Monitoring women at risk for preterm labor

BACKGROUND

Preterm birth is a major cause of perinatal morbidity and mortality. Whether the rate of preterm birth can be reduced by frequent contact between nurses and pregnant women or home monitoring of uterine activity is not known.

METHODS

We randomly assigned 2422 pregnant women with known risk factors for preterm labor (including 844 women who were pregnant with twins) to receive education and to have one of the following: weekly contact with a nurse, daily contact with a nurse, or daily contact with a nurse and home monitoring of uterine activity. The nurses elicited the women's own assessments of their symptoms and signs of preterm labor. The primary end point was the incidence of birth at less than 35 weeks' gestation. Secondary end points included cervical status at the time preterm labor was diagnosed and birth weight.

RESULTS

There were no significant differences among the groups in the incidence of birth at less than 35 weeks (14 percent in the weekly-contact group, 13 percent in the daily-contact group, and 14 percent in the home-monitoring group), in the mean amount of cervical dilatation at the time preterm labor was diagnosed (1.8 cm, 1.5 cm, and 1.4 cm, respectively), or in such neonatal outcomes as birth weights of less than 1500 g or less than 2500 g. However, daily contact with a nurse increased the mean number of unscheduled visits to obstetricians (1.2 in the weekly-contact group, 1.8 in the daily-contact group, and 2.3 in the home-monitoring group) and the proportion of women who received prophylactic tocolytic drugs (12 percent, 14 percent, and 19 percent, respectively).

CONCLUSIONS

Women who have daily contact with a nurse, with or without home monitoring of uterine activity, have no better pregnancy outcomes than women who have weekly contact with a nurse.

Frequency of uterine contractions and the risk of spontaneous preterm delivery

BACKGROUND

The measurement of the frequency of uterine contractions has not been useful for reducing the rate of preterm delivery in randomized trials. Nonetheless, ambulatory monitoring of contractions continues to be used in clinical practice.

METHODS

We assessed the frequency of uterine contractions as a predictor of the risk of spontaneous preterm delivery before 35 weeks of gestation. We enrolled women with singleton pregnancies between 22 and 24 weeks of gestation. The women used a contraction monitor at home to record contraction frequency twice daily on 2 or more days per week from enrollment to delivery or 37 weeks of gestation.

RESULTS

We obtained 34,908 hours of successful monitoring recordings from 306 women. Although more contractions were recorded from women who delivered before 35 weeks than from women who delivered at 35 weeks or later, we could identify no threshold frequency that effectively identified women who delivered preterm infants. The sensitivity and positive predictive value of a maximal hourly frequency of contractions of four or more between 4 p.m. and 3:59 a.m. were 9 percent and 25 percent, respectively, at 22 to 24 weeks and 28 percent and 23 percent at 27 to 28 weeks. Other proposed screening tests, such as digital and ultrasound evaluations of the cervix and assays for fetal fibronectin in cervicovaginal secretions, also had low sensitivity and positive predictive value for preterm labor.

CONCLUSIONS

Although the likelihood of preterm delivery increases with an increased frequency of uterine contractions, measurement of this frequency is not clinically useful for predicting preterm delivery.

Noninvasive uterine electromyography for prediction of preterm delivery

OBJECTIVE

Power spectrum (PS) of uterine electromyography (EMG) can identify true labor. EMG propagation velocity (PV) to diagnose labor has not been reported. The objective was to compare uterine EMG against current methods to predict preterm delivery.

STUDY DESIGN

EMG was recorded in 116 patients (preterm labor, n = 20; preterm nonlabor, n = 68; term labor, n = 22; term nonlabor, n = 6). A Student t test was used to compare EMG values for labor vs nonlabor (P < .05, significant). Predictive values of EMG, Bishop score, contractions on tocogram, and transvaginal cervical length were calculated using receiver-operator characteristics analysis.

RESULTS

PV was higher in preterm and term labor compared with nonlabor (P < .001). Combined PV and PS peak frequency predicted preterm delivery within 7 days with area under the curve (AUC) of 0.96. Bishop score, contractions, and cervical length had an AUC of 0.72, 0.67, and 0.54.

CONCLUSION

Uterine EMG PV and PS peak frequency more accurately identify true preterm labor than clinical methods.

The intrapartum deceleration in center stage: a physiologic approach to the interpretation of fetal heart rate changes in labor

One of the most distinctive features of fetal heart rate recordings in labor is the deceleration. In clinical practice, there has been much confusion about the types of decelerations and their significance. In the present review, we examined uteroplacental perfusion in labor, describe the pathophysiologic condition of decelerations, and explain some of the reasons behind the confusion about the terminology. We summarize recent studies that systematically have dissected the features of variable decelerations that may help to identify developing fetal compromise, such as the slope of the deceleration, overshoot, and variability changes. Although no pattern of repeated deep decelerations is necessarily benign, fetuses with normal placental reserve can compensate fully, even for frequent deep but brief decelerations, for surprisingly prolonged intervals before the development of profound acidosis and hypotension. This tolerance reflects the remarkable ability of the fetus to adapt to repeated hypoxia. We propose that, rather than focus on descriptive labels, clinicians should be trained to understand the physiologic mechanisms of fetal heart rate decelerations and the patterns of fetal heart rate change that indicate progressive loss of fetal compensation.

Use of uterine electromyography to diagnose term and preterm labor

Current methodologies to assess the process of labor, such as tocodynamometry or intrauterine pressure catheters, fetal fibronectin, cervical length measurement and digital cervical examination, have several major drawbacks. They only measure the onset of labor indirectly and do not detect cellular changes characteristic of true labor. Consequently, their predictive values for term or preterm delivery are poor. Uterine contractions are a result of the electrical activity within the myometrium. Measurement of uterine electromyography (EMG) has been shown to detect contractions as accurately as the currently used methods. In addition, changes in cell excitability and coupling required for effective contractions that lead to delivery are reflected in changes of several EMG parameters. Use of uterine EMG can help to identify patients in true labor better than any other method presently employed in the clinic.

Quantitative analysis of contraction patterns in electrical activity signal of pregnant uterus as an alternative to mechanical approach

Monitoring of uterine contraction activity is an important diagnostic tool used during both pregnancy and labour. The strain the pregnant uterus exerts on the maternal abdomen is measured via external tocography. However, limitation of this approach has caused the development of another technique-electrohysterography--which is based on the recording of electrical uterine activity. A computer-aided system is presented, which allows the recording of electrohysterographic signals from the maternal abdomen and their on-line analysis both in time and frequency domains. As a research material, we acquired 108 traces during a 24 h period before labour from a group of patients between 37 and 40 weeks of gestation. The comparison study between electrohysterography and tocography was carried out thanks to the possibility of simultaneous recording of mechanical and electrical uterine activities. The obtained results show that both methods demonstrate high agreement in relation to the number of contractions recognized as being consistent. However, their agreement in relation to the quantitative description of recognized patterns has appeared to be unacceptable to consider these methods as fully alternative. The appropriate way of further development of electrohysterography seems to be spectral analysis. Several spectral parameters describing electrophysiological properties of uterine muscle can be obtained by the use of electrohysterographic signals.

A metaanalysis of home uterine activity monitoring

OBJECTIVE

Our purpose was to assess by metaanalysis the evidence from randomized clinical trials regarding home uterine activity monitoring.

STUDY DESIGN

Six randomized controlled trials of home uterine activity monitoring, the same six trials reviewed by the U.S. Preventive Services Task Force on home uterine activity monitoring, were studied. Data were extracted from published reports of the six trials. In addition, unpublished data were obtained by personal communication from the trials' principal investigators. Insofar as possible, the principle of intention-to-treat was maintained. Data regarding twins were handled by use of numbers of pregnancies rather than numbers of infants as sample sizes. Stratified metaanalyses were conducted according to whether the trial did or did not control in study design for the nursing contact factor that accompanies home uterine activity monitoring. In addition, stratified metaanalyses were conducted for singleton and twin pregnancies. The four outcomes investigated were incidence of preterm birth, incidence of preterm labor combined with cervical dilatation > 2 cm, infant referral to the intensive care unit, and mean birth weight.

RESULTS

Overall, for all pregnancies home uterine activity monitoring was associated with a statistically significant reduction of 52% in risk of preterm labor combined with cervical dilatation > 2 cm (relative risk = 0.48, p = 0.001) and a statistically significant increase of 86 gm in mean birth weight (p = 0.038). When stratified by singleton or twin pregnancy, the pooled results generally differed by strata. Among singleton pregnancies, home uterine activity monitoring was associated with a statistically significant reduction of 24% in risk of preterm birth (relative risk 0.76, p = 0.037) and a statistically significant increase of 126 gm in mean birth weight (p = 0.009). Among twin pregnancies, there was a statistically significant effect of home uterine activity monitoring with a reduction of 56% in risk of preterm labor combined with cervical dilatation > 2 cm (relative risk 0.44, p = 0.005). There were no statistically significant effects found overall and in any stratum with regard to infant referral to the intensive care unit. Metaanalyses of studies that controlled in design for the nursing contact factor that accompanies home uterine activity monitoring showed either no difference or stronger pooled effects compared with metaanalyses of those studies that did not control for nursing contact. This suggests that the potential bias attributed to the nursing contact feature that accompanies home uterine activity monitoring is not as appreciable as home uterine activity monitoring critics have suggested.

CONCLUSIONS

Metaanalysis of existing clinical trial evidence regarding home uterine activity monitoring reveals statistically significant benefits of home uterine activity monitoring. Of the outcomes investigated, home uterine activity monitoring is associated with reductions in risks of preterm birth (in singleton pregnancies only) and preterm labor combined with cervical dilatation > 2 cm, as well as with increased mean birth weight (in singleton pregnancies only).

A multicenter randomized controlled trial of home uterine monitoring: active versus sham device. The Collaborative Home Uterine Monitoring Study (CHUMS) Group

OBJECTIVE

Our purpose was to determine the efficacy of a home uterine activity monitoring system for early detection of preterm labor and reduction of preterm birth.

STUDY DESIGN

A randomized, controlled, double-blinded trial was performed in which pregnant women between 24 and 36 weeks' gestation and at high risk for preterm labor or birth were assigned to receive twice daily nursing contact and home uterine activity monitoring with either active (data revealed) or sham (data concealed) devices. Study end points included mean cervical dilatation and its mean change from a previous visit at preterm labor diagnosis, preterm birth rate, and infant outcomes. Analysis of variance or logistic models including terms for site and group-by-site interaction effects were constructed for all variables.

RESULTS

Of 1355 patients enrolled, 1292 were randomized, 1165 used home uterine activity monitoring devices, and 842 (72.3%) completed the study. Both device groups had similar demographics, enrollment and delivery gestational ages, discontinuation rates, risk factors, birth weights, cervical dilatation at enrollment and at preterm labor diagnosis, change in cervical dilatation at preterm labor diagnosis, rates of preterm labor and birth, and neonatal intensive care requirements. Power to detect a difference in cervical dilatation > or = 1 cm at diagnosis of preterm labor was 0.99 for all risk factors.

CONCLUSIONS

Uterine activity data obtained from home uterine activity monitoring, when added to daily nursing contact, were not linked to earlier diagnosis of preterm labor or lower rates of preterm birth or neonatal morbidity in pregnancies at high risk for preterm labor and birth.

The clinical efficacy of oral tocolytic therapy

OBJECTIVE

Our purpose was to determine whether maintenance oral tocolytic therapy after preterm labor stabilization decreases uterine activity, reduces the rate of recurrent preterm labor and subsequent preterm birth, or improves neonatal outcome.

STUDY DESIGN

Women with documented idiopathic preterm labor stabilized with acute tocolytic therapy were randomized to three groups: placebo, terbutaline 5 mg, or magnesium chloride 128 mg, all given orally every 4 hours. Patients and providers were blinded to group assignment. All subjects were enrolled in a comprehensive system of preterm birth prevention that included preterm labor education, weekly clinic visits, home uterine contraction assessment, daily phone contact, and 24-hour perinatal nurse access.

RESULTS

Of the 248 patients who were randomized, 39 were delivered before discharge and 4 were lost to follow-up, leaving 205 for final analysis: 68 placebo, 72 terbutaline, and 65 magnesium. The terbutaline group had significantly more side effects than the placebo group did. All groups had otherwise similar perinatal outcomes when confounding variables were controlled for. Overall, the three groups had a preterm birth rate < 37 weeks of 55.6% delivery, < 34 weeks of 15.6%, a 20.4% rate of newborn intensive care unit admission, and a mean neonatal length of stay of 6.3 days.

CONCLUSIONS

Maintenance oral tocolytic therapy did not decrease uterine activity, reduce the rate of recurrent preterm labor or preterm birth, or improve perinatal outcome. Overall improvement in perinatal outcome may be achieved with a comprehensive program of preterm birth prevention without the use of maintenance oral tocolytic therapy.

The Icelandic 16-electrode electrohysterogram database

External recordings of the electrohysterogram (EHG) can provide new knowledge on uterine electrical activity associated with contractions. Better understanding of the mechanisms underlying labor can contribute to preventing preterm birth which is the main cause of mortality and morbidity in newborns. Promising results using the EHG for labor prediction and other uses in obstetric care are the drivers of this work. This paper presents a database of 122 4-by-4 electrode EHG recordings performed on 45 pregnant women using a standardized recording protocol and a placement guide system. The recordings were performed in Iceland between 2008 and 2010. Of the 45 participants, 32 were measured repeatedly during the same pregnancy and participated in two to seven recordings. Recordings were performed in the third trimester (112 recordings) and during labor (10 recordings). The database includes simultaneously recorded tocographs, annotations of events and obstetric information on participants. The publication of this database enables independent and novel analysis of multi-electrode EHG by the researchers in the field and hopefully development towards new life-saving technology.

Active phase labor arrest: revisiting the 2-hour minimum

OBJECTIVE

To generate contemporary uterine activity and labor progress data for oxytocin-augmented labor, and assess whether 2 hours of active phase labor arrest with at least 200 Montevideo units justifies cesarean delivery.

METHODS

Five hundred and one consecutive spontaneously laboring term women with abnormally progressive labor were managed by a standardized protocol: oxytocin and intrauterine pressure catheter with an intent to sustain at least 200 Montevideo units for 4 hours or more before cesarean for labor arrest. Uterine activity was measured, and maternal and neonatal outcomes were evaluated. With a sample of this size, the upper 95% confidence interval limit for an event with an observed rate of 1% is below 3%.

RESULTS

During oxytocin augmentation, nulliparas who were delivered vaginally dilated at a median rate of 1.4 cm/hour versus 1.8 cm/hour for parous women. In both groups, the 5th percentile of cervical dilation rate was 0.5 cm/hour. Thirty-eight women experienced labor arrest for over 2 hours despite at least 200 sustained Montevideo units; 23 (61%) achieved a vaginal delivery. Rates of chorioamnionitis and endometritis for the 38 women were 26%. None of their infants sustained a serious complication, including brachial plexus injury, even though three of the 23 vaginal deliveries (13%) were complicated by shoulder dystocia.

CONCLUSION

These data demonstrate that oxytocin-augmented labor proceeds at substantially slower rates than spontaneous labor, and support our previous contention that the criteria of labor arrest for 2 hours, despite at least 200 sustained Montevideo units, are insufficiently rigorous for the performance of cesarean.

Effect of Different Partogram Action Lines on Birth Outcomes

OBJECTIVE

The World Health Organization recommends partograms with a 4-hour action line, denoting the timing of intervention for prolonged labor; others recommend earlier intervention. We assessed the effect of different action line positioning on birth outcomes.

METHODS

A randomized trial of primigravid women with uncomplicated pregnancies, in spontaneous labor at term, was conducted in the northwest of England. Women were assigned to have their labors recorded on a partogram with an action line 2 or 4 hours to the right of the alert line. If progress crossed the action line, diagnosis of prolonged labor was made and managed according to standard protocol. Primary outcomes were rate of cesarean delivery and maternal satisfaction.

RESULTS

A total of 3,000 women were randomly assigned to groups; 2,975 (99.2%) were available for analysis. Questionnaires were completed by 1,929 (65%) women. There were no differences in cesarean delivery rate (136/1,490 compared with 135/1,485; relative risk [RR] 1, 95% confidence interval [CI] 0.80-1.26) or women dissatisfied with labor experience (72/962 compared with 81/967; RR 0.89, 95% CI 0.66-1.21). More women assigned to the 2-hour arm had labors that crossed the action line (854/1,490 compared with 673/1,485; RR 1.27, 95% CI 1.18-1.37); received more intervention (772/1,490 compared with 624/1,485; RR 1.23, 95% CI 1.14-1.33); and, if admitted to the midwife-led unit, were transferred for consultant-led care (366/674 compared with 285/666; RR 1.26, 95% CI 1.13-1.42).

CONCLUSION

In this birth setting, for primigravid women selecting low intervention care, the 2-hour partogram increases the need for intervention without improving maternal or neonatal outcomes, compared with the 4-hour partogram, advocated by the World Health Organization.

CLINICAL TRIAL REGISTRATION

Current Controlled Trials, http://www.controlled-trials.com/isrctn/trial/|/0/78346801.html, ISRCTN78346801.

A maternal complex partial seizure in labor can affect fetal heart rate

We describe a 33-year-old woman who had a complex partial seizure during labor. Intrauterine pressure catheter and fetal heart monitoring during the seizure revealed a strong, prolonged uterine contraction and simultaneous significant fetal heart rate deceleration for 3.5 minutes. This patient demonstrates that complex partial seizures may result in uterine hyperactivity during labor, which may result in fetal hypoxia.

Multicenter randomized clinical trial of home uterine activity monitoring: pregnancy outcomes for all women randomized

OBJECTIVE

Our purpose was to evaluate the impact of home uterine activity monitoring on pregnancy outcomes among women at high risk for preterm labor and delivery.

STUDY DESIGN

Women at high risk for preterm labor at three centers were randomly assigned to receive high-risk prenatal care alone (not monitored) or to receive the same care with twice-daily home uterine activity monitoring without increased nursing support (monitored). There were 339 women with singleton gestations randomized with caregivers blinded to group assignment. The two groups were medically and demographically similar at entry into the study.

RESULTS

Women in the monitored group had prolonged pregnancy survival (p = 0.02) and were less likely to experience a preterm delivery (relative risk 0.59; p = 0.04). Infants born to monitored women with singleton gestations were less likely to be of low birth weight (< 2500 gm; relative risk 0.47, p = 0.003), and were less likely to be admitted to a neonatal intensive care unit (relative risk 0.5, p = 0.01).

CONCLUSION

These data show, among women with singleton gestations at high risk for preterm delivery, that the use of home uterine activity monitoring alone, without additional intensive nursing care, results in improved pregnancy outcomes, including prolonged gestation, decreased risk for preterm delivery, larger-birth-weight infants, and a decreased need for neonatal intensive care.

Cervical examination and tocodynamometry at 28 weeks' gestation: prediction of spontaneous preterm birth

OBJECTIVE

We determined the value of cervical examination and tocodynamometry in identifying nulliparous women at risk for spontaneous preterm delivery.

STUDY DESIGN

At 27.5 +/- 0.8 weeks' gestation 589 women underwent 30 minutes of tocodynamometry, and 570 of these had a cervical examination. Positive findings on these examinations were compared to the rate of spontaneous preterm delivery, defined as those deliveries following the onset of spontaneous labor or premature rupture of membranes.

RESULTS

The two best predictors of spontaneous preterm birth were two or more contractions in 30 minutes and the presence of a soft or medium consistency on cervical examination. As the contractions increased from zero to four or more, the rate of spontaneous preterm delivery rose from 4.2% to 18.2%.

CONCLUSION

In nulliparous women at 28 weeks' gestation, uterine contractions and several components of the cervical examination predicted spontaneous preterm birth.

A simple alternative to parenteral oxytocics for the third stage of labor

OBJECTIVE

To determine the effect of nipple stimulation on uterine activity during the third stage of labor.

METHODS

Randomized controlled study comparing; (i) 15 min of nipple stimulation (n = 6), (ii) routine syntometrine injection (n = 3), (iii) no action/control (N = 5). Uterine activity was continuously measured using the placenta as an in-situ hydrostatic bag connected to a pressure transducer.

RESULTS

Compared to controls uterine pressure was higher during nipple stimulation (103 mmHg vs. 70.8 mmHg, P = 0.04). The duration of the third stage and blood loss tended to be reduced with nipple stimulation compared to controls (20.3 vs. 12.3 min) and (257 vs. 166 ml) respectively but was not significant. Similar differences were observed between syntometrine and control groups.

CONCLUSIONS

For women in developing countries where parenteral oxytocics are not available, nipple stimulation might reduce the incidence of postpartum hemorrhage. A larger trial now seems warranted.

Water birth, more than a trendy alternative: a prospective, observational study

OBJECTIVE

To prospectively assess the effect of water birth on maternal and fetal outcomes in a selected low-risk collective of a tertiary obstetrical unit.

METHOD

In this prospective observational study, 513 patients of a low-risk collective, who requested a water birth, were studied during the years 1998-2002. Primary outcome measurements included the maternal and fetal parameters. Secondary outcome measurements comprised data on the incidence of water births in an interested, low-risk population in an academic hospital.

RESULT

All groups were similar in terms of demographic and obstetric data. Significant differences were observed in maternal outcome parameters, which included the use of analgesia/anesthesia during labor, the duration of first and second stages of labor, perineal tears and episiotomy rate. No differences were seen in all observed fetal outcome parameters including APGAR scores, arterial and venous pH, admission rate to neonatal intensive care unit and infection rate.

CONCLUSION

Water birth is a valuable and promising alternative to traditional delivery methods. The maternal and fetal outcomes were similar to traditional land births. However, currently there still exist some deficits in the scientific evaluation of its safety. Therefore, the selection of a low-risk collective is essential to minimize the risks with the addition of strictly maintained guidelines and continuous intrapartum observation and fetal monitoring. Based on our results and the literature, water births are justifiable when certain criteria are met and risk factors are excluded.

Labor augmentation in an Egyptian teaching hospital

OBJECTIVES

The study documented facility-based obstetric practices for normal labor in Egypt for the first time, to determine their relationship to evidence-based medicine. This paper describes the labor augmentation pattern observed.

METHODS

176 cases of normal labor were observed by medically-trained observers using a checklist. Ward activities were also documented. Observed women were interviewed postpartum and all findings were shared with the providers for their feedback.

RESULTS

Labor was augmented in 91% (165) of the labors observed; this was inappropriate for 93% or 154 women. Reasons for inappropriateness were: oxytocin ordered at the first vaginal exam (41%); in spite of intact membranes (36%), at the time of membrane rupture (42%), in spite of good progress (24%), or a combination of these. The monitoring of oxytocin-receiving women and their babies was inadequate.

CONCLUSIONS

Labor augmentation and monitoring deviated from evidence-based guidelines. Obstacles to implementing protocols need to be explored.

Analysis of uterine contractions: a dynamical approach

The development of suitable techniques for quantifying mechanical and electrophysiological aspects of uterine contractions has been an active area of research. The uterus is a physiological system consisting of a large number of interacting muscle cells. The activity of these cells evolves with time, a trait characteristic of a dynamical system. While such complex physiological systems are non-linear by their very nature, whether this non-linearity is exhibited in the external recording is far from trivial. Traditional techniques such as spectral analysis have been used in the past, but these techniques implicitly assume that the process generating the contractions is linear and hence may be biased. In this tutorial review, a systematic approach using a hierarchy of surrogate algorithms is used to determine the nature of the process generating the contractions produced during labor. The results reveal that uterine contractions are probably generated by non-linear processes. The contraction segments were obtained through simultaneous recordings of the electrical and magnetic signals corresponding to the electrophysiological activity of the uterus and then analyzed. The electrical activity was recorded by placement of non-invasive electrodes onto the maternal abdomen and magnetic activity was recorded non-invasively using a superconducting quantum interference device (SQUID).

A prospective masked observational study of uterine contraction frequency in twins

OBJECTIVE

This study was undertaken to compare uterine contraction frequency in twins versus singletons and to determine if contraction frequency can be an efficient predictor of spontaneous preterm birth in twin gestations.

STUDY DESIGN

Fifty-nine twin and 306 singleton gestations were enrolled between 22 and 24 weeks at 11 centers. Contraction frequency was recorded with a home uterine activity monitor (HUAM) 2 or more times per day on 2 or more days per week until delivery or 36-6/7 weeks. Masked HUAM data were interpreted according to standard protocol. Repeated measures analyses were used to determine whether mean or maximum uterine contraction frequency per hour differed between singleton and twin gestations across gestational age, by time of day, and by delivery before 35 weeks or beyond. Uterine contraction frequency was also evaluated by logistic regression and receiver operator characteristic (ROC) curves as tests to predict spontaneous preterm birth.

RESULTS

There were 34,908 hours of HUAM data recorded by the 306 singleton gestations and 5,427 hours by the 59 women with twins. Uterine contraction frequency was significantly greater in twins (P = .002) compared with singletons, regardless of gestational age. Contraction frequency in twins increased significantly with gestational age and time of day (1600-0359 hours); but was not associated with spontaneous preterm birth. Maximum uterine contraction frequency was associated with preterm birth less than 35 weeks but only in the morning (am) recording (0400-1559) and at the 29- to 30-week gestational age interval. This relationship was modest (odds ratio 1-2) and not consistent across gestational age or between the am and afternoon/evening (pm) monitoring sessions. ROC analysis revealed no contraction frequency that efficiently identified twins who delivered prematurely at any 2-week gestational age interval.

CONCLUSION

Mean uterine contraction frequency was significantly higher for twin gestations than singletons throughout the latter half of pregnancy and between 1600 and 0359 hours but was not higher among twins who delivered less than 35 weeks' gestation. Neither maximum am or pm contraction frequency predicted spontaneous preterm birth less than 35 weeks' gestation in twin pregnancies.