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

Neonatal periventricular-intraventricular hemorrhage after maternal beta-sympathomimetic tocolysis. The March of Dimes Multicenter Study Group

OBJECTIVE

Our objective was to determine if the rate of periventricular-intraventricular hemorrhage is increased in the offspring of women who received a beta-sympathomimetic agent as part of the management of preterm labor.

STUDY DESIGN

This retrospective study consists of 2827 women who were delivered of a singleton, live infant free of congenital neurologic anomalies between 25 and 36 completed weeks of gestation during a multicenter preterm birth prevention trial. The data were analyzed, adjusting for type of tocolytic agent, race, infant sex, gestational age, birth weight, health care center, route of delivery, indication for delivery, intrapartum fetal distress, respiratory distress syndrome, and neonatal sepsis.

RESULTS

The overall incidence of periventricular-intraventricular hemorrhage in this population was 5.6%. In a univariate analysis in which no adjustment was made for potentially confounding variables, beta-sympathomimetic tocolysis was found to be associated with nearly a fourfold increase in the incidence of periventricular-intraventricular hemorrhage when compared with the use of either magnesium sulfate or no tocolytic agent. The results of a multivariate regression analysis revealed that beta-sympathomimetic agents were associated with a statistically significant increase in the overall incidence of periventricular-intraventricular hemorrhage (odds ratio 2.47, 95% confidence interval 1.34 to 4.56, p = 0.004) and a similar, but not significant, increase in the incidence of grades 3 and 4 periventricular-intraventricular hemorrhage (odds ratio 2.50, 95% confidence interval 0.96 to 6.48, p = 0.06).

CONCLUSION

beta-Sympathomimetic tocolytic therapy may be associated with a more than twofold increase in the incidence of neonatal periventricular-intraventricular hemorrhage.

Treatment of preterm labor with the beta-adrenergic agonist ritodrine

BACKGROUND

Beta-adrenergic agonists are commonly used to arrest premature labor. Although treatment of preterm labor with these agents can delay delivery by 24 to 48 hours, the potential risks and benefits to the mother and infant before and after delivery have not been adequately assessed.

METHODS

We randomly assigned 708 women with preterm labor at six hospitals to receive an intravenous infusion of either the beta-adrenergic agonist ritodrine (n = 352) or placebo (n = 356). Assignment was made with stratification according to four categories of gestational age (20 to 23 weeks, 24 to 27 weeks, 28 to 31 weeks, and 32 to 35 weeks). The primary objective was to assess the effect of ritodrine on perinatal mortality. Secondary objectives were the evaluation of the causes of perinatal death, the extent to which delivery was delayed with ritodrine, and the effects on birth weight, maternal morbidity, neonatal morbidity, and infant morbidity at 18 months of postnatal age, corrected for preterm delivery.

RESULTS

Among the 771 infants born to the women in the study (including 63 pairs of twins), there were 23 deaths (6.1 percent) in the ritodrine group and 25 deaths (6.4 percent) in the placebo group (event-rate difference, -0.3 percent; 95 percent confidence interval, -3.7 percent to 3.1 percent). There was no difference between the groups in the extent of delay of delivery, the incidence of delivery before 37 weeks' gestation, the proportion of babies weighing less than 2500 g, or measures of neonatal morbidity. Maternal morbidity (such as chest pain and cardiac arrhythmias) occurred more frequently but not exclusively in the ritodrine group. One infant born to a woman in the ritodrine group and five infants born to women in the placebo group had cerebral palsy (P = 0.09). There was a slight but not significant trend toward an improved score on the Bayley Psychomotor Development Index at 18 months of age among the infants of the ritodrine-treated women.

CONCLUSIONS

We found that the use of ritodrine in the treatment of preterm labor had no significant beneficial effect on perinatal mortality, the frequency of prolongation of pregnancy to term, or birth weight.

Multicenter randomized clinical trial of home uterine activity monitoring for detection of preterm labor

Home uterine activity monitoring has been described as an effective means of detecting uterine contractions, but controversy exists whether it is home uterine activity monitoring or increased nursing support in conjunction with it that contributes to earlier detection of preterm labor. In this study 377 women at risk for preterm labor from three centers were prospectively, randomly assigned to high-risk prenatal care alone (not monitored) or to the same care with twice-daily home uterine activity monitoring without increased nursing support (monitored). The two groups were medically and demographically similar at entry into the study. Routine visits, nonroutine visits, and gestational age at diagnosis of preterm labor were similar in both groups. Preterm labor occurred in 41 of 198 monitored and 39 of 179 not monitored patients. Mean cervical dilatation was 1.4 cm in 41 monitored compared with 2.5 cm for 37 not monitored (p = 0.0006); 73.1% of monitored and 27.5% of not monitored had preterm labor detected before 2 cm dilatation (p = 0.00009). Neonatal outcome of singleton pregnancies showed greater birth weight, fewer days in the neonatal intensive care unit, and fewer babies requiring oxygen therapy and mechanical ventilation in the monitored group. The better outcomes are probably due to the increased likelihood of diagnosis of preterm labor before advanced cervical dilatation with home uterine activity monitoring, thus providing the clinician with a better chance to initiate tocolytic therapy directed at improving pregnancy outcome.

Oral tocolysis with magnesium chloride: a randomized controlled prospective clinical trial

A prospective randomized clinical trial was conducted to assess the efficacy and safety of enteric-coated magnesium chloride (SLOW MAG) as an oral tocolytic agent. Seventy-five patients between 24 and 34 weeks' gestation who were treated with intravenous magnesium sulfate for a first episode of preterm labor were enrolled. After a 12-hour contraction-free period on intravenous therapy, patients were randomized by sealed envelope to one of three groups: group 1, SLOW MAG (535 mg every 4 hours); group 2, oral ritodrine (20 mg every 4 hours); or group 3, no therapy (control). Patients receiving oral therapy were treated until delivery or completion of 36 weeks' gestation. No difference was found between groups with respect to time gained with the use of oral therapy or number completing 36 weeks' gestation. Therapy with enteric-coated magnesium chloride was associated with significantly fewer side effects (20%) as compared with ritodrine (48%) (p less than 0.01). Our results suggest that compared with ritodrine, enteric-coated magnesium chloride is as effective in prolonging pregnancy and preventing recurrent preterm labor. However, neither enteric-coated magnesium chloride nor ritodrine appeared to be any more effective in the prevention of preterm delivery than observation alone.

Preterm birth prevention: an evaluation of programs in the United States

During the last decade several programs were established to prevent the onset of preterm labor and facilitate its early identification and treatment. Although these prevention programs shared a similar goal, they varied in their primary outcome focus, target populations, study designs, and specific intervention components. Their initial reports were promising; however, subsequent evaluations of efforts in the United States produced mixed results. The current literature is suggestive of the benefits of programs to prevent preterm labor and delivery, but methodologic differences among them and deficiencies in the reported evaluations have rendered a final verdict equivocal. Many studies using historical or geographic controls found positive results, whereas randomized, controlled trials did not find a significant impact. Positive results were found in studies using low-risk populations, but investigations of high-risk patients noted little effect. Together with continued research on the factors that underlie the onset of labor, additional assessment of these programs and their individual intervention components appears to be necessary.

The use of micronized progesterone in the treatment of menace of preterm delivery

The results of a study concerning the treatment of acute menace of preterm labor are given: beta-mimetics were administered intravenously in all cases (44) and micronized progesterone or placebo was administered orally after classical double-blind randomization (22 cases in each group). The mean index of pregnancy prolongation was the same in both groups. However the mean duration of the intravenous perfusion and the mean quantity of beta-mimetics administered intravenously were significantly reduced in the progesterone group (P less than 0.01). The mean duration of hospital stay was also significantly reduced (P less than 0.05). Cost and risks are finally significantly lessened.

The effects of indomethacin and a beta-sympathomimetic agent on the fetal ductus arteriosus during treatment of premature labor: a randomized double-blind study

To study the effect of maternal indomethacin or nylidrine hydrochloride treatment on the fetus ductus arteriosus and the pulmonary artery, 27 women with threatened preterm labor between 24 and 34 weeks' gestation were studied by echocardiography. Fourteen women were treated with indomethacin and 13 with nylidrin. Both systolic and diastolic velocities in the ductus increased after administration of indomethacin indicating constriction in nine fetuses, and exceeded the corresponding velocities in the fetuses of the nylidrin group (p = 0.001). However, there were no changes in pulmonary artery flow velocities (p greater than 0.5). In the indomethacin group, there was a significant linear positive relationship between the gestational age and the change in ductal flow velocity. Three of the nine patients with ductal constriction also had tricuspid regurgitation. These findings indicate that indomethacin, not nylidrin, causes transient constriction of the ductus arteriosus and the constrictive response increases with the gestational age. We recommend echocardiographic surveillance of fetal hemodynamics when prostaglandin synthesis inhibitors are used in the treatment of spontaneous preterm labor.

Awaiting cervical change for the diagnosis of preterm labor does not compromise the efficacy of ritodrine tocolysis

We retrospectively studied 209 patients treated with ritodrine hydrochloride to determine whether change in cervical effacement or dilatation during a period of observation before therapy would result in decreased efficacy of ritodrine, as measured by delivery delays of 48 hours, 1 week, or until greater than or equal to 37 weeks' gestation; neonatal intensive care unit admission; and neonatal respiratory distress syndrome. Patients who were greater than or equal to 3 cm dilated on admission were at high risk of therapy failure by all outcome measures compared with patients less than 3 cm dilated. For patients less than 3 cm dilated on admission, there was no difference in outcome when patients treated for contractions only were compared with those treated after change in effacement or dilatation had been documented. We conclude that awaiting change in cervical effacement or dilatation to be more certain of the diagnosis of preterm labor will not compromise the efficacy of ritodrine tocolysis.

The endocrinology of parturition in the human

Current evidence suggests that oestrogens, progesterone, relaxin, the prostaglandins, and oxytocin are all hormones concerned to a major degree with the onset and maintenance of parturition. Oestrogens, relaxin, and the prostaglandins are particularly involved with cervical ripening, while prostaglandins, progesterone and oxytocin are more involved in regulating myometrial contractility. Catecholamines may also have some regulatory function in relation to uterine contractions. Progesterone dominance during pregnancy is associated with a firm closed cervix, few myometrial gap junctions, low calcium levels in the cells, and a quiescent myometrium. At term, a change in the oestrogen/progesterone balance favours cervical ripening and increased uterine activity. Of particular importance at the level of the muscle cell are changes in the number of oxytocin receptors; a complex interaction between cAMP and phosphoinositide metabolism governs the intracellular level of calcium, thus regulating contractile activity.

Prediction of preterm delivery: is it substantially improved by routine vaginal examinations?

The ability of routine vaginal examinations to improve the prediction of preterm delivery was assessed in a group of 6909 women who were registered at each prenatal visit and on whom this examination had been carried out. We compared two risk scores, one including known risk factors (maternal characteristics and symptoms reported by women), and the other including these factors and the findings of vaginal examination. These risk scores were computed by multiplying the adjusted odds ratio estimations obtained by logistic regressions. The prediction of preterm delivery was improved significantly by vaginal examination at 25 to 28 weeks' and 29 to 31 weeks' gestation. However, the improvement was not very large: when 30% of nulliparous women were classified as high risk at 29 to 31 weeks, the sensitivity was 55% when considering only the risk factors and 63% when adding the findings of vaginal examination; the percentages were 52% and 55%, respectively, for parous women. These results partially explain why the medical practice of routine vaginal examinations varies from country to country.

How accurate is a woman's diagnosis of threatened preterm delivery?

During a 1-year period all women entering hospital with signs or symptoms that could herald preterm delivery were studied. The primary complaints of these 178 women were contractions in 70, watery discharge in 59, bloody discharge in 33, and abdominal pain in 16. These complaints were considered as confirmed threats of preterm delivery if the woman was delivered or received tocolysis within 48 h (n = 63; 35%); they were labelled as an unconfirmed threat if the woman was allowed to return home without further action within 48 h (n = 45; 25%). Overall, 75% of the women were correct in their estimation that something was wrong in that they either gave birth or were admitted for greater than 48 h for diagnostic or therapeutic measures. Parity had only a small influence on women's predictive ability. It is concluded that efforts to increase women's awareness of the significance of various symptoms are not likely to contribute much to improvement in the early diagnosis of preterm labour. Greater effect can be anticipated from the development of methods to differentiate between contractions that will or will not lead to early delivery.

Warning symptoms, uterine contractions, and cervical examination findings in women at risk of preterm delivery

The presence of various reputed warning signs of preterm labor, the frequency of contractions, and the presence of cervical examination findings and their value in predicting preterm labor and spontaneous preterm delivery were assessed. The frequency of contractions and all cervical examination findings increased during pregnancy, as did backache, pressure, and cramping. The frequency of diarrhea, discharge, and bleeding remained constant. Of the various warning signs, only diarrhea and discharge were associated with the diagnosis of preterm labor. None of the warning signs were associated with spontaneous preterm delivery. Various patterns of contractions tended to be associated with higher rates of preterm labor and preterm delivery, but results were generally not statistically significant. Most cervical examination findings were statistically associated with both preterm labor and preterm delivery.

Efficacy, safety and tolerance of oral sustained-release ritodrine given after intravenous administration in the treatment of premature labor

45 patients in premature labor entered the study, four dropped out for administrative reasons. The remaining 41 patients started all with an intravenous treatment followed by oral treatment with sustained-release ritodrine at a daily dosage of 120 mg per day until the 36th week of gestation. The mean gestational age at entry was 31.26 weeks +/- 3.27 and at delivery 37.76 weeks +/- 2.11 or a mean gain in days of 44.61 days +/- 20.85. A cluster analysis splitting the patients into four groups regarding the gestational age at entry and the Baumgarten tocolytic index showed that even the high-risk patients benefit remarkably by the treatment. The side effect rate was low as well for palpitation as for tremor. The patient compliance was excellent. No neonatal deaths or stillborns occurred during this study.

Perinatal factors associated with the respiratory distress syndrome

Perinatal factors related to the incidence of respiratory distress syndrome were analyzed by the multiple logistic regression statistical method in 263 mothers and their 298 offspring delivered between 24 and 35 weeks' gestation in a 1-year period in a regional referral perinatal center. The risk of respiratory distress syndrome in white infants rose with decreasing gestational age (p less than 0.0001) while prolonged rupture of membranes of greater than 24 hours in the absence of maternal infection (28% of cases) was highly protective (p less than 0.0001). Compared with vaginal delivery, cesarean delivery without labor increased the risk of respiratory distress syndrome (p = 0.03). The administration of tocolytic drugs was unrelated to the incidence of respiratory distress syndrome, but corticosteroid therapy given at least 72 hours before delivery was protective (p = 0.03). Male and female infants were equally at risk for respiratory distress syndrome as were black and white infants, but other races had a lower incidence (p = 0.004). Infants with respiratory distress syndrome were on mechanical ventilators longer than those with other respiratory illnesses.

A retrospective study of all low birth-weight preterm babies born in BMH Rinteln between 1980-1989

A retrospective study was undertaken of all preterm babies born in BMH Rinteln between 1980-88 weighing less than 2500g. The total proportion of low birth weight babies was 7% and 58% of these were preterm (454 babies). Sixty per cent of women presented after the spontaneous rupture of membranes or in established labour. Conservative management of ruptured membranes, whilst not leading to life-threatening sepsis, did not significantly prolong pregnancy. Sixteen percent of the babies were very low birth weight (under 1500g). Delivery of these infants by Caesarean section when presenting by the breech improved survival, although this was not statistically significant. Thirty percent of all babies were delivered by Caesarean section before 36 weeks, reflecting obstetric emergencies in the mother which predisposed to preterm delivery. Neonatal survival depended on both gestational maturity and birth weight and was not significantly better in babies who were low birth weight for gestational age. These infants however represented 75% of the still-births and congenital abnormalities. Sixty percent of the mothers smoked and 50% had other identifiable risk factors for preterm delivery; 20% of the multiparous patients had previously experienced a perinatal death, preterm delivery or had a baby with intra-uterine growth retardation. It is suggested that preterm delivery is a significant problem in an Army population despite full employment, adequate housing and comprehensive medical care. Attempts to stop labour are unlikely to be successful. Effort should be made antenatally to identify those women who may be at risk of "idiopathic" preterm labour, as patient education programmes have been shown to decrease the incidence.

The early diagnosis of impending premature labour

Early diagnosis of impending premature labour offers the possibility of early and effective tocolysis. This paper reviews recent work which has suggested that excessive uterine contractility or early cervical dilatation during pregnancy would provide this early diagnosis. Since marked uterine contractility and cervical dilatation can occur in pregnancy which proceeds to term, however, these features may not be specific enough predictors of preterm labour for clinical use. The evidence is also reviewed that the presence or absence of fetal breathing movements (FBM) predicts the outcome of preterm labour. This finding has now been confirmed in four centres outside Oxford. For women admitted in preterm labour, an expertly performed real-time ultrasound scan has now become an essential investigation. Since more than 50% of preterm 'labours' appear to subside spontaneously without tocolysis, a knowledge of the presence or absence of FBM should avoid unnecessary treatment and ensure that clinical efforts are concentrated on patients most in need.

A national survey on preterm labor

A national survey was conducted to examine the American obstetricians' approach to management of preterm labor. Multiple-choice questionnaires were mailed to all current members of the Society of Perinatal Obstetricians and 750 randomly selected diplomates of the American College of Obstetricians and Gynecologists. Respondents included 249 members of the Society of Perinatal Obstetricians and 441 fellows of the American College of Obstetricians and Gynecologists. Analysis of the replies reflects wide variations among American obstetricians' criteria to diagnose preterm labor, choice of tocolytic agent, use of amniocentesis, and use of corticosteroids. Significant differences were found between the two groups in many aspects of diagnosis and management of preterm labor. However, the replies reflect a high degree of awareness of and many instances of first hand experience with severe beta-adrenergic therapy complications, including maternal death. These findings emphasize the need for caution in selection of patients for beta-adrenergic tocolytic therapy and judicious use of these agents.