SMFM Papers www.AJOG.org

Labor patterns in twin gestationsHeidi K. Leftwich, DO; Mary N. Zaki, MD; Isabelle Wilkins, MD; Judith U. Hibbard, MD

OBJECTIVE: To compare labor progression in twin vs singleton RESULTS: A total of 891 twin gestations were compared with 100,513

gestations.

STUDY DESIGN: Retrospective review of electronic database createdby Consortium on Safe Labor, reflecting labor and delivery informationfrom 12 clinical centers 2002-2008. Women with twin gestations,cephalic presentation of presenting twin, gestational age�34 weeks,with �2 cervical examinations were included. Exclusion criteria werefetal anomalies or demise. Singleton controls were selected by thesame criteria. Categorical variables were analyzed by c2; continuousby Student t test. Interval censored regression was used to determinedistribution for time of cervical dilation in centimeters, or “traversetimes,” and controlled for confounding factors. Repeated-measuresanalysis constructed mean labor curves by parity and number offetuses.

From the Division of Maternal-Fetal Medicine (Drs Leftwich, Wilkins, and HibbObstetrics and Gynecology (Dr Zaki), University of Illinois at Chicago, Chicag

Received March 15, 2013; revised May 6, 2013; accepted June 10, 2013.

Supported by the Intramural Research Program, Eunice Kennedy Shriver NaChild Health and Human Development, National Institutes of Health, throughHHSN267200603425C; University of Illinois at Chicago (UIC) Center for ClinScience (CCTS), award no. UL1RR029879 from the National Center for Res

Institutional Review Board #2007-0656, exp 6/15/13.

The authors report no conflict of interest.

Presented at the 33rd annual meeting of the Society for Maternal-Fetal MediciFeb 11-16, 2013.

0002-9378/free � ª 2013 Mosby, Inc. All rights reserved. � http://dx.doi.org/10.1016

For Editors’ Commentary, see Contents

254.e1 American Journal of Obstetrics & Gynecology SEPTEMBER 2013

singleton controls. Twin gestations were more often older, white orAfrican American, earlier gestational age, increased prepregnancybody mass index, and with lower birthweight. There was no differencein number of prior cesarean deliveries, induction, or augmentation, orepidural use. Median traverse times increased at every centimeterinterval in nulliparous twins, in both unadjusted and adjusted analysis(P< .01). A similar pattern was noted for multiparas in both analyses.Labor curves demonstrated a delayed inflection point in the laborpattern for nulliparous and multiparous twin gestations.

CONCLUSION: Both nulliparous and multiparous women have slowerprogression of active phase labor with twins even when controlling forconfounding factors.

Key words: labor curves, pregnancy, twins

Cite this article as: Leftwich HK, Zaki MN, Wilkins I, et al. Labor patterns in twin gestations. Am J Obstet Gynecol 2013;254.e1-5.

he rate of multiple gestations has

T dramatically risen over the past 2decades, due both to increasing maternalage and to the widespread use of assistedreproductive technologies (ART).1,2

With this increase in twin gestationscomes an increased risk of morbidity toboth mother and neonate; one impor-tant source of morbidity is cesarean de-livery. According to Lee et al, a dramaticincrease in cesarean delivery rates amongtwin gestations has been observed, risingfrom 53.4% to 75.0% between 1995 and2008.3 Although some of the rise in ce-sarean rates could be from providerchoice to forego labor altogether, those

women undergoing induction of laborwere also noted to have an increase incesarean delivery from 26.3% to 32.5%.3

Because the inaugural paper in the1950s, obstetricians have referred to theFriedman curves to define labor pro-gression; but labor progress in twingestations was not addressed in Fried-man’s original work.4,5 Recent publishedliterature suggests a need for revised la-bor curves in the general obstetric pop-ulation.6-8 This may be true for2 different reasons. Our contemporarypopulation and obstetric practice, such

ard), Department ofo, IL.

tional Institute ofcontract no.ical and Translationalearch Resources.

ne, San Francisco, CA,

/j.ajog.2013.06.019

as the widespread use of epidural anal-gesia, may affect labor progress.7

Growing recognition for customizedcurves to fit specific situations, such asobese patients,9 may be warranted.Similarly, further understanding of laborprogress and risk factors for labor ab-normalities in twin gestations may helpproviders manage twin labor better andultimately decrease the rate of cesareandelivery. The purpose of this work was toinvestigate labor patterns of twin gesta-tions as compared with their singletoncounterparts, when controlling forimportant factors that may impact laborprogress.

MATERIALS AND METHODS

We identified a retrospective cohortfrom the electronic database created bythe Consortium on Safe Labor, reflectinglabor and delivery information from 12clinical centers (19 hospitals) and 9American College of Obstetricians andGynecologists (ACOG) US districts from2002-2008 (most from 2005-2007).6,8,10

This observational study was designedto study contemporary labor anddelivery practice across the country.It used 8 university affiliated hospitals,9 community teaching hospitals, and2 nonteaching hospitals, each selected by

FIGURE 1Eligibility criteria

Leftwich. Labor patterns of twins. Am J Obstet Gynecol 2013.

www.AJOG.org SMFM Papers

location, spanning the continentalUnited States, and availability of elec-tronic medical records. All births greaterthan 23 weeks were included in thisdatabase. Data extraction from the elec-tronic medical records was performedfrom each center for maternal de-mographics, complete medical, surgical,and obstetric history, as well as maternaland neonatal outcomes. Further detailsregarding this study are provided else-where.8 This project was approved by theinstitutional review board at all partici-pating institutions.

For our analysis, we included allwomen with twin gestations, cephalicpresentation of presenting twin, gesta-tional age�34 weeks, undergoing trial oflabor. We defined a trial of labor as agravida laboring with �2 cervical exam-inations. Exclusion criteria were presenceof fetal anomalies or fetal demise.Singleton controls were selected by thesame criteria. Maternal demographicvariables were extracted from the data-base for both the study group of twingestations and the control group of sin-gletons. Maternal demographic variablescollected included maternal age, gesta-tional age at delivery, body mass index,and race. Information regarding cervicalexaminations and labor were alsoextracted and included cervical dilationand effacement, number of cervical ex-aminations, induction or augmentationof labor, epidural usage, prior cesareandeliveries, and prior cesarean for failureto progress. Birthweight of singleton andthe presenting twin was also extractedand included for analysis.

Categorical variables were analyzed byc2 and continuous by the Student t test.Interval censored regression analysis wasused to determine distribution of timesto progress from 1 integer of cervicaldilation in centimeters to the next,assuming log normal distribution, toestimate the duration of active phaselabor. This centimeter by centimeter es-timate of cervical dilation in labor wasextrapolated from cervical examinationson admission and those subsequent ex-aminations performed in labor. If 2or more cervical examinations wereavailable the data were included in thiscentimeter estimate, regardless of

whether full dilation was reached or themode of delivery. These “traverse times”were calculated as median and 95thpercentiles. The median traverse timeswere then controlled for confoundingfactors, including birthweight of sin-gleton and presenting twin, maternalage, race, gestational age at delivery,prepregnancy body mass index (BMI),

SEPTEMBER 2013 Ameri

admission dilation, and rates of cesareandelivery. We used repeated-measuresanalysis with eighth degree polynomialmodel to construct mean labor curves byparity and number of fetuses for thosewho ultimately progressed to 10 centi-meters. This was done in the samefashion as Zhang et al6,8 with the curvesusing the starting point of time ¼ 0

can Journal of Obstetrics & Gynecology 254.e2

TABLE 1Maternal demographicsa

DemographicSingleton gestationb

(n [ 100,513)Twin gestationb

(n [ 891)

Maternal age, y 27.2 � 6.2 29.4 � 6.5

Gestational age, wks 39.1 � 1.5 36.5 � 1.5

Body mass index, kg/m2 25.1 � 6.0 26.0 � 6.8

Race

White 51.6 (49,297) 57.1 (481)

African American 23.5 (22,456) 27.0 (227)

Hispanic 16.8 (16,045) 11.2 (94)

Asian/Pacific Islander 5.0 (4808) 2.1 (18)

Other 3.0 (2872) 2.6 (22)

a All P < .01; b Data expressed as mean ± SD or % (n).

Leftwich. Labor patterns of twins. Am J Obstet Gynecol 2013.

SMFM Papers www.AJOG.org

when the dilation reached 10 cm and thetime calculated backward; after compu-tation the axis was reverted to a positivevalue. Therefore, only those gravidaswho reached full dilation, regardless ofthe delivery mode, were included in thelabor curve analysis. Labor curves wereconstructed beginning at 4 centimetersto reflect current practice of many in-stitutions not admitting patients untilgreater than 4 centimeters. P values werereported and statistical significance wasdefined as P < .05. SAS version 9.2 (SASInstitute, Cary, NC) was used foranalysis.

RESULTS

Of the total of 233,730 deliveriesreviewed for eligibility, a total of 891 twingestations met inclusion and exclusioncriteria and were compared with 100,513singleton controls (Figure 1). Table 1depicts the baseline characteristics oftwin and singleton gestations. Womenwith twin gestations were more oftenolder (29.4 � 6.5 vs 27.2 � 6.2 years),white or African American, had deliveryat earlier gestational age (36.5 � 1.5vs 39.1 � 1.5 weeks), and increasedprepregnancy BMI (26.0 � 6.8 vs25.1 � 6.0 kg/m2). There was an almost800 g greater birthweight in singletonscompared with the presenting twinswith mean weights 3326 � 477 and2567 � 401 g, respectively. Table 2

254.e3 American Journal of Obstetrics & Gynecol

compares labor and cervical examinationcharacteristics of both groups. Singletonspresented with more cervical dilation,however, there were no differences ineffacement or number of examinationsperformed in labor. Eighty percent ofsingleton and 71% of twin gravidas hadgreater than 4 cervical examinations. Ofnote, there were no differences in num-ber of prior cesarean deliveries, induc-tion, or augmentation of labor, orepidural use between the 2 groups.Whencomparing cesarean births, twin gesta-tions were almost twice as likely to havecesarean births (30.5% vs 16.1%); how-ever, they were statistically less likelyto be performed for failure to progress(P < .01).Labor progression was slower in the

nulliparous twin gestations, as notedby greater median traverse times atevery centimeter interval comparedwith singleton nulliparous pregnancies(Table 3), which continued to be the casewhen controlling for potentially con-founding factors (Table 4). Similarly formultiparas, significantly increased me-dian traverse times for twin gestationswere noted centimeter by centimeter upto 7 centimeters in the unadjusted ana-lyses (Table 3). From 7-10 cm, there weretoo few cervical examinations to evaluatemedian traverse times adequately, likelybecause of the rapid progress throughthese last few centimeters of dilation. A

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similar pattern was noted for multiparasin the adjusted analysis (Table 4). Laborcurves demonstrate this same delayedlabor progression for nulliparous twingestations compared with singletoncontrols (Figure 2); for example nullip-arous twins required 1 more hour thannulliparous singletons to complete thefirst stage of labor. There appears to be alack of inflection point in the nulliparoustwins, reflected also by their significantlylonger traverse times. Multiparous twinlabor curves revealed an even slower la-bor compared with multiparous single-tons requiring approximately 2-3 hoursmore to complete the first stage of labor.However, an inflection point was evidentfor multiparous laboring women, bothtwin and singletons, at approximately6.5 cm.

COMMENT

Our findings demonstrate that twingestations labor more slowly than theirsingleton counterparts. This observationremained true when controlling not onlybirthweight but other confounding fac-tors in both nulliparous andmultiparouswomen. This finding is especially perti-nent because the population of parturi-ents studied represents a contemporarygroup of women, similar to those pa-tients we currently care for on a day today basis.

When evaluating previous work onlabor progression in singleton vs twingestations, the literature is sparse andcontradictory. In support of our find-ings, Silver et al11 noted that twin activephase labor progressed slower thantheir singleton counterparts. Thisretrospective study was performed toevaluate labor in triplets gestations andcomparing them with labor in twin andsingleton gestations. They evaluated atotal of 64 twin gestations matched tocontrols for gestational age, parity, andepidural use.11 They showed twin activephase dilation proceeds at a slower rate,1.7 cm/hr vs 2.3 cm/hr in their singletoncounterparts, estimating approximately3.5 hours to progress from 4-10 centi-meters; however, less than our mediantraverse time of 9.7 hours. Friedmanalso concurred with these findings ina later investigation of 184 twin

TABLE 2Labor characteristics

CharacteristicSingleton gestation(n [ 100,513)a

Twin gestation(n [ 891)a P value

Induction 39.8 (38,795) 40.9 (355) .53

Augmentation 31.7 (22,423) 28.3 (172) .08

Epidural use 79.6 (51,826) 82.2 (462) .13

Cervical dilation, cm 3.7 � 2.4 3.3 � 2.2 < .01

Cervical effacement 75.3 � 4.1 75.2 � 23.3 .95

Number of cervical examinations 7.1 � 3.2 6.9 � 3.6 .13

Prior CD 6.2 (5804) 7.3 (60) .19

CD 16.1 (16,166) 30.5 (272) < .01

Failure to progress as indication for CD 47.5 (7683) 25 (68) < .01

Neonatal birthweight, g 3326 � 477 2567 � 401 < .01

CD, cesarean delivery.

a Data expressed as mean ± SD or % (n).

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gestations from 1956-1960, document-ing shortened latent phase and length-ened active and second stage.12 Hehypothesized that the shortened latentphase was secondary to the greaterprelabor dilatation identified in his twinpopulation. Of note, our twin gestationcohort had significantly less cervicaldilation on admission but our con-clusions remained similar in the activefirst stage of labor. Interestingly in

TABLE 3Unadjusted duration of labor, singlet

Cervicaldilation, cm

Nulliparas

Singletongestationa

Twingestationa

Pv

3-4 4.8 (10.6) 6.0 (11.9) <

4-5 3.5 (8.4) 3.8 (8.6) <

5-6 2.4 (5.9) 2.7 (6.2) <

6-7 1.7 (4.0) 1.8 (4.1) <

7-8 1.3 (3.0) 1.5 (3.2) <

8-9 1.2 (2.6) 1.3 (2.7) <

9-10 1.2 (2.6) 1.3 (2.8) <

4-10 8.8 (18.0) 10.7 (20.0) <

Validity of the model fit is questionable.

a Data expressed as median (95%); b Results shown are based

Leftwich. Labor patterns of twins. Am J Obstet Gynecol 201

our work multiparous twin gestationshad similar inflection points in activelabor to multiparous singleton gesta-tions as noted by Zhang et al,8 althoughnulliparous twins and singletons didnot.In contrast to our findings, Schiff

et al13 retrospectively reviewed 163 termtwin gestations in spontaneous laborand found that twin gestations hada significantly shorter first stage of

on vs twin gestation (h)

Multiparas

alueSingletongestationa

Twingestationa

Pvalue

.01 5.8 (12.3) 7.7 (14.2) < .01

.01 3.5 (8.1) 4.4 (9.1) < .01

.01 2.2 (5.6) 2.6 (6.0) < .01

.01 1.5 (4.2) 1.6 (4.3) < .01

.01 1.1 (3.0) 1.1 (3.1) eb

.01 1.0 (2.6) 1.0 (2.7) eb

.01 0.9 (2.3) 0.9 (2.3) eb

.01 8.2 (17.4) 9.7 (18.9) < .01

on the last maximum likelihood iteration.

3.

SEPTEMBER 2013 Ameri

labor compared with their matchedsingleton control gestations. Thesewomen delivered from 1984-1996,similar in time to Silver et al,11 butmany exclusion criteria resulted in atwin population quite different fromour twin cohort, excluding womenwith oxytocin augmentation, delivery<37 weeks, birthweight <2500 g,diabetes or hypertension and shortstature. To support these findings, theyhypothesized that shorter labor maybe a result of an overly distendeduterus contracting more effectivelythan a less distended singleton uterus.This is refuted by earlier work done byCaldeyro-Barcia and Poseiro14 whosework on the physiology of the uterinecontraction revealed that when theuterus is overstretched in cases ofpolyhydramnios, the uterine tone isabnormally elevated, however the in-tensity of contractions are decreased.As Silver et al examined a very smallsubset of twin deliveries and the abovehypothesized mechanisms of longerlabor are unproven theories, we choseto reexamine the labor patterns oftwin gestations compared to single-tons, controlling not only for birth-weight but many other factorssuggested to affect labor progressionto adequately answer this specificquestion.

Our findings support the clinical sus-picion that labor progression in twingestations is prolonged compared withtheir singleton counterparts. Strengths ofour investigation include the large num-ber of twin gestations studied as our workincluded over 3 times more twin gesta-tions than any of the aforementioned twinstudies. Furthermore, in our study, wecontrolled not only for birthweight butalso many other factors that may alterlabor progression. In addition, this studywas based on a modern population, rep-resenting women across the country whowere older, had larger BMI, increasedepidural and oxytocin use in comparisonto studies done by Friedman 50 years ago.We also had fewer exclusion criteria,making these findingsmore generalizable.

We recognize limitations of our studyincluding the use of a database designed

can Journal of Obstetrics & Gynecology 254.e4

TABLE 4Adjusted duration of labor, singleton vs twin gestation (h)a

Cervicaldilation, cm

Nulliparas Multiparas

Singletongestationb

Twingestationb

Pvalue

Singletongestationb

Twingestationb

Pvalue

3-4 5.2 (11.2) 6.4 (12.3) < .01 7.6 (14.4) 9.5 (16.2) < .01

4-5 3.8 (8.9) 4.4 (9.5) < .01 4.2 (9.2) 5.6 (10.6) < .01

5-6 2.6 (6.4) 3.3 (7.1) < .01 2.5 (6.3) 2.8 (6.6) .07

6-7 1.8 (4.3) 2.1 (4.6) < .01 1.7 (4.6) 2.0 (4.9) .30

7-8 1.4 (3.2) 1.6 (3.4) < .01 1.3 (3.5) 1.5 (3.7) .90

8-9 1.3 (2.8) 1.5 (3.0) < .01 1.1 (2.9) 1.2 (3.0) .06

9-10 1.4 (2.9) 1.6 (3.2) < .01 1.0 (2.6) 1.1 (2.8) < .01

4-10 9.6 (18.4) 12.7 (21.5) < .01 10.0 (18.7) 12.4 (21.2) < .01a Data adjusted for birthweight of singleton and presenting twin, maternal age, race, gestational age at delivery, prepregnancybody mass index, admission dilation, and cesarean delivery; b Data expressed as median (95%).

Leftwich. Labor patterns of twins. Am J Obstet Gynecol 2013.

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to answer a different research question;however, the Safe Labor project wascreated to evaluate labor in a contem-porary population, readily lending itselfto a secondary analysis of twin labor.Other limitations might include thesubjectivity of cervical examinations andthe lack of uniform labor protocols. It

FIGURE 2Labor curves for singleton and twin g

A comparison of labor curves for nulliparous and m

lines) gestations.

Leftwich. Labor patterns of twins. Am J Obstet Gynecol 2013.

254.e5 American Journal of Obstetrics & Gynecol

is also important to recognize the pos-sibility of selection bias, with providerchoice on management of labor for twingestations.The impact of our work in defining

longer duration of labor for twin gesta-tionsmay be in themanagement of thosetrying to achieve a vaginal delivery.

estations

ultiparous singleton (solid lines) and twin (dotted

ogy SEPTEMBER 2013

Ultimately, to adequately addresswhether implementation of this man-agement would decrease cesarean de-livery rates, a randomized controlledtrial should be performed. However,until then, in the active phase oflabor, allowing an additional 2-3 hoursfor nulliparous and multiparous twingestations could possibly lead to fewercesarean deliveries for failure toprogress. -

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