Diltiazem for maintenance tocolysis of preterm labor: comparison to nifedipine in a randomized trial

[Maintenance tocolysis with calcium channel blockers]

AIM OF THE STUDY

The objective of initial tocolysis is to prolong pregnancy for 48 hours, in order to allow fetal lung maturation with corticosteroids. Maintenance tocolysis is defined by the prolongation of tocolytic therapy beyond 48 h. Although the 2002 guidelines of the French College did not recommend to prolong tocolysis beyond 48 h, about 60% of obstetricians prescribe maintenance tocolysis.

METHOD

Nifedipine is the most frequently used treatment for maintenance tocolysis. Five randomised studies and two metaanalyses have compared maintenance tocolysis with nifedipine, with placebo or no treatment.

RESULTS-CONCLUSION

Maintenance tocolysis with calcium channel blockers does not reduce the risk of preterm birth and does not improve perinatal outcome. Tocolytic treatment after 48 hours of initial tocolysis has no beneficial effect (level of evidence 1).

Calcium channel blockers for inhibiting preterm labour and birth

BACKGROUND

Preterm birth is a major contributor to perinatal mortality and morbidity, affecting around 9% of births in high-income countries and an estimated 13% of births in low- and middle-income countries. Tocolytics are drugs used to suppress uterine contractions for women in preterm labour. The most widely used tocolytic are the betamimetics, however, these are associated with a high frequency of unpleasant and sometimes severe maternal side effects. Calcium channel blockers (CCBs) (such as nifedipine) may have similar tocolytic efficacy with less side effects than betamimetics. Oxytocin receptor antagonists (ORAs) (e.g. atosiban) also have a low side-effect profile.

OBJECTIVES

To assess the effects on maternal, fetal and neonatal outcomes of CCBs, administered as a tocolytic agent, to women in preterm labour.

SEARCH METHODS

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (12 November 2013).

SELECTION CRITERIA

All published and unpublished randomised trials in which CCBs were used for tocolysis for women in labour between 20 and 36 completed weeks' gestation.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trial eligibility, undertook quality assessment and data extraction. Results are presented using risk ratio (RR) for categorical data and mean difference (MD) for data measured on a continuous scale with the 95% confidence interval (CI). The number needed to treat to benefit (NNTB) and the number needed to treat to harm (NNTH) were calculated for categorical outcomes that were statistically significantly different.

MAIN RESULTS

This update includes 26 additional trials involving 2511 women, giving a total of 38 included trials (3550 women). Thirty-five trials used nifedipine as the CCB and three trials used nicardipine. Blinding of intervention and outcome assessment was undertaken in only one of the trials (a placebo controlled trial). However, objective outcomes defined according to timing of birth and perinatal mortality were considered to have low risk of detection bias.Two small trials comparing CCBs with placebo or no treatment showed a significant reduction in birth less than 48 hours after trial entry (RR 0.30, 95% CI 0.21 to 0.43) and an increase in maternal adverse effects (RR 49.89, 95% CI 3.13 to 795.02, one trial of 89 women). Due to substantial heterogeneity, outcome data for preterm birth (less than 37 weeks) were not combined; one placebo controlled trial showed no difference (RR 0.96, 95% CI 0.89 to 1.03) while the other (non-placebo controlled trial) reported a reduction (RR 0.44, 95% CI 0.31 to 0.62). No other outcomes were reported.Comparing CCBs (mainly nifedipine) with other tocolytics by type (including betamimetics, glyceryl trinitrate (GTN) patch, non-steriodal anti inflammatories (NSAID), magnesium sulphate and ORAs), no significant reductions were shown in primary outcome measures of birth within 48 hours of treatment or perinatal mortality.Comparing CCBs with betamimetics, there were fewer maternal adverse effects (average RR 0.36, 95% CI 0.24 to 0.53) and fewer maternal adverse effects requiring discontinuation of therapy (average RR 0.22, 95% CI 0.10 to 0.48). Calcium channel blockers resulted in an increase in the interval between trial entry and birth (average MD 4.38 days, 95% CI 0.25 to 8.52) and gestational age (MD 0.71 weeks, 95% CI 0.34 to 1.09), while decreasing preterm and very preterm birth (RR 0.89, 95% CI 0.80 to 0.98 and RR 0.78, 95% CI 0.66 to 0.93); respiratory distress syndrome (RR 0.64, 95% CI 0.48 to 0.86); necrotising enterocolitis (RR 0.21, 95% CI 0.05 to 0.96); intraventricular haemorrhage (RR 0.53, 95% CI 0.34 to 0.84); neonatal jaundice (RR 0.72, 95% CI 0.57 to 0.92); and admissions to neonatal intensive care unit (NICU) (average RR 0.74, 95% CI 0.63 to 0.87). No difference was shown in one trial of outcomes at nine to twelve years of age.Comparing CCBs with ORA, data from one study (which did blind the intervention) showed an increase in gestational age at birth (MD 1.20 completed weeks, 95% CI 0.25 to 2.15) and reductions in preterm birth (RR 0.64, 95% CI 0.47 to 0.89); admissions to the NICU (RR 0.59, 95% CI 0.41 to 0.85); and duration of stay in the NICU (MD -5.40 days,95% CI -10.84 to 0.04). Maternal adverse effects were increased in the CCB group (average RR 2.61, 95% CI 1.43 to 4.74).Comparing CCBs with magnesium sulphate, maternal adverse effects were reduced (average RR 0.52, 95% CI 0.40 to 0.68), as was duration of stay in the NICU (days) (MD -4.55, 95% CI -8.17 to -0.92). No differences were shown in the comparisons with GTN patch or NSAID, although numbers were small.No differences in outcomes were shown in trials comparing nicardipine with other tocolytics, although with limited data no strong conclusions can be drawn. No differences were evident in a small trial that compared higher- versus lower-dose nifedipine, though findings tended to favour a high dose on some measures of neonatal morbidity.

AUTHORS' CONCLUSIONS

Calcium channel blockers (mainly nifedipine) for women in preterm labour have benefits over placebo or no treatment in terms of postponement of birth thus, theoretically, allowing time for administration of antenatal corticosteroids and transfer to higher level care. Calcium channel blockers were shown to have benefits over betamimetics with respect to prolongation of pregnancy, serious neonatal morbidity, and maternal adverse effects. Calcium channel blockers may also have some benefits over ORAs and magnesium sulphate, although ORAs results in fewer maternal adverse effects. However, it must be noted that no difference was shown in perinatal mortality, and data on longer-term outcomes were limited. Further, the lack of blinding of the intervention diminishes the strength of this body of evidence. Further well-designed tocolytic trials are required to determine short- and longer-term infant benefit of CCBs over placebo or no treatment and other tocolytics, particularly ORAs. Another important focus for future trials is identifying optimal dosage regimens of different types of CCBs (high versus low, particularly addressing speed of onset of uterine quiescence) and formulation (capsules versus tablets). All future trials on tocolytics for women in preterm labour should employ blinding of the intervention and outcome assessment, include measurement of longer-term effects into early childhood, and also costs.

The evidence regarding maintenance tocolysis

Preterm delivery is a public health issue of major proportion. More than 12% of deliveries in the United States that occur at less than 37 weeks gestation preterm labor (PTL) represents the largest single reason for preterm birth (PTB). Attempts to prevent PTB have been unsuccessful. This paper of maintenance tocolytic therapy will examine the efficacy and safety of the drugs, both oral and subcutaneous, which have been utilized for prolongation of pregnancy following successful arrest of a documented episode of acute preterm labor. The evidence for oral tocolytics as maintenance therapy as well as parenteral medications for such patients is offered. Finally, the effects in the United States of the Food and Drug Administration (FDA) action on such medications are reported.

Cardiac arrhythmias during pregnancy

OPINION STATEMENT

This article reviews the appropriate evaluation and management of cardiac arrhythmias in the pregnant patient. Any treatment strategy in this patient population has the inherent potential to adversely affect the health of the unborn child. As such, there is no room for empiric therapy in these patients. Adequate arrhythmia documentation is paramount, preferably by noninvasive means. The decision to treat should be based on symptom severity and the risk to both mother and fetus posed by potentially recurring arrhythmia episodes throughout the pregnancy. Minimal symptoms in the setting of a structurally normal heart call for a conservative approach. Less is better. If pharmacologic therapy is justified, drugs with historically demonstrated safety profiles in pregnancy should be tried first. The safety profiles of virtually all drugs used to treat cardiac arrhythmias during human pregnancy are based solely on an accumulation of past clinical experience. Newer antiarrhythmics therefore carry a largely unknown risk. Most inherent rhythm disorders manifest long before a woman reaches childbearing age. Women with previously diagnosed arrhythmias frequently experience a recurrence or worsening of their arrhythmia during the pregnancy. Counseling of these individuals and perhaps preemptive treatment by means such as arrhythmia ablation prior to a planned pregnancy would seem optimal.

The quality of nifedipine studies used to assess tocolytic efficacy: a systematic review

OBJECTIVE

To assess the quality of studies of nifedipine used to treat spontaneous preterm labor.

DESIGN

A systematic review of study quality using a novel validity assessment tool, examining method-specific and topic-specific items in the domains of selection, performance and measurement biases.

DATA SOURCES

Medline (1996-2003), EMBASE (1996-2003), BIOSIS (1993-2003), Current Contents (1995-2003), DERWENT DRUGFILE (1983-2003), Cochrane Database of Systematic Reviews. Bibliographies of existing meta-analyses and systematic reviews of nifedipine as a tocolytic.

METHODS OF STUDY SELECTION

Forty-five studies evaluating the effectiveness of nifedipine were identified.

DATA EXTRACTION

Each study was assessed for 40 method-specific and topic-specific items of quality in duplicate using piloted data extraction forms. Disagreements between assessors were settled by consensus/arbitration.

DATA SYNTHESIS

Very few of the studies complied with adequacy criteria of quality for either method-specific or topic-specific items. There was no improvement in quality over time. The quality of method-specific items was significantly poorer when compared with topic-specific items of quality overall (P<0.0001) and in the domains of selection bias (P<0.0001) and performance bias (P<0.0001).

CONCLUSION

Studies of the effectiveness of nifedipine as a tocolytic are of poorer quality with respect to method-specific items than topic-specific items. These deficiencies should be highlighted in meta-analyses or systematic reviews which measure efficacy and should influence the generation of guideline statements or recommendations for the use of nifedipine as a tocolytic. A large randomized trial fulfilling the quality items is necessary to assess the real efficacy of nifedipine in preterm labor.

Maintenance tocolysis

BACKGROUND

Women who are undelivered after 48 hours of tocolysis remain at increased risk of preterm labour, but it is not clear whether prolonged treatment is effective.

OBJECTIVE

To review the current evidence for the effectiveness of maintenance tocolysis.

METHODS

The results of published systematic reviews were summarised.

RESULTS

Four systematic reviews and two trials published too recently for inclusion were identified. Maintenance tocolysis with beta-agonists and magnesium sulphate was ineffective in prolonging gestation or reducing any adverse fetal outcomes. One trial of maintenance tocolysis with nifedipine was underpowered to rule out an effect on prolonging gestation. One trial using the oxytocin receptor blocker, atosiban, showed that this drug used as maintenance tocolysis does prolong gestation, but the trial was too small to demonstrate any reduction in substantive fetal outcomes.

CONCLUSIONS

There is insufficient evidence to justify the routine use of maintenance tocolysis in preterm labour. It remains plausible that prolongation of gestation might be beneficial in selected cases of very preterm labour where fetal compromise and infection have been ruled out. The only tocolytic that has been shown to prolong gestation when used as maintenance therapy is atosiban.

Oral nifedipine maintenance therapy after acute intravenous tocolysis in preterm labor

AIMS

Our aim was to evaluate the efficacy of maintenance oral nifedipine in pregnant women initially treated with intravenous ritodrine plus verapamil for preterm labor.

METHODS

The study included 73 patients with preterm labor with intact membranes. Patients were randomized to receive either maintenance oral nifedipine therapy (n=37) administered 20 mg every six hours or no treatment (controls, n=36) after discontinuation of acute intravenous tocolysis.

RESULTS

Compared to the control group, the mean +/- SD time gained from initiation of maintenance therapy to delivery (26.65 +/- 18.89 vs. 16.14 +/- 12.91 days, p=0.007) and the gestational age at delivery (37.03 +/- 2.06 vs. 35.1 +/- 3 weeks, p=0.003) were higher in the nifedipine maintenance therapy group. The proportion of patients who required one or more courses of subsequent intravenous therapy and perinatal outcomes were similar in the maintenance therapy and control groups.

CONCLUSIONS

The gestational age and time gained from initiation of maintenance therapy to delivery were longer in women receiving oral maintenance tocolysis with nifedipine. However, maintenance therapy did not decrease the recurrence of preterm labor episodes or improve perinatal outcomes.

Pregnancy and economic outcomes in patients treated for recurrent preterm labor

OBJECTIVE

To compare clinical and cost-effectiveness of treating recurrent preterm labor (RPTL) with oral nifedipine versus continuous subcutaneous terbutaline infusion (SQT).

STUDY DESIGN

Women with singleton gestations prescribed nifedipine for tocolysis following first diagnosis of preterm labor were identified. Women hospitalized with RPTL at <34 weeks were matched by gestational age (GA) after resuming nifedipine (NIF group) with women prescribed SQT (SQT group) after stabilization. Healthcare utilization costs were modeled and compared.

RESULTS

This study analyzed 142 matched pairs. GA at RPTL (matched variable) was 30.4+/-2.6 weeks. GA at delivery was earlier in the NIF group versus the SQT group (35.7+/-3.1 weeks versus 36.6+/-2.1 weeks, p=0.004). Overall, infants from the NIF group had lower birth weights and higher nursery days than infants from the SQT group. Healthcare utilization costs were greater in the NIF group versus the SQT group (37,040+/-47,518 US dollars versus 26,546+/-25,386 US dollars, p=0.014).

CONCLUSION

Treating RPTL with SQT versus oral nifedipine resulted in a later GA at delivery, improved neonatal outcome, and increased cost-effectiveness.

Maintenance therapy with calcium channel blockers for preventing preterm birth after threatened preterm labour

BACKGROUND

Calcium channel blocker maintenance therapy is one of the types of tocolytic therapy used after an episode of threatened preterm labour (and usually an initial dose of tocolytic therapy) in an attempt to prevent the onset of further preterm contractions.

OBJECTIVES

To assess the effects of calcium channel blockers as maintenance therapy on preventing preterm birth after threatened preterm labour.

SEARCH STRATEGY

We searched the Cochrane Pregnancy and Childbirth Group trials register (31 March 2004); MEDLINE (1966 to March 2004) and DARE (June 2003).

SELECTION CRITERIA

Randomised controlled trials of calcium channel blockers used as maintenance therapy to prevent preterm birth after threatened preterm labour, compared with alternative drug therapy, placebo or no treatment.

DATA COLLECTION AND ANALYSIS

Two reviewers independently applied the selection criteria, extracted data from the included study and assessed study quality.

MAIN RESULTS

One trial of 74 women was included. No difference in the incidence of preterm birth was found when calcium channel blocker (nifedipine) maintenance therapy was compared with no treatment. Twenty-five women out of 37 in each group gave birth before 37 weeks (relative risk 1.00, 95% confidence interval 0.73 to 1.37). The trial did not report stillbirths and neonatal deaths prior to discharge. Neurological follow up of the infants was not addressed.

REVIEWERS' CONCLUSIONS

The role of maintenance therapy with calcium channel blockers for preventing preterm birth is not clear. Well designed randomised trials of sufficient size with relevant outcomes are required.

The therapeutic value of maintenance tocolysis: an overview of the evidence

The results obtained from current systematic overview do not support the routine administration of maintenance tocolytic treatment after parenteral tocolytic therapy has halted acute preterm labor. Eliminating or reducing such routine maintenance therapy, therefore, could substantially decrease costs and side effects associated with managing preterm labor without compromising perinatal outcomes. It remains to be elucidated whether it will become possible to accurately identify some groups of pregnancies for which maintenance tocolysis would be beneficial.

Tocolytic treatment for the management of preterm labor: a review of the evidence

OBJECTIVE

Preterm labor is often a prelude to early births and the significant attendant burden of infant morbidity and mortality. Treatment consists of bedrest, hydration, pharmacologic interventions, and combinations of these. We systematically reviewed the effectiveness of tocolytics to stop uterine contractions (first-line therapy) or maintain quiescence (maintenance therapy). Our objective was to evaluate the evidence on the benefits and harms of five classes of tocolytic therapy for treating uterine contractions related to preterm labor--beta-mimetics, calcium channel blockers, magnesium, nonsteroidal anti-inflammatory agents, and ethanol.

STUDY DESIGN

Reports of randomized controlled trials and other study designs in English, French, and German identified from searches of MEDLINE, EMBASE, specialized databases, bibliographies of review articles, unpublished literature, and discussions with investigators in the field were identified. Studies on women with preterm labor between 1966 and February 1999 that met our inclusion criteria were included. Through dual review, we abstracted the following information: study design and masking; definitions of preterm labor and successful tocolysis; patient inclusion/exclusion characteristics; patient demographic characteristics; drug and cointerventions; and numerous birth, maternal, and neonatal outcome measures.

RESULTS

Of the 256 articles evaluated, we abstracted data from 60 first-line and 15 maintenance studies. Of these, 16 first-line and 8 maintenance studies met more stringent requirements for meta-analyses. Studies of first-line tocolysis (grade Fair) reveal a mixed outcome pattern with small improvement in pregnancy prolongation and birth at term relative to placebo. Data were insufficient to show directly a beneficial effect on neonatal morbidity or mortality. Ethanol was less beneficial than, and beta-mimetics were not superior to, other tocolytic options. Maintenance tocolytics (grade Poor) showed no improvements in birth or infant outcomes relative to placebo; these results were confirmed through meta-analysis. In contrast to other tocolytic treatments, maternal harms from beta-mimetics were rated High; all tocolytics were rated as Low risk for short-term neonatal harms.

CONCLUSIONS

Management of uterine contractions with first-line tocolytic therapy can prolong gestation. Among the tocolytics, however, beta-mimetics appear not to be better than other drugs and pose significant potential harms for mothers; ethanol remains an inappropriate therapy. Continued maintenance tocolytic therapy has little or no value.

Calcium channel blockers for inhibiting preterm labour

BACKGROUND

Preterm birth is a major contributor to perinatal mortality and morbidity and affects approximately six to seven per cent of births in developed countries. Tocolytics are drugs used to suppress uterine contractions. The most widely tested tocolytics are betamimetics. Although they have been shown to delay delivery, betamimetics have not been shown to improve perinatal outcome, and they have a high frequency of unpleasant and even fatal maternal side effects. There is growing interest in calcium channel blockers as a potentially effective and well tolerated form of tocolysis.

OBJECTIVES

To assess the effects on maternal, fetal and neonatal outcomes of calcium channel blockers, administered as a tocolytic agent, to women in preterm labour.

SEARCH STRATEGY

We searched the Cochrane Pregnancy and Childbirth Group's specialised register of controlled trials (June 2002), the Cochrane Controlled Trials Register (The Cochrane Library, Issue 2, 2002), MEDLINE (1965 to June 2002), EMBASE (1988 to June 2002), and Current Contents (1997 to June 2002). We also contacted recognised experts and cross referenced relevant material.

SELECTION CRITERIA

All published and unpublished randomised trials in which calcium channel blockers were used for tocolysis for women in labour between 20 and 36 weeks' gestation.

DATA COLLECTION AND ANALYSIS

Standard methods of the Cochrane Collaboration and the Cochrane Pregnancy and Childbirth Group were used. Evaluation of methodological quality and trial data extraction were undertaken independently by three authors. Additional information was sought to enable assessment of methodology and conduct of intention-to-treat analyses. Meta-analysis was conducted assessing the effects of calcium channel blockers compared with any other tocolytic agent. Results are presented using relative risk for categorical data and weighted mean difference for continuous data.

MAIN RESULTS

Twelve randomised controlled trials involving 1029 women were included. When compared with any other tocolytic agent (mainly betamimetics), calcium channel blockers reduced the number of women giving birth within seven days of receiving treatment (relative risk (RR) 0.76; 95% confidence interval (CI) 0.60 to 0.97) and prior to 34 weeks' gestation (RR 0.83; 95% CI 0.69 to 0.99). Calcium channel blockers also reduced the requirement for women to have treatment ceased for adverse drug reaction (RR 0.14; 95% CI 0.05 to 0.36), the frequency of neonatal respiratory distress syndrome (RR 0.63; 95% CI 0.46 to 0.88), necrotising enterocolitis (RR 0.21; 95% CI 0.05 to 0.96), intraventricular haemorrhage (RR 0.59 95% CI 0.36 to 0.98) and neonatal jaundice (RR 0.73; 95% CI 0.57 to 0.93).

REVIEWER'S CONCLUSIONS

When tocolysis is indicated for women in preterm labour, calcium channel blockers are preferable to other tocolytic agents compared, mainly betamimetics. Further research should address the effects of different dosage regimens and formulations of calcium channel blockers on maternal and neonatal outcomes.

Calcium channel blockers as tocolytics

This article reviews the clinical and basic science investigations regarding the safety and efficacy of calcium channel blockers as tocolytic agents. The authors reviewed the English language literature on the pharmacology and clinical applications of calcium antagonists in obstetrics. A MEDLINE (1966-2000) search was performed with the terms "calcium channel blockers," "randomized controlled trial," "preterm labor," "calcium antagonist," "tocolysis," and "nifedipine." References from these data sources were then used to find additional studies. Animal data and clinical trials in humans were included. The safety of these agents was researched in published data from the nonobstetric as well as obstetric literature. The calcium channel blockers most commonly used as tocolytics are nifedipine and nicardipine. These agents act to inhibit calcium influx across cell membranes, thereby decreasing tone in the smooth muscle of the vasculature. They act as profound vasodilatory agents and have minimal effect on the cardiac conduction system. Numerous randomized clinical trials have shown them to be as effective as beta-mimetics and magnesium in achieving tocolysis. When used for tocolysis, calcium antagonists have fewer maternal side effects than other tocolytics and have no adverse effect on fetal outcome.

Calcium channel blockers in the management of preterm labor and hypertension in pregnancy

Calcium channel blockers (CCBs) have the ability to inhibit contractility in smooth muscle cells. CCBs have an already established role in the treatment of non-pregnant hypertension and angina pectoris. Some epidemiological studies found an association between the use of CCBs and an increase in cardiovascular mortality, malignancy, and gastrointestinal bleeding. More recent studies with many more patients and a longer follow-up did not find these associations. In obstetrics CCBs have become increasingly popular for the management of preterm labor and pregnancy-induced hypertensive disorders. Meta-analysis shows that use of nifedipine in comparison with betamimetics is associated with a more frequent successful prolongation of pregnancy in case of preterm labor, resulting in significantly fewer admissions of newborns to the neonatal intensive care unit (NICU), and is associated with a lower incidence of respiratory distress syndrome. No adverse fetal side effects in humans have been reported with the use of nifedipine for obstetric indications. Nifedipine is an effective and safe drug to use when tocolytic therapy is indicated for preterm labor. In preeclampsia nifedipine effectively lowers blood pressure and can be a good alternative for (di) hydralazine.

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.