Predicting Incomplete Uterine Rupture With Vaginal.22[1]

8/6/2019 Predicting Incomplete Uterine Rupture With Vaginal.22[1]

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Predicting Incomplete Uterine Rupture With

Vaginal Sonography During the Late SecondTrimester in Women With Prior Cesarean

HIDEO GOTOH, MD, HIDEAKI MASUZAKI, MD, ATSUSHI YOSHIDA, MD,

SHUICHIRO YOSHIMURA, MD, TSUNETAKE MIYAMURA, MD, AND

TADAYUKI ISHIMARU, MD, PhD

Objective: To evaluate the usefulness of serial transvaginal

ultrasonographic measurement of the thickness of the lower

uterine segment in the late second trimester for predicting

the risk of intrapartum incomplete uterine rupture in

women with previous cesarean delivery.

Methods: Serial transvaginal ultrasonography with full

bladder was performed in 374 women without previous cesar-

ean delivery (control group) and 348 women with previous

cesarean delivery (cesarean group) from 19 to 39 weeks gesta-

tion. The thickness of the lower uterine segment was measured

in the longitudinal plane of the cervical canal.

Results: The thickness of the lower uterine segment de-

creased from 6.7 2.4 mm (mean standard deviation [SD]) at

19 weeks gestation to 3.0 0.7 mm at 39 weeks gestation in

the control group, but the thickness was more than 2.0 mm

throughout this period in each control subject. In the cesareangroup, the thickness decreased from 6.8 2.3 mm at 19 weeks

to 2.1 0.7 mm at 39 weeks gestation and was significantly

thinner than that of the control group after 27 weeks gestation

(P


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measurements) with previous cesarean delivery (cesar-ean group). Only a single measurement was made foreach fetus. Between January 1995 and December 1998,722 women were examined prospectively by transvag-inal ultrasonography between 19 and 39 weeks gesta-tion to measure the thickness of the lower uterinesegment and to detect the presence of any uterine defectwith a full bladder. All mothers were healthy, withuncomplicated singleton pregnancies. Patients repre-sented all women with uncomplicated pregnancies whoattended the antenatal clinic at our department within

the above time periods. None of the patients reported inthis study attempted vaginal birth after cesarean(VBAC).

The thickness of the lower uterine segment wasmeasured after the bladder was identified in the longi-tudinal plane of the cervical canal at transvaginal ultra-sonography (Figure 1). Ultrasonography was per-formed by using Mochida equipment with a 7.5-MHztransvaginal transducer (Sonovista Ex model meu-1581,Mochida, Japan). This system provides clear freeze-frames and the use of on-screen calipers for directmeasurements. All subjects were delivered after 37

weeks gestation. Measurement of the lower uterinesegment was repeated at least three times in eachexamination, and the minimal value was reported (to-tal: 722 measurements; control: 374; cesarean delivery:348). Intraobserver and interobserver variabilities in thecalculation of the thickness of the lower uterine seg-ment obtained for the first 50 women in the controlgroup were 4.7% and 5.5%, respectively. The sonogra-phers were masked to the type of patient (controlcompared with cesarean) to eliminate any possible bias.

Sonographic results at antepartum were comparedwith direct intraoperative observation at cesarean de-livery. Incomplete uterine rupture represented separa-tion of the uterine wall and visceral peritoneum cover-ing the uterus.11 We examined differences in thethickness of the lower uterine segment between controlpregnant women and those with previous cesarean

delivery at each gestational week, as well as the patternof change in the lower uterine segment during preg-nancy in each group. We also used the antenatal andintraoperative data to examine whether incompleteuterine rupture during delivery could be predictedfrom lower uterine segment measurement during preg-nancy. The surgeons were masked to the sonographicfindings at the time of cesarean delivery.

The study protocol was approved by the EthicsReview Committee of our institution, and a signedconsent form was obtained from each subject. Datawere expressed as mean standard deviation (SD), ormedian and range. Student t test and Mann-Whitney Utest were used for comparison of continuous variables.Differences in uterine thickness between control groupand cesarean group were evaluated by unpaired t test,and those between the second and third trimesters wereevaluated by paired t test. Fisher exact test was used toexamine the association between ultrasonographicallydetermined thickness of the lower uterine segment atdifferent stages of pregnancy and incomplete uterinerupture at the time of cesarean. Significance was con-sidered P .05. The sample size was sufficient to detectdifferences at 5% level of significance with 80% power.

Results

Patients in the cesarean group did not differ signifi-cantly from those in the control group with respect tomaternal age, parity, gestational age at delivery, infant

birth weight, and 1-minute and 5-minute Apgar scores(Table 1). The thickness of the lower uterine segment inthe control group decreased steadily from 6.7 2.4 mmat 19 weeks gestation to 3.0 0.7 mm at 39 weeksgestation, but the thickness was greater than 2.0 mm inall cases (Figure 2). In the cesarean group, the thicknessof the lower uterine segment decreased from 6.8

2.3 mm at 19 weeks gestation to 2.1 0.7 mm at 39weeks gestation (Figure 2). Whereas the thickness ofthe lower uterine segment was not different betweenthe two groups at 1926 weeks and 28 weeks gesta-tion, it was significantly thinner in the cesarean than inthe control group at 27 weeks and every week after 29weeks gestation (P .05). Serial measurements of thelower uterine segment during pregnancy showed thatin a subgroup of women with previous cesarean deliv-ery, the uterine wall was persistently thin from the

Figure 1. Transvaginal ultrasonography showing the lower uterine

segment and bladder full. Open arrow indicates uterine wall; solid arrow

indicates bladder wall.

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second trimester until the termination of pregnancy(thin group: lower uterine segment was less thanmean 1 SD, n 12, Figure 3). In another group of

women with previous cesarean delivery, the uterinewall decreased in thickness progressively, in a mannersimilar to that of the control group (nonthin group:lower uterine segment was mean 1 SD or greater, n27, Figure 3). Eleven of the 12 women (91%) with alower uterine segment less than the mean control 1SD in the late second trimester had a surprisingly verythin uterine wall at cesarean delivery; the fetal hair wasvisible through the amniotic membrane. In all 27women with lower uterine segment greater than themean control 1 SD, an intrapartum incomplete uter-

ine rupture at cesarean delivery did not develop (non-

thin group, P .001, Table 2).

Further analysis of transvaginal ultrasonographic

findings at 7 days before cesarean delivery (4 3 days)

and those at cesarean delivery showed that 17 of 23

women (74%) with lower uterine segment less than

2.0 mm before repeat cesarean delivery had an incom-

plete uterine rupture at cesarean delivery. On the other

hand, none of the 45 women with lower uterine seg-

ment of 2.0 mm or greater thickness demonstrated an

incomplete uterine rupture at cesarean delivery (P

.001, Table 2).

Figure 2. The mean thickness of the lower uterine segment in controls

and women who have had a previous cesarean delivery. The thickness

of the lower uterine segment was not different between the two groups

at 1926 weeks and 28 weeks gestation (*). The lower uterine segment

was significantly thinner in the cesarean group than in the control

group at 27 weeks and 29 weeks gestation (P .05, unpaired t test)

(**). The lower uterine segment was significantly thinner in the

cesarean group than in the control group at every week after 30 weeks

gestation (P .01, unpaired t test) (***). SD standard deviation.

Figure 3. Correlation between thickness of the lower uterine segment

at late second trimester and third trimester in the thin group and the

nonthin group. Note that in subjects in whom the lower uterine

segment was thin from the late second trimester, intrapartum incom-

plete uterine rupture was more likely to develop. NS not significant.

Table 1. Characteristics of Controls and Women WithPrevious Cesarean Delivery

Control Cesarean P

n 374 348

Maternal age (y) 28.9 5.3 31.9 4.6 NS*

Parity 1.9 0.9 1.4 0.8 NS*

Gestational age at

delivery (wk)

38.9 1.5 38.2 1.2 NS*

Birth weight (g) 3121 458 2953 483 NS*Apgar score 1-min 9 (8 10) 8 (710) NS

Apgar score 5-min 9 (8 10) 9 (8 10) NS

NS not significant.Data are presented as mean standard deviation, or median

(range).* Student t test. Mann-Whitney U test.

Table 2. Association Between UltrasonographicallyDetermined Thickness of the Lower UterineSegment at Different Stages of Pregnancy andIntrapartum Incomplete Uterine Rupture atCesarean

Thickness of lower uterine

segment(mm)

Intrapartum incomplete

uterine rupture

Yes(%) No (%)

At second trimester

Mean control 1 SD 11 (91) 1 (9)

Mean control 1 SD 0 (0) 27 (100)

Within 7 d (4 3 d) of

cesarean

2 mm 17 (74) 6 (26)

2 mm 0 (0) 45 (100)

SD standard deviation.(At second trimester and within 7 d of cesarean: P .001).

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Discussion

In 1988, ACOG recommended that carefully selected

patients be encouraged to have a trial of labor after a

single previous cesarean delivery.19 Several investiga-

tors have emphasized the efficacy and safety of vaginal

birth after cesarean delivery in a large series of stud-

ies.20,21 The most common complication of vaginal

delivery after a previous cesarean delivery is uterine

rupture, and the frequency varies between 0.5 to 0.8%

with previous lower uterine segment incision, as re-

ported in a recent study.22 Although maternal mortality

is rare, rupture of the uterus may be associated with

significant morbidity for the mother and fetus in

women with a history of low transverse cesarean deliv-

ery. Jones et al23 and Scott24 reported four perinatal

deaths among 20 cases of uterine rupture with a previ-

ous low-segment cesarean scar. Two of these infants

had long-term neurologic impairment, and three

women required hysterectomy.

Several investigators have examined the accuracy of

various diagnostic procedures in the detection of uter-ine rupture in women with previous cesarean delivery.Hysterography,12 pelvic examination,13 and amniogra-phy14 have been used, but their usefulness has not beenconfirmed. Hebisch et al25 compared the results ofultrasonography with those of magnetic resonance im-aging (MRI). They demonstrated that vaginal ultra-sonography provided more accurate information aboutthe condition of the scarred myometrium of the isthmusthan MRI. Other studies have shown that ultrasonogra-phy may predict uterine rupture in women with previ-

ous cesarean delivery. Rozenberg et al17 indicated thatthe risk of uterine rupture in the presence of a defectivescar was related directly to the degree of thinning of thelower uterine segment as measured by transabdominalultrasonography at or near 37 weeks gestation. Inparticular, they demonstrated that this risk increasedsignificantly when the thickness was 3.5 mm or less.The use of this cutoff value showed an excellent sensi-tivity (88.0%) for ultrasonography, with a negativepredictive value of 99.3%. On the other hand, Fukuda etal18 examined 41 low-segment transverse cesarean de-livery scars by transperineal and transvaginal longitu-

dinal scans. A wall thickness of 2 mm or less wasconsidered a sign of poor healing. At operation, theymeasured the thickness of the lower uterine segment byophthalmic calipers just after incising the uterus and

before rupture of the membranes, and reported nofalse-positive or false-negative results when using ul-trasonography.

Our results showed that when the thickness mea-sured by transvaginal ultrasonography is less than2 mm within 1 week of delivery, the lower uterine

segment may show an incomplete uterine rupture. Thepositive and negative predictive values were 73.9% and100%, respectively. Furthermore, a thickness of lessthan the control mean-SD at the second trimester ishighly predictive of the development of incompleteuterine rupture at delivery. The positive and negativepredictive values were 91.7% and 100%, respectively. A

careful examination of our results showed that thepredictive value at full term was lower than that at thesecond trimester. This finding is probably due to furtherthinning of the lower uterine segment at term as thewall is stretched by the presenting part. Although thedefects of the lower uterine segment can be detected inthe second trimester, our results showed that the mostclinically useful information regarding the status of thelower uterine segment is obtained when ultrasonogra-phy is performed before 36 weeks gestation. Measure-ments obtained at that time avoid problems associatedwith engagement of the presenting part in the pelvis orthe physiologic reduction in the volume of amnioticfluid occurring at later stages of pregnancy. Previousstudies that examined the importance of detecting uter-ine rupture by ultrasonography emphasized the valueof such evaluation at term,17,18 but our study stressesthe importance of performing such measurement dur-ing the late second trimester. We showed that serialmeasurements of the lower uterine segment by trans-vaginal ultrasonography during the second trimestermight predict incomplete uterine rupture at term.

Although none of our cases with incomplete uterinerupture progressed to a complete uterine rupture dur-ing labor, incomplete uterine rupture represents a high

risk for complete uterine rupture because in some caseswith incomplete uterine rupture, uterine contents areseparated from the peritoneal cavity only by the vis-ceral peritoneum covering the uterus.

In women with previous cesarean delivery, uterinerupture may occur after labor even in those withlower-uterine segmental incision. Thus, early predictionof uterine rupture before the onset of labor should alsoreduce the frequency of uterine rupture after delivery.Transvaginal ultrasonography could therefore be con-sidered the standard diagnostic procedure that canpredict accurately intrapartum uterine rupture in

women with previous cesarean delivery. Our resultsemphasize the importance of measuring the uterine scarin the late second trimester in women with previouscesarean delivery.

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Address reprint requests to:

Hideo Gotoh, MDDepartment of Obstetrics and GynecologyNagasaki University School of Medicine1-7-1 SakamotomachiNagasaki, 852-8501

Japan

Received June 21, 1999.

Received in revised form October 5, 1999.Accepted October 15, 1999.

Copyright 2000 by The American College of Obstetricians and

Gynecologists. Published by Elsevier Science Inc.

600 Gotoh et al Measurement of Uterine Thickness Obstetrics & Gynecology

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Predicting Incomplete Uterine Rupture With Vaginal.22[1]