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Abstract Objective: To evaluate the effect of early am-niotomy in term gestation on the mode of delivery andpregnancy outcome in comparison with premature rup-

ture of membranes (PROM) and oxytocin induction.Study design: The study population consisted of 60 con-secutive parturients induced by early amniotomy. Thetwo comparison groups were 147 women admitted withterm PROM and 65 patients induced by oxytocin. Allstudy participants were evaluated prospectively and hadunfavorable cervical scores.Results: The duration of thefirst stage of labor was significantly longer in the PROMgroup (987.8572.3 min) as compared with the early am-niotomy group (615.0389.6 min) and the oxytocin in-duction group (650.9349.5 min,P


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Methods

Study population

The study population consisted of 60 consecutive parturients withterm gestations whose labor was induced by early amniotomy.They all delivered at the Soroka University Medical Center be-tween November 1, 1997 and January 30, 1998. The comparisongroups comprised of women who were admitted to the delivery

ward with term premature rupture of membranes (PROM,n=147),and the second comparison group were women whose labor wasinduced by oxytocin with intact membranes (n=65). All womendelivered during the same period of time. Early amniotomy wasdefined as artificial rupture of the membranes when the Bishopscores where less than 5. Term PROM was defined as rupture ofthe membranes six hours prior to commencement of spontaneousuterine contractions. Subjects were eligible if they met the follow-ing inclusion criteria: Bishop scores of less than 5, singleton ges-tations, vertex presentation, term delivery (>37 completed weeksof gestation). The exclusion criteria were parturients who requiredan immediate cesarean section because of maternal or fetal indica-tions, parturients who had a history of more than one cesarean sec-tion or a previous classical uterine scar.

Data

Data were collected prospectively and information was obtainedupon admission regarding demographic and obstetric characteris-tics including maternal age, gravity, parity, gestational age andoutcome of previous pregnancies (i. e. spontaneous delivery ver-sus cesarean section). The indications for induction of labor wererecorded as well.

Bishop scores were evaluated before induction of labor wasinitiated. While a cesarean section was performed, the indicationswere recorded. Information about labor duration, mode of deliv-ery, Apgar scores and birth weight were collected. The study wasapproved by the local ethics institutional review board.

Statistical analysis

The comparison of group means was performed using student t-test. Chi- square or Fisher exact tests were used for comparison ofproportions. P


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compared with the controls (11.6% among women fromthe PROM group and 16.9% in the oxytocin group).While calculating the risk for having a CS in the indexpregnancy, early amniotomy was found to carry a statis-tically significant higher risk for CS when compared

with the PROM group (OR=2.8; 95%CI 1.2, 6.3). Whilecomparing the risk for CS to the oxytocin group, a high-er although non statistically significant trend towards CSrates was found (OR= 1.8; 95% CI 0.7,4.5). Althoughthe 5 min Apgar scores were significantly lower in theearly amniotomy group as compared with the othergroups, the pH values were not significantly different.

The indications for CS are summarized in Table 4,and did not differ significantly between the groups, butthe numbers were too small to allow a significant com-parison. The main indication for CS was non-progressive1st stage of labor, followed by suspected fetal distressand suspected abruption placenta.

Because a previous CS increases the risk for havingsubsequent one [2, 17, 18], we performed a stratifiedanalysis comparing the risk of CS for parturients whohad a previous CS and for those who had not (Table 5).While the trend for higher CS, when comparing parturi-ents without a scarred uterus to the PROM group still re-mained, this trend was not observed when comparingthose patients with the oxytocin group. Only 5 patientsfrom the oxytocin group had a previous CS, and none ofthem had another one. The Mantel Haenszel weightedOR for having a CS in the PROM vs. early amniotomywas 0.49 with 95% CI of 0.21, 0.99. While comparing

oxytocin induction with early amniotomy in the stratifiedanalysis, the weighted OR was 0.72; 95% CI 0.26,1.96.

Discussion

The basis for the present study was the previous retro-spective study performed by our group [19] where earlyamniotomy was found to be associated with a signifi-cantly increased risk for CS. This study was conductedprospectively in order to obtain more detailed informa-tion about the course of labor which was not available inthe medical records (mainly the reasons for induction),and to investigate the independent contribution of earlyamniotomy to the poor outcome while comparing it withan additional method of induction among women withsimilar cervical scores. This study substantiated the find-ings of our previous research. Significantly higher rate ofCS was found in the early amniotomy group when com-pared with the PROM group. Comparing this group tothe oxytocin induction group lacked statistical power. In-deed, both groups of induction had a higher rate of CSthan the natural PROM. This trend is mainly due to thereasons that led to the induction that were quite similarin both groups (as shown in Table 1). Attempted induc-tion of labor has a risk for failure which thus results inCS [13].

Cesarean section is the most frequently performedmajor operation in the United States, where about onemillion such operations are performed each year [13].

Table 3 Labor characteristicsand neonatal outcome in thestudy groups

Variable Early PROM Oxytocin P ValueAmniotomy (n=147) Induction(n=60) (n=65)

Bishop score 3.31.5 3.31.1 3.31.5 NS

Administration of oxytocin 15 (25.0%) 35 (23.8%) 65 (100%) NSCervical dilatation at initiation 1.51.9 1.31.5 1.71.7 NS

of oxytocin (meanSD)

Mode of deliveryPartus spontaneous 40 (66.7%) 124 (84.4%) 46 (70.8%) Vacuum extraction 4 (6.7%) 6 (4.1%) 8 (12.3%) CS 16 (26.7%) 17 (11.6%) 11 (16.9%) 0.012

Duration of labor (min SD)

1st stage 615.0389.6 987.8572.3 650.9349.5


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Cesarean birth rate has quadrupled in less than 2 decades[13], a trend that is worldwide [5, 7, 16]. Thus, the wide-ly increasing rate of CS is a major obstetric hazard.While Barrett et al. [4] found that early amniotomy re-duce the risk for CS, Carroll et al. [9] performed a meta-analysis study investigating the effect of amniotomy onpregnancy outcome which contradicted this conclusion.The meta-analysis included seven different trials, andconcluded that although early amniotomy is associatedwith a reduction in labor duration, there is a trend toward

an increase in the risk of cesarean delivery. Our studysupports both conclusions. The labor duration was sig-nificantly shorter in the two induction groups, as expect-ed when there is an active management of labor.

The reasons for the high rates of CS in our study arerelated to several factors, mainly the underlying condi-tions leading to the induction. These reasons (as summa-rized in Table 1) undoubtedly contribute to the CS rates.In addition, the presence of scarred uterus, which wassignificantly higher in the study group, also influencesthe trend for higher CS rates. Although vaginal birth isthe preferred course of action after one CS [11, 12], therisk for another CS is higher as compared to parturients

without a previous one [2, 17, 18]. Other factors includethe improvement of the preventative medicine allowingearly detection of problems, like the wide use of fetalheart rate monitoring, with its false positive alarm. Like-wise, the unfavorable cervical scores at initiation of in-duction might suggest that it is better to prepare the cer-vix before rupturing the membranes or using oxytocinintra venous.

This work is an observational prospective study thathas several limitations. The first of these is the lack ofrandomization resulting in differences in the characteris-tics of the three groups, potentially introducing bias. Themajor differences were higher parity, and higher rates ofprevious CS in the early amniotomy group. Parity couldbe a confounding factor as it increases the risk of havinghad a previous CS. However, the analysis presented inTable 5 adjusted for this factor. Both groups of inductioni. e. early amniotomy and oxytocin administration weresimilar in their indications for induction, in the gestatio-nal age, cervical scores and in many other variables ex-cept for the parity and the previous CS rates. This trendreflects the cautious use of oxytocin in patients with highparity or scarred uterus. Interestingly, while performingthe stratified analysis, early amniotomy was not found tocarry a higher risk for CS when compared with the oxy-

tocin, while controlling for a previous scar. Moreover,some of those patients were augmented with oxytocin.Thus, it seems that when the cervical scores are unfavor-able for labor, and the patient did not have a previousCS, both ways of induction are comparable.

The fetal outcome was similar in all groups. The sta-tistically significant lower Apgar scores in the studygroup do not have any significant clinical meaning aslong as those scores were above 7 [3]. Moreover, the pHvalues were similar in all groups.

In summary, early amniotomy is associated with ahigher rate of CS in comparison with PROM and oxyto-cin induction. While controlling for a previous CS itseems that both ways of induction, early amniotomy andoxytocin are comparable. In order to decrease the CSrates, after confirming the true need for induction, itshould probably start with cervical ripening techniquesin order to improve the Bishop scores. Further studiescomparing early amniotomy to other methods of induc-tion that improve the cervical scores, like vaginal PGE2,are required in order to isolate the contribution of thescore itself to the success of the induction.

References

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Table 5 Stratified analysis for the risk of CS by a previous CS (Data are given in OR and 95%CI)

Variable Early Amniotomy PROM Oxytocin Inductionn=60 n=147 n=65Reference OR (95%CI) OR (95%CI)

Risk for CS in patients without a previous CS 1 0.48 (0.16; 1.49) 1.19 (0.38; 3.8)Risk for CS in patients with a previous CS 1 0.52 (0.10; 2.70) Weighted OR 1 0.49 (0.21; 0.99) 0.73 (0.26; 1.96)

CScesarean section;OR odds ratio;CIconfidence interval


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