, respectively. Maternal adverse events, including serious events, occurred more frequently in the salbutamol group. Neonatal outcomes were comparable between the study groups.

CONCLUSIONS

The oxytocin antagonist atosiban was found to be better tolerated by both mother and fetus than salbutamol, with a comparable neonatal and infant safety profile, and atosiban was as effective as salbutamol in delaying threatened preterm birth. This study supports the clinical use of atosiban in the treatment of preterm labor.

Adverse and beneficial effects of tocolytic therapy

In addition to questions raised about the efficacy of many tocolytics, appropriate concern has been voiced about the safety of these potent drugs. Although some degree of risk for adverse effects with drugs promising a strong therapeutic effect can be accepted, caution needs to be exercised when benefits are marginal or unproven. Unfortunately, some of the tocolytics, most notably the betamimetics and magnesium sulfate, have been found to have considerable potential for adverse maternal cardiovascular and respiratory effects. Although less clearly established, the use of indomethacin appears to be associated with increased fetal and neonatal risks. Concerning magnesium sulfate, in addition to the well-known maternal effects, the accumulating evidence showing an increased frequency of adverse outcomes in the fetus and neonate has led to the recommendations to abandon its use entirely as a tocolytic. Given the limitations of our current state of knowledge, nifedipine would appear to be among the more efficacious and safer tocolytics available to use when properly indicated.

Preterm birth risk assessment

Preterm birth is a leading cause of peripheral morbidity and mortality. The national rate of prematurity approaches 11%. In spite of widespread tocolytic use, the preterm birth rate has actually increased over the past 30 years in the United States. Preterm birth appears to have a multifactorial etiology. Leading theories include infectious, inflammatory or ischemic insult to the uteroplacental barrier, activation of the fetal hypothalamic-pituitary pathway, decreased cervical competence, and pathologic uterine distention. Multiple biochemical and biophysical markers have been studied for their potential to correctly identify women at risk of preterm delivery. Of these, fetal fibronectin and endovaginal ultrasound examination of the cervix have proven effective in predicting which symptomatic women are actually at low risk of preterm birth. Salivary estriol is being studied as a marker for preterm labor and delivery and it too will likely be found to be a reliable risk identifier in a high risk population. However, home uterine activity monitoring has not been shown to decrease the frequency of preterm birth or its neonatal complications.

Pregnancy outcomes and community health: the POUCH study of preterm delivery

In light of the social/ethnic disparity in preterm delivery (PTD) rates, the Pregnancy Outcomes and Community Health (POUCH) Study takes a broad view of the determinants of PTD by attempting to link underlying biological and psychosocial factors. The relationships between placental pathology, maternal biomarkers, and antecedent psychosocial factors are evaluated in three hypothesised pathways of PTD - one characterised primarily by infection, one by maternal vascular disease, and one by premature elevations in corticotropin releasing hormone in the absence of histological evidence of placental pathology. Within each pathway, an emphasis is placed on understanding the roles of stress and of maternal serum alpha-fetoprotein, an early biomarker associated with PTD. The POUCH Study enrolls pregnant women from five Michigan communities. Information about these women and their environments is gathered through detailed interviews and collection of biological samples including hair, urine, saliva, blood, vaginal fluid, and vaginal smear at 15-26 weeks of gestation. We have chosen to focus on the second trimester--a time when pathological processes may have evolved to a detectable stage, but generally before the onset of biological changes that accompany labour. This focus is consistent with the long-range goal of early detection/intervention and prevention of PTD.

Tocolytic therapy for preterm labour: assessing its potential for reducing preterm delivery

Preterm labour (PTL) is a major contributor to preterm delivery (PTD) but delivery is often not preventable by current therapies. We conducted this study to determine the proportion of women with PTL who were and who were not candidates for tocolytic therapy. The cohort comprised residents of Olmsted County, Minnesota who delivered at >20 weeks' gestation in 1985--94 and who experienced PTL. Medical records were abstracted to identify episodes of PTL, its treatment and outcome. We developed an algorithm that accounted for gestation at delivery and pregnancy complications to determine the proportion of pregnancies complicated by PTL that were candidates for tocolytic therapy. Of 651 pregnancies complicated by PTL, a 50% probability sample, stratified by delivery year, were selected and abstracted. The cumulative incidence of PTL ranged from 3.6 to 6.4 per 100 deliveries of live or stillborn infants. Tocolysis was not contraindicated for 49.4% of all women with PTL and for a third of women with only one PTL episode. Delivery was delayed to >35 weeks in 53.8% of candidates for tocolysis. Only an additional 11.7% of women with one or more PTL episodes could have had their PTD delayed beyond 35 weeks if a perfect tocolytic therapy had been available. Many pregnancies complicated by PTL occurred at > or =35 weeks or involved maternal or obstetric factors that contraindicated tocolytic medications. The maximum incremental benefit that could be expected of a new safe and efficacious tocolytic therapy would be to reduce current PTD rates resulting from PTL by about 12%.

Inhibition of cervical ripening by local application of cyclooxygenase 2 inhibitor

OBJECTIVE

Our goal was to test the hypothesis that the previously demonstrated progesterone-independent prolongation of pregnancy in rats treated with cervical application of the cyclooxygenase 2 inhibitor nimesulide is the result of inhibition of cervical ripening.

STUDY DESIGN

Timed-pregnant Sprague-Dawley rats were randomly allocated to treatment with 50 mg nimesulide or vehicle, applied daily on the cervix for 5 days (days 14-18). On day 19 the animals were humanely killed and the cervices were removed. In the first series of experiments the cervices of animals treated with nimesulide (n = 10) or vehicle (n = 10) were examined with a cervimeter, which stretches the cervical tissues in incremental steps of 0.2 mm at 1-minute intervals. A steeper slope through the linear portion of the resulting force-versus-displacement curve indicates more resistance to stretch. In the second series of experiments the cervices of animals treated with nimesulide (n = 11) or vehicle (n = 11) were examined with the Collascope optical device. The cervical content of cross-linked collagen was measured with light-induced fluorescence. The fluorescence spectrum at 390 nm (peak wavelength of the collagen spectrum) was determined. For standardization, the ratio of counts of collagen peak over reference counts was used in the final analyses as an indicator of cross-linked collagen content.

RESULTS

Animals treated with cervical application of nimesulide had significantly higher resistance to stretch than controls (slope: 0.2564 +/- 0.1213 vs 0.1387 +/- 0.0652; P =.019). The cervical content of cross-linked collagen was not significantly different between nimesulide-treated animals and controls (light-induced fluorescence ratios: 3.2134 +/- 0.7390 vs 2.7892 +/- 0.8518; P =.227).

CONCLUSIONS

Treatment with cervical application of the cyclooxygenase 2 inhibitor nimesulide prevents the physiologic process of cervical ripening in late pregnancy. The inhibition is not the result of changes in cross-linked collagen content. Inhibition of cervical ripening with locally administered cyclooxygenase 2 inhibitor may be a potentially valuable treatment for patients at risk for preterm delivery.

Beta-3 versus beta-2 adrenergic agonists and preterm labour: in vitro uterine relaxation effects

OBJECTIVE

1. To investigate the effects of the selective beta-3 adrenoreceptor agonist, BRL 37344, on human pregnant myometrial contractility in vitro. 2. to compare these effects with those of the beta-2 adrenoreceptor agonist, ritodrine.

METHODS

Isometric tension recording was performed under physiological conditions in isolated myometrial strips from biopsies obtained at elective caesarean section. Following pre-incubation with oxytocin (10(-9) M), the effects of cumulative additions of BRL 37344 or ritodrine (10(-8)-10(-3.5) M) on myometrial contractility were investigated. Results were expressed as -log EC50 (pD2) and mean maximal inhibition achieved for both drug compounds.

RESULTS

BRL 37344 exerted a concentration dependant relaxant effect on myometrial contractions in all strips exposed [pD2, 7.26 (0.48) (SEM); mean maximal inhibition 61.98 (4.89%); n = 6]. Similarly, ritodrine exerted a concentration dependant inhibition of myometrial contractility in all strips exposed [pD2 = 7.40 (0.28); mean maximal inhibition 59.49 (3.97%); n = 6]. There was no significant difference between calculated pD2 values (P = 0.65) or mean maximal inhibition achieved (P = 0.79).

CONCLUSIONS

The beta-3 adrenoreceptor agonist BRL 37344 induced relaxation of human myometrial contractions with similar potency to that of the most commonly used tocolytic agent ritodrine. This raises the possibility that the novel beta-3 adrenoreceptor agonists may have potential as therapeutic agents for human preterm labour. In view of their reported reduced cardiovascular side effects their potential clinical use requires further evaluation.

How to diagnose preterm labor: a clinical dilemma

The clinician is faced with many dilemmas in the diagnosis of preterm labor. The tools at hand (no pun intended) yield subjective information and it is difficult to distinguish true labor from false labor. Because preterm labor is multifactorial in cause and can occur in primiparas, estimating risk for the individual patient is difficult. The cause of the preterm labor in the majority of patients is idiopathic; in this group, the use of salivary estriol as a biochemical marker for preterm labor can increase the accuracy of the diagnosis of true labor. It may also lend confidence to the diagnosis of false labor and may allay anxiety and prevent unnecessary interventions. On the horizon are two noninvasive methods: the EMG, to evaluate uterine contractility, and the collascope, to evaluate the cervix. Both show promise and may provide a more objective assessment of risk for preterm delivery among women with symptoms of preterm labor.

Is human myometrial sampling at the time of cesarean delivery safe?

OBJECTIVE

The mechanism for the initiation of human labor remains unknown and is under extensive investigation. Myometrium from patients in labor and not in labor is the ideal tissue to study structural, cellular, and molecular changes that occur during parturition. This study was designed to determine whether myometrial sampling at the time of cesarean delivery increases maternal morbidity.

STUDY DESIGN

This is a prospective cohort study including 118 study and 236 control patients. A full-thickness myometrial sample was obtained from the superior edge of a transverse uterine incision at the time of cesarean delivery. Demographics and standard surgical morbidity data were collected. Statistical methods used included univariate and multivariate analysis.

RESULTS

The study and control groups did not differ significantly with respect to age, gravidity, parity, birth weight, and Apgar scores. The estimated intraoperative blood loss was greater in the control group (P <.02); however, the change in hematocrit level (preoperative vs postoperative values) was not different. There were no significant differences in the rates of endometritis, wound infection, and venous thrombosis up to 6 weeks post partum. When study and control patients were stratified into term in labor, term not in labor, preterm in labor, and preterm not in labor categories and compared for maternal morbidity, there were still no significant differences for any of the outcome measures evaluated.

CONCLUSION

On the basis of our data, human myometrial sampling at cesarean delivery does not increase overall maternal morbidity, irrespective of gestational age and the presence or absence of labor.

Tocolytic effects of a long-acting beta2-adrenoceptor agonist, formoterol, in rats

We have assessed the tocolytic activity of formoterol, a novel long-acting and potent beta2-adrenoceptor agonist, through its production of cyclic adenosine monophosphate, in comparison with ritodrine, a beta2-adrenoceptor agonist used clinically to counter premature delivery. Formoterol and ritodrine inhibited the amplitude and frequency of rat uterine contraction, with IC50 values of 3.8 x 10(-10) and 4.7 x 10(-7) M, respectively. Intravenous administration of formoterol or ritodrine caused inhibition of uterine motility and increased heart rate in a dose-dependent manner. Inhibition of uterine motility by oral administration of formoterol (0.3 and 1 mg kg(-1)) continued for at least 60 min, whereas that with ritodrine (100 mg kg(-1)) persisted for 15 min with rapid recovery thereafter in pregnant rats. The beta-adrenoceptor binding of [125I]iodopindolol to the myometrium of pregnant rats was competitive with formoterol and ritodrine, with Ki values of 0.04 and 6.10 nM, respectively. Formoterol (10(-6)-10(-4) M) and ritodrine (10(-6)-10(-4) M) increased the level of cyclic adenosine monophosphate in lymphocytes in a dose-dependent manner. The results suggested that formoterol caused relaxation of uterine motility through production of cyclic adenosine monophosphate. Thus, formoterol may be useful as a treatment to counter premature delivery.

A prospective, randomized, controlled trial of high and low maintenance doses of magnesium sulfate for acute tocolysis

OBJECTIVE

This study was undertaken to compare a high-dose protocol for magnesium sulfate tocolytic therapy with a low-dose regimen with respect to time needed to achieve tocolysis.

STUDY DESIGN

Patients between 24 and 34 weeks' gestation with preterm labor were included. Patients with ruptured membranes or nonreassuring fetal assessments were excluded. Gravid women received a 4-g loading dose of magnesium sulfate and were prospectively randomly assigned to receive a maintenance dose of 2 or 5 g/h.

RESULTS

The median times to tocolysis were 120 minutes (semi-interquartile range, 30 minutes) in the low-dose group and 90 minutes (semi-interquartile range, 28 minutes) in the high-dose group (P <.001).

CONCLUSION

Patients treated with a higher maintenance dose of magnesium sulfate had a higher frequency of side effects; however, tocolysis was achieved more rapidly and they required shorter admissions to the labor and delivery unit without increased maternal or neonatal morbidity.

Transvaginal ultrasonography examination of the uterine cervix in hospitalised women undergoing preterm labour

OBJECTIVE

Our purpose was to assess the accuracy of cervical mensuration (length, wedging) by transvaginal ultrasonography in the prediction of preterm birth among hospitalised women undergoing preterm labour.

METHOD

Evidence was extracted from articles through a MEDLINE search from 1987 to 1997, followed up by examining the references at the end of pertinent articles. The key words were: pregnancy, cervix, ultrasonography, preterm labour, preterm delivery, cervical length, cervical wedging or funnelling. Final criteria for the selection of the studies were cervical length and/or wedging at internal os in hospitalised women undergoing preterm labour without restriction on the study design.

RESULTS

Nine articles from 12 publications were analysed and incorporated in a discussion. Study design and selection criteria vary among publications. Preterm delivery was the principal outcome, but its definition is not the same according to the authors. The best cut-off for cervical length varies from 18 to 30 mm. The size of the samples is limited. The sensitivity for predicting preterm birth ranges from 68 to 100%, and the specificity ranges from 30 to 78%. Cervical wedging has a sensitivity varying from 23 to 100%, and a specificity ranging from 54 to 90%.

CONCLUSION

Ultrasonography of the cervix is an interesting technology as it is cheap and easy to use. However this technique remains to be assessed before implementing it in daily clinical practice. Finally, studies incorporating transvaginal ultrasonography into interventional trials are needed to determine the efficacy of measuring cervical length in the prevention of preterm birth.

An oxytocin receptor antagonist (atosiban) in the treatment of preterm labor: a randomized, double-blind, placebo-controlled trial with tocolytic rescue

OBJECTIVES

This study was designed to evaluate the efficacy and safety of the oxytocin receptor antagonist atosiban in the treatment of preterm labor.

STUDY DESIGN

A multicenter, double-blind, placebo-controlled trial with tocolytic rescue was designed. Five hundred thirty-one patients were randomized to receive, and 501 received, either intravenous atosiban (n = 246) or placebo (n = 255), followed by subcutaneous maintenance with the assigned agent. Standard tocolytics as rescue tocolysis were permitted after 1 hour of either placebo or atosiban if preterm labor continued. The primary end point was the time from the start of study drug to delivery or therapeutic failure. Secondary end points were the proportion of patients who remained undelivered and did not receive an alternate tocolytic at 24 hours, 48 hours, and 7 days.

RESULTS

No significant difference was found in the time from start of treatment to delivery or therapeutic failure between atosiban and placebo (median, 25.6 days vs 21.0 days, respectively; P =.6). The percentages of patients remaining undelivered and not requiring an alternate tocolytic at 24 hours, 48 hours, and 7 days were significantly higher in the atosiban group than in the control group (all P < or =.008). A significant treatment-by-gestational age interaction existed for the 48-hour and 7-day end points. Atosiban was consistently superior to placebo at a gestational age of > or =28 weeks. Fourteen atosiban-treated patients and 5 placebo-treated patients were randomized at <24 weeks; the incidence of fetal-infant deaths was higher for the atosiban group at <24 weeks. Maternal-fetal adverse events were similar except for injection-site reactions, which occurred more often with atosiban.

CONCLUSIONS

In this trial the treatment of patients in preterm labor with atosiban resulted in prolongation of pregnancy for up to 7 days for those at a gestational age > or =28 weeks, and this occurred with a low rate of maternal-fetal adverse effects. In addition, at a gestational age > or =28 weeks, the infant morbidity and mortality of atosiban-initiated standard care were similar to those with placebo-initiated standard care. Given that all patients in this study were eligible for tocolysis and that, in practice, nearly all patients who are eligible for a tocolytic receive one, the benefit of using atosiban is the placebo-like maternal-fetal side effect profile. These observations support the use of this oxytocin receptor antagonist in the treatment of patients in preterm labor with intact membranes. Efficacy and infant outcome data at <28 weeks are inconclusive.

Regulation of uterine contraction: mechanisms in preterm labor

Preterm labor (PTL) is defined as uterine irritability accompanied by cervical dilation and/or effecement that occurs before 37 weeks gestation. In most cases, PTL becomes preterm delivery (PTD), accounting for 8% to 10% of births in the United States. Fetuses born before 37 weeks' gestation are at risk for a multitude of health and developmental problems. Most perinatal morbidity and mortality in the United States are caused by PTL. It is a costly problem, in both monetary and human terms. Although some risk factors have been identified, they by no means identify, in advance, every case of PTL and PTD. Despite the understandable emphasis on attempts to find and test risk factors that predict PTL, the ultimate benefit--preventing PTD--will come only from an understanding of the physiologic mechanisms of parturition and how to halt those processes when they occur too early. This article reviews current approaches to preventing PTD, describes the biology of myometrial contraction, and discusses recent progress from several laboratories including the authors' that may shed light on approaches to inhibit uterine contractility in the setting of PTL.

Prevention of premature birth: do pediatricians have a role?

The rate of prematurity in the United States has increased over the past 15 years despite a reduction in overall infant mortality and birth weight-specific mortality. The major factors contributing to premature birth exist before pregnancy and therefore will require intervention strategies in the pediatric patient. The high-risk factors include young age at conception (16 years), use of illicit drugs and smoking, poor nutritional status, and certain vaginal infections. Pediatric intervention strategies should include sociologic as well as health education stressing heightened self-esteem and communication skills, avoidance of pregnancy and unprotected sexual activity, avoidance of smoking and drug use, and promotion of a good nutritional status.

Double-blind, randomized, controlled trial of atosiban and ritodrine in the treatment of preterm labor: a multicenter effectiveness and safety study

OBJECTIVE

This study was undertaken to compare the efficacy and safety of intravenous administration of atosiban versus ritodrine for the treatment of preterm labor.

STUDY DESIGN

Women with preterm labor and intact membranes diagnosed at 23 to 33 gestational weeks (n = 247) were randomly assigned to treatment arms and received atosiban (6.75 mg intravenous bolus, 300 microg/min for 3 hours, then 100 microg/min intravenously) or ritodrine (0.10-0.35 mg/min intravenously) for as long as 18 hours. Tocolytic effectiveness was assessed in terms of the numbers of women who had not been delivered after 48 hours and after 7 days. Safety was assessed in terms of maternal side effects and neonatal morbidity. Secondary outcomes included mean gestational age at delivery and mean birth weight. An intent-to-treat analysis was performed with the Cochran-Mantel-Haenszel test.

RESULTS

The proportion of women who had not been delivered at 48 hours was 84.9% (n = 107) in the atosiban group and 86.8% (n = 105) in the ritodrine group. At 7 days 92 women had still not been delivered in both the atosiban (73.0%) and ritodrine (76.0%) groups. Neither of these differences was statistically significant. The incidence of maternal cardiovascular side effects was substantially lower in the atosiban group (4.0% vs 84.3%, P <.001). In addition, intravenous therapy was terminated more frequently as a result of maternal adverse events in the ritodrine group (29.8%) than in the atosiban group (0.8%). The overall occurrences of fetal adverse events in the two treatment groups were comparable. Neonatal morbidity was similar between the treatment groups after adjustment for unbalanced enrollment of women with multiple pregnancies and for gestational ages within treatment groups.

CONCLUSION

Atosiban was comparable in clinical effectiveness to conventional ritodrine therapy but was better tolerated than ritodrine, with no evidence of significant maternal or fetal adverse events. Neonatal morbidity, which was similar between the two treatment arms, was apparently related to the gestational age of the infant rather than to the exposure to either tocolytic agent.

Fetal fibronectin detection as a predictor of preterm birth in actual clinical practice

OBJECTIVE

This study was undertaken to determine whether fetal fibronectin determination is more useful for predicting preterm delivery in clinical practice than it has appeared to be in prospective blinded studies.

STUDY DESIGN

Charts of 151 patients with fetal fibronectin tests performed during 2 years were reviewed. Patients were included if they had symptoms of preterm labor, a singleton pregnancy at 24 to 35 weeks' gestation, intact membranes, and cervical dilatation < or =3 cm.

RESULTS

Complete data were available for 85 tests. For delivery within 7 days after specimen collection the sensitivity, specificity, positive predictive value, and negative predictive value were 89%, 84%, 40%, and 98%, respectively. The positive predictive value was greater (P <.002) than those reported in three prospective studies evaluating delivery within 7 days in patients with symptoms. Gestational age at delivery and birth weight were lower for patients with positive results (P <. 0001 and P <.006, respectively). Patients with positive results were also treated more with tocolysis, corticosteroid use, and hospitalization than were patients with negative results. For direct comparison with studies of patients with cervical dilatation <3 cm, only 4 patients with cervical dilatation of 3 cm were enrolled. All 4 had negative results of fetal fibronectin testing, and their outcomes therefore did not affect the positive predictive value.

CONCLUSION

The positive predictive value of fetal fibronectin measured in actual clinical practice was significantly greater for delivery within 7 days than has been reported in blinded prospective studies.

Maintenance treatment of preterm labor with the oxytocin antagonist atosiban. The Atosiban PTL-098 Study Group

OBJECTIVES

Patients admitted with an acute episode of preterm labor who respond to early intravenously administered tocolysis remain at risk of having subsequent episodes of preterm labor and preterm delivery. Several pharmacologic agents have been used in an attempt to reduce subsequent episodes of preterm labor, and all are associated with significant side effects. Atosiban, an oxytocin receptor antagonist, is effective in the treatment of an acute episode of preterm labor. This study was designed to compare the efficacy and safety of atosiban with those of placebo maintenance therapy in women with preterm labor who achieved uterine quiescence with intravenous atosiban.

STUDY DESIGN

A multicenter, double-blind, placebo-controlled trial was designed for patients in preterm labor who responded to early intravenous treatment with atosiban. Five hundred thirteen patients were randomly assigned to receive maintenance therapy, 252 to receive atosiban, and 251 to receive matching placebo. Maintenance therapy was administered as a continuous subcutaneous infusion, via pump, of 30 microg/min to the end of 36 weeks' gestation. The primary end point was the number of days from the start of maintenance therapy until the first recurrence of labor. A secondary end point was the percentage of patients receiving subsequent intravenous atosiban therapy.

RESULTS

The time (median) from the start of maintenance treatment to the first recurrence of labor was 32.6 days with atosiban and 27.6 days with placebo (P =.02). At least one subsequent intravenous atosiban treatment was needed by 61 atosiban patients (23%) and 77 placebo patients (31%). Except for injection site reactions, adverse event profiles of atosiban and placebo were comparable. There were 4 neonatal deaths reported in the atosiban group and 5 in the placebo group after the start of maintenance therapy. Infant outcomes (including birth weight) were comparable between maintenance and treatment groups.

CONCLUSIONS

Maintenance therapy with the oxytocin receptor antagonist atosiban can prolong uterine quiescence after successful treatment of an acute episode of preterm labor with atosiban. Treatment was well tolerated.

Controversies in tocolytic therapy

In general, tocolytic agents are effective in stopping uterine contractions and in temporarily delaying delivery. The benefit of stopping uterine contractions is dependent on the fetal status and gestational age. The rationale for stopping preterm labor is to improve neonatal outcome. At this time, the best way to improve neonatal outcome would be to assure delivery in a center capable of caring for a preterm infant and prescription of glucocorticoids to decrease the risk of respiratory distress syndrome and other neonatal complications. Intravenous tocolysis for premature labor has found a prominent place in the obstetrician's armamentarium. We recommend the use of magnesium sulfate as first-line therapy. When comparing maternal and fetal risks, side effects, and the safety profile, magnesium sulfate is superior to beta-mimetics; however, there are still significant problems with potential morbidity and mortality for both mother and fetus with any tocolytics. Adjunctive use of indomethacin with magnesium sulfate may be used through 32 weeks for up to 48 hours at a time. Most tocolytics are effective in stopping labor for 48-72 hours. None have been shown to decrease the rate of preterm delivery. Once the uterus is quiescent and intravenous tocolytics are stopped, prolonged use of tocolytics has not been shown to be effective in preventing preterm birth. Tocolytics have significant long-term side effects to the mother's cardiovascular system, carbohydrate metabolism, and the fetal cardiovascular system. Thus, the prolonged use of prophylactic tocolytics after cessation of intravenous medications is not recommended. Tocolytics may be an appropriate therapy during preterm labor vaginal bleeding, ruptured membranes, multiple gestation, or advanced cervical dilatation. In all situations, however, careful guidelines must be observed. These guidelines include: (1) maternal and fetal well-being must be established before tocolytic therapy; (2) causes of preterm labor should be evaluated and treated when possible; (3) the risk/benefit ratio for both the mother and fetus must be re-evaluated on an ongoing basis; (4) when tocolytics are given before pulmonary maturity, then antenatal corticosteroids also should be considered in every case; (5) long-term use of tocolytics is difficult to justify at this time; (6) the safest tocolytic should be used for the shortest amount of time possible. It is doubtful, because of the nature of tocolytics, that newer tocolytics will be developed that will eliminate the problems of preterm delivery. Preterm delivery is an end-stage symptom of a multifactorial disease. Preterm labor is one of the last symptoms in a cascade of biochemical events that lead to preterm delivery. The most appropriate way to end preterm delivery would be to prevent the causes that initiate the cascade that ends in preterm labor. Authors' Note: Literally hundreds of papers have been written in the last 30 years on tocoloysis. For the purposes of space, when studies are summarized in peer-reviewed articles, we have referenced the reviews instead of the individual studies.

Prediction of delivery among women with early preterm labor by means of clinical characteristics alone

OBJECTIVE

This study was undertaken to assess whether individual clinical factors or combinations thereof could be used to accurately predict the risk of delivery within 1 week of admission among women with preterm labor and minimal cervical dilatation.

STUDY DESIGN

We performed a case-control study of patients admitted to our institution with preterm labor and minimal cervical dilatation. A case patient was a patient who sought treatment with uterine contractions between 24 and 34 weeks' gestation with cervical dilatation </=2 cm, who received tocolysis with magnesium sulfate, and who was delivered within 7 days of admission. Control subjects were those who had the same presentation with preterm labor but were not delivered within the first 7 days after admission. The medical records of case patients and control subjects were then abstracted, and information on >70 potential predictors was recorded. Statistical analysis consisted of bivariate and multivariable methods. We also generated a multivariable clinical predictive model with the purpose of detecting a proportion as high as possible of those destined to be delivered within 1 week (high sensitivity). We estimated that we would need 50 case patients and 150 control subjects to detect an odds ratio of 2.5 for risk factors with a prevalence of 20%, an alpha error of.05, a beta error of.20, and a control subject/case patient ratio of 3:1.

RESULTS

Three variables were eligible for inclusion in our logistic models according to the bivariate analyses-bleeding on admission, substance abuse, and admission white blood cell count >/=14,000 cells/microL. The simplest and most favorable model included only 2 variables, bleeding and substance abuse, and yielded a sensitivity of 46% and a specificity of 76%. The full 3-variable model had similar test characteristics. For no model were we able to achieve a sensitivity >/=50%.

CONCLUSION

The results of this case-control study suggest that combinations of clinical factors do not yield an adequate level of discrimination to be used alone for predicting the likelihood of delivery within 1 week among patients with minimal degrees of cervical dilatation.

Efficacy of maintenance therapy after acute tocolysis: a meta-analysis

OBJECTIVE

Our purpose was to analyze published randomized trials assessing the efficacy of maintenance tocolytic therapy after short-term tocolysis in patients with acute preterm labor.

STUDY DESIGN

We supplemented a search of entries in electronic databases with references cited in original studies and review articles to identify randomized trials assessing the efficacy of maintenance tocolytic therapy after resolution of the acute preterm labor episode. Two masked investigators performed independent trial quality evaluation and data abstraction of each trial. We calculated an estimate of the odds ratio and risk difference for dichotomous outcomes, using both a random- and fixed-effects model. Continuous outcomes were pooled with a variance-weighted average of the within-study difference in means.

RESULTS

Of 17 studies identified, 12 met our criteria for meta-analysis. These 12 trials included 1590 patients, including 855 who received maintenance tocolysis and 735 comparison patients who received placebo or no maintenance treatment. Compared with placebo or no treatment, the pooled odds ratio for preventing preterm delivery was 0.95 (95% confidence interval, 0. 77-1.17), and the odds ratio for preventing recurrent preterm labor was 0.81 (95% confidence interval, 0.64-1.03). In addition, use of maintenance tocolytic therapy was not associated with decreased rates of neonatal respiratory distress syndrome, perinatal deaths, or differences in birth weight. Although no difference was noted in mean gestational age at delivery, those receiving tocolytic agents had a longer latency period.

CONCLUSION

Maintenance tocolytic therapy after successful treatment of an acute episode of preterm labor does not reduce the incidence of recurrent preterm labor or preterm delivery and does not improve perinatal outcome. Accordingly, the results of this meta-analysis do not support the use of maintenance tocolytic therapy after successful treatment of preterm labor.

Predicting risk of preterm delivery by second-trimester measurement of maternal plasma corticotropin-releasing hormone and alpha-fetoprotein concentrations

OBJECTIVE

Many women who have preterm labor have abnormally high plasma concentrations of the placental peptide corticotropin-releasing hormone and the fetal product alpha-fetoprotein in early pregnancy. This study was designed to evaluate the ability of these biochemical tests and a clinical risk factor score to prospectively discriminate pregnancies at high risk for preterm delivery.

STUDY DESIGN

Eight hundred sixty women were studied prospectively from the early second trimester until delivery. A risk factor score for preterm delivery was calculated from the clinical history and maternal plasma corticotropin-releasing hormone and alpha-fetoprotein concentrations were measured by radioimmunoassay between 17 and 30 weeks' gestation. The risk factor score, corticotropin-releasing hormone concentration, and alpha-fetoprotein concentration for each woman were expressed as individual odds or likelihood ratios for preterm delivery and as a combined risk estimate derived from the 3 tests.

RESULTS

Sixty women had preterm deliveries (n = 37 spontaneous labor, n = 23 planned deliveries), and these women had significantly higher concentrations of corticotropin-releasing hormone (median 1.92 multiples of the median) and alpha-fetoprotein (median 1.32 multiples of the median) than did women with term deliveries (median 1.00 multiples of the median, P <.001 for both tests), with these abnormalities being evident from early in the second trimester. The risk factor score was >/=10 in 28% of women with preterm delivery and 7% of women with term delivery. The combination of all 3 markers resulted in a higher detection rate and a higher positive predictive value than the risk factor score, corticotropin-releasing hormone concentration, or alpha-fetoprotein concentration alone, correctly discriminating 37% of women who would have preterm deliveries with a false-positive rate of 5%. The positive predictive value was also 37% (odds of being affected given a positive result were 1:1.7).

CONCLUSIONS

The combination of measurement of maternal plasma corticotropin-releasing hormone and alpha-fetoprotein concentrations in the second trimester with risk factor scoring provides a more accurate indicator of the risk of preterm delivery than does risk factor scoring alone. This method of risk assessment may therefore be of use in targeting prevention strategies.

[Analysis of adequacy and effectiveness in the use of tocolytics in preterm labor]

The objective of this study was to assess quality of care for premature labor at public maternity facilities in Rio de Janeiro, Brazil, using referents, indicators, and standards of care derived from scientific evidence. The standard utilized in the process analysis for use of betamimetic tocolytics was 100%, considering the related referents. For outcome analysis, the standard applied was the occurrence of premature delivery in 11% of patients within 24 h and in 24% of patients (referent) within 48 h of hospital admission. Use of tocolytics was observed in 18.7% of patients admitted in premature labor. At gestational age from 28 weeks to 33 weeks and 6 days, especially critical for neonatal survival, tocolytics were used in 32.6% of patients. Premature birth occurred in 59% of patients within 24 h and in 64% within 48 h. These outcomes were consistent with the low rate of utilization of tocolytics. Effectiveness of care for preterm labor measured by rate of premature birth was low. Results of the corresponding process and outcomes analysis were consistent.

Benefits of maternal corticosteroid therapy in infants weighing </=1000 grams at birth after preterm rupture of the amnion

OBJECTIVE

The aim of the study was to determine the effects of antenatal maternal corticosteroid treatment on selected neonatal outcomes in infants weighing </=1000 g at birth after preterm rupture of membranes.

STUDY DESIGN

In a 1-year (1992-1993) prospective observational study, the National Institute of Child Health and Human Development Maternal-Fetal Medicine Units Network collected outcome data for 766 infants who did not have a major fetal anomaly and who had a birth weight </=1000 g (378 were born after preterm rupture of membranes). Only fetuses deemed potentially viable by the obstetrician were included in our analysis. Selected neonatal outcomes were compared between mothers who did and did not receive antenatal corticosteroids. Logistic regression variables included birth weight, sex, race, amnionitis, tocolytic therapies, mode of delivery, and surfactant use.

RESULTS

Two hundred fourteen of the 378 infants whose mothers had preterm rupture of membranes were deemed potentially viable; 62 of these mothers received antenatal steroids and 152 did not. Groups were similar with respect to gestational age, birth weight, race, amnionitis, and delivery mode. Women who received antenatal steroids were more likely to have received tocolysis (P <.001). Univariate and regression analyses controlling for multiple confounders confirmed no neonatal benefits of maternal corticosteroid use.

CONCLUSIONS

Corticosteroid treatment in women with preterm rupture of membranes was of no apparent benefit to neonates weighing </=1000 g.

Clinical issues surrounding the use of terbutaline sulfate for preterm labor

beta-mimetics have been prescribed by physicians to arrest or prevent premature labor for more than 20 years. Although not approved by the Food and Drug Administration (FDA) for tocolytic use, terbutaline sulfate has been the most widely prescribed beta-mimetic in the United States. Recently, the role of terbutaline in the treatment and prevention of preterm labor has been questioned by the FDA. Because the off-label use of drugs is a formally accepted practice in medicine when scientific studies support such use, we reviewed the currently available clinical literature on terbutaline use in various routes of delivery: intravenous, oral, and subcutaneous via infusion pump. This review describes the clinical evidence that supports the safe and effective use of terbutaline as a tocolytic agent in certain patient populations. Practicing physicians should continue to have unrestricted use of terbutaline for tocolysis as one of the few remaining therapeutic options remaining in the fight against preterm birth.

Medication use during the perinatal period

OBJECTIVE

To briefly describe the drug therapy administered during the perinatal period of pregnancy for common maternal and fetal complications, and to identify those agents that should not be used for these conditions.

DATA SOURCES

References were obtained from an ongoing literature search of peer-reviewed obstetric and gynecologic journals and other selected medical and pharmacy journals available in the English language. Primary search vehicle was a weekly review of the tables of contents of nearly 1,300 medical journals provided by Reference Update (Institute of Scientific Information, Philadelphia). MEDLINE searches were also conducted using key terms for each subtopic.

STUDY SELECTION

Specific references were selected for each topic based on the adequacy of their study design, patient population, and a recent publication date. Reviews were used if a large number of primary references would have been required to adequately describe the topic.

DATA EXTRACTION

Most references reflected the current opinions expressed in the Educational (Technical) Bulletin and Committee Opinion series published by the American College of Obstetricians and Gynecologists. Recent, well-conducted studies that arrived at different conclusions were also included.

DATA SYNTHESIS

Data obtained from each reference reflected the conclusions of the authors based on their research or an analysis of the research on others on the appropriate use of the drug(s) for the specific condition being treated.

CONCLUSION

Drug therapy during the perinatal period is frequently required and can be beneficial for the mother, fetus, and newborn. Many complications previously associated with severe morbidity and mortality, such as infections, premature rupture of membranes, preterm labor, hypertension, maternal pain during labor, and postpartum hemorrhage, are now controlled with appropriate pharmacologic therapy. All health professionals who provide services to pregnant women should be knowledgeable in this drug therapy.

Is the attenuation of beta-adrenergic agonist efficacy during labor caused by elevated prostaglandin E levels?

OBJECTIVE

Our purpose was to investigate whether attenuation of beta-adrenergic agonist efficacy during labor is due to elevated prostaglandin E levels.

STUDY DESIGN

beta-Receptor function (response to beta-agonist or forskolin) was tested in mononuclear leukocytes collected from women at term before or during labor. beta-Receptor function was also tested in mononuclear leukocytes of nonlaboring patients after in vitro incubation with oxytocin (1 micromol/L), prostaglandin E2 (10 micromol/L), prostaglandin F2alpha (10 micromol/L), or buffer alone.

RESULTS

Mononuclear leukocytes from women in active labor exhibited a significant attenuation of beta-adrenergic receptor function as a result of reduced adenylyl cyclase activity. This effect could be induced in mononuclear leukocytes from nonlaboring women by preincubation with prostaglandin E but not oxytocin or prostaglandin F.

CONCLUSIONS

Prostaglandin E induces heterologous desensitization of the beta-adrenergic receptor system in mononuclear leukocytes, comparable to that seen during labor. We speculate that during labor the elevated levels of prostaglandin E may induce similar effects on the myometrium, thereby decreasing the efficacy of beta-agonists as tocolytics.

Etiology and prevention of pulmonary complications following beta-mimetic mediated tocolysis

OBJECTIVES

This study documents biological (haematocrit variations) and therapeutic parameters (salbutamol doses, volumes perfused) in two groups tocolysed with salbutamol, one with and the other without APO in order to define the risk factors linked to APO and to establish a standard protocol of management.

STUDY DESIGN

This retrospective study includes data from 68 intravenous salbutamol tocolysis with four resulting APOs, carried out between January 1st, 1993 and December 31st, 1995.

RESULTS

There was an excessive level of salbutamol administered over 48 h in the complicated APO-group (122.5+/-52 mg) opposed to the non-APO group (44.9 21 mg) as well as an overload of perfused solute (3.1+/-1.11) versus (1.9+/-1.11). Blood hemodilution was demonstrated in the APO group with a decrease of haematocrit by over 10% between the admission and the control value. No other risk factor was found.

CONCLUSION

Tocolysis should be administered at the lowest possible perfusion rate with incremental doses as long as the heart rate stays under 120 beats/min and stopped after 48 h. Administration of maximal 11 of solute perfused/day is recommended. For the patient's follow-up we estimate daily input and output fluid to avoid hydric overload, and a daily control of haematocrit whose variation must be less than 10%.

Study of cervicovaginal fetal fibronectin status to guide treatment of threatened preterm labour

A sequential controlled pilot study of 48 women (16 study, 32 controls) was performed to explore the place of bedside fetal fibronectin testing in the management of apparent preterm labour; 80% of the study group were successfully managed without tocolytic therapy, on the basis of fetal fibronectin test results, without detriment to the babies. Rapid bedside fetal fibronectin testing holds promise that protocols for management of women in apparent preterm labour, with intact membranes and without significant cervical dilatation, may be altered so that most of the unnecessary use of tocolytic drugs is avoided.

Hemeoxygenase-1 inhibits human myometrial contractility via carbon monoxide and is upregulated by progesterone during pregnancy

Nitric oxide was proposed as an endogenous inhibitor of myometrial contractility during pregnancy. Carbon monoxide (CO) like nitric oxide increases cGMP and is generated during the degradation of heme to biliverdin IX by hemeoxygenases (HO). Here we report that the expression of both HO-1 (inducible) and HO-2 (constitutive) were > 15-fold higher in pregnant myometrium compared to nonpregnant myometrium (n = 4, P < 0.001, P < 0.005, respectively). Moreover, the activation of the HO-CO pathway by the HO inducer, hemin (10 microM), completely inhibited spontaneous contractility (n = 3). Oxytocin-stimulated contractions (n = 5) were also significantly reduced (P < 0.05) in myometrial strips mounted for isometric recording under 2 g tension in Krebs solution. Reverse transcription-PCR analysis revealed that mRNA encoding HO-1 and HO-2 was undetected in explant cultures of nonlaboring pregnant myometrium under basal conditions, however, exposure to progesterone, but not estradiol-17beta, induced the expression of HO-1 and HO-2 mRNAs. Progesterone also significantly induced HO-1 protein synthesis (n = 4, P < 0.001) while estradiol-17beta had no effect (n = 4). In term (37-42-wk gestation) nonlaboring myometrial explants, CO production was stimulated by progesterone (10(-6) M) (n = 2) and hemin (10 microM) (n = 3) after 2 h of incubation and the effect of hemin was inhibited by 1 h of preincubation with the HO inhibitor tin protoporphyrin IX (20 microM). This study clearly demonstrates the expression of HO in the human myometrium and shows that its induction produces CO that limits uterine contractility in pregnant myometrium indicating a role for the HO-CO-cGMP pathway in the maintenance of the quiescent state of the uterus during pregnancy.