Friday, January 14, 2011

Studies on ultrasonographic measurement of the lower uterine segment

These are all of the studies I could find on the national medical studies database, http://www.pubmed.com/, related to the ultrasonographic measurement of the lower uterine segment on patients with a prior cesarean section and its success in predicting uterine rupture/safety of trial of labor.  If you are an information junkie like me, these might be helpful in your decision as to whether or not to discuss with your health care professional the possibility of having this measurement performed.

J Obstet Gynaecol Can. 2010 Apr;32(4):321-7.
Sonographic lower uterine segment thickness and risk of uterine scar defect: a systematic review.
Jastrow N, Chaillet N, Roberge S, Morency AM, Lacasse Y, Bujold E.
Department of Obstetrics and Gynaecology, Centre Hospitalier Universitaire Sainte-Justine, Faculty of Medicine, Université de Montréal, Montreal QC.

OBJECTIVE: To study the diagnostic accuracy of sonographic measurements of the lower uterine segment (LUS) thickness near term in predicting uterine scar defects in women with prior Caesarean section (CS).

DATA SOURCES: PubMed, Embase, and Cochrane Library (1965-2009).

METHODS OF STUDY SELECTION: Studies of populations of women with previous low transverse CS who underwent third-trimester evaluation of LUS thickness were selected. We retrieved articles in which number of patients, sensitivity, and specificity to predict a uterine scar defect were available.

DATA SYNTHESIS: Twelve eligible studies including 1834 women were identified. Uterine scar defect was reported in a total of 121 cases (6.6%). Seven studies examined the full LUS thickness only, four examined the myometrial layer specifically, and one examined both measurements. Weighted mean differences in LUS thickness and associated 95% confidence intervals between women with and without uterine scar defect were calculated. Summary receiver operating characteristic (SROC) analysis and summary diagnostic odds ratios (DOR) were used to evaluate and compare the area under the curve (AUC) and the association between LUS thickness and uterine scar defect. Women with a uterine scar defect had thinner full LUS and thinner myometrial layer (weighted mean difference of 0.98 mm; 95% CI 0.37 to 1.59, P = 0.002; and 1.13 mm; 95% CI 0.32 to 1.94 mm, P = 0.006, respectively). SROC analysis showed a stronger association between full LUS thickness and uterine scar defect (AUC: 0.84 +/- 0.03, P < 0.001) than between myometrial layer and scar defect (AUC: 0.75 +/- 0.05, P < 0.01). The optimal cut-off value varied from 2.0 to 3.5 mm for full LUS thickness and from 1.4 to 2.0 for myometrial layer.

CONCLUSION: Sonographic LUS thickness is a strong predictor for uterine scar defect in women with prior Caesarean section. However, because of the heterogeneity of the studies we analyzed, no ideal cut-off value can yet be recommended, which underlines the need for more standardized measurement techniques in future studies.

Arch Gynecol Obstet. 2010 Feb 10.
Sonographic assessment of lower uterine segment at term in women with previous cesarean delivery.
Kushtagi P, Garepalli S.
KMC Quarters Manipal University Campus, Manipal, 576104, India, pralhadkushtagi@hotmail.com.

OBJECTIVE: To correlate lower uterine segment (LUS) thickness measured by abdominal sonography at term pregnancy with that measured manually using caliper at cesarean delivery and to find out minimum LUS thickness indicative of its integrity in women with previous cesarean.

METHODS: In 106 women with previous cesarean delivery and 68 with unscarred uterus, abdominal sonographic assessment of LUS was carried out within a week of delivery. Sonographic measurements were correlated with manual measurement of lower flap of LUS using Vernier calipers in 96 of these women (64 with previous cesarean and 32 of unscarred uterus) who had elective cesarean delivery.

RESULTS: Sonographically determined LUS was thinner among women with previous cesarean delivery than in those without (4.58 SD 1.05 vs. 4.8 SD 0.8; t = 1.986; p = 0.04). Women with vaginal birth after cesarean had thicker LUS than women with repeat cesarean delivery (4.4 SD 0.97 vs. 4.48 SD 1.0). The findings were not influenced by engaged fetal head status or amount of bladder fullness. Directly measured LUS thickness using Vernier calipers before delivery of the baby confirmed ultrasound measurements, but showed smaller differences between them. There were eight cases with defective uterine scar at cesarean. LUS thickness at term of 3 mm provided 87.5% sensitivity and specificity, and was found to have negative predictive value of 98%. But in two of seven cases the actual LUS was not measurable despite sonographic measurement of 3 mm, and there were two records of scar dehiscence in those with 3 and 4 mm of LUS thickness.

CONCLUSION: LUS thickness of 3 mm measured by abdominal ultrasonography prior to delivery at term in women with previous cesarean is suggestive of stronger LUS but is not a reliable safeguard for trial of labor.

Am J Obstet Gynecol. 2009 Sep;201(3):320.e1-6.
Prediction of complete uterine rupture by sonographic evaluation of the lower uterine segment.
Bujold E, Jastrow N, Simoneau J, Brunet S, Gauthier RJ.
Department of Obstetrics and Gynaecology, Faculty of Medicine, Centre de recherche du Centre hospitalier universitaire de Québec, Université Laval, Québec, QC, Canada. emmanuel.bujold@crchul.ulaval.ca

OBJECTIVE: The purpose of this study was to establish the validity of sonographic evaluation of lower uterine segment (LUS) thickness for complete uterine rupture.

STUDY DESIGN: A prospective cohort study of women with previous cesarean delivery was conducted. LUS thickness (full thickness and myometrial thickness only) was measured between 35 and 38 weeks gestation, and the thinnest measurement was considered to be the dependent variable. Receiver operating curve analyses and logistic regression were used.

RESULTS: Two hundred thirty-six women were included in the study. Nine uterine scar defects (3 cases of complete rupture during a trial of labor and 6 cases of dehiscence) were reported. Receiver operating curve analyses showed that full thickness of <2.3 mm was the optimal cutoff for the prediction of uterine rupture (3/33 vs 0/92; P = .02). Full thickness was also identified as an independent predictor of uterine scar defect (odds ratio, 4.66; 95% confidence interval, 1.04-20.91)

CONCLUSION: Full LUS thickness of <2.3 mm is associated with a higher risk of complete uterine rupture.

Int J Gynaecol Obstet. 2009 Nov;107(2):140-2. Epub 2009 Aug 13.
Comparison of transabdominal versus transvaginal ultrasound to measure thickness of the lower uterine segment at term.
Marasinghe JP, Senanayake H, Randeniya C, Seneviratne HR, Arambepola C, Devlieger R.
University Obstetrics and Gynecology Unit, De Soyza Hospital for Women, Colombo, Sri Lanka. jeevanmarasinghe@yahoo.com

OBJECTIVE: To compare the accuracy of transvaginal (TVS) versus transabdominal (TAS) ultrasound to assess the thickness of the lower uterine segment (LUS).

METHODS: Eighty-three pregnant women admitted for an elective cesarean delivery were enrolled. LUS thickness was measured using both TVS and TAS prior to the cesarean. The actual thickness of the LUS was measured using a sterile metal ruler after the neonate had been delivered.

RESULTS: Seventeen women had unscarred uteri (20.1%); 41 had had one previous cesarean (49.4%); and 25 had had two previous cesareans (30.1%). Mean thickness of the LUS measured after delivery was 7.58+/-1.3 mm in unscarred uteri; 5.09+/-1.4 mm for one cesarean; and 3.92+/-1.1 mm for two cesareans (P<0.01). Actual thickness of the LUS showed a significant correlation with TVS among the total (r(s)=0.89); with unscarred uteri (r(s)=0.68); with 1 cesarean (r(s)=0.89); and 2 cesareans (r(s)=0.68), while with TAS the correlations were significant only with the total (r(s)=0.53) and 2 previous cesareans (r(s)=0.63) (P<0.01).

CONCLUSION: TVS is a more accurate method of assessing the thickness of the LUS compared with TAS.

Ultrasound Obstet Gynecol. 2009 Mar;33(3):301-6.
Lower uterine segment thickness measurement in pregnant women with previous Cesarean section: reliability analysis using two- and three-dimensional transabdominal and transvaginal ultrasound.
Martins WP, Barra DA, Gallarreta FM, Nastri CO, Filho FM.
Departamento de Ginecologia e Obstetrícia da Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo and Escola de Ultra-sonografia de Ribeirão Preto, Ribeirão Preto, São Paulo, Brazil. wpmartins@gmail.com

OBJECTIVE: To evaluate the reliability of two- and three-dimensional ultrasonographic measurement of the thickness of the lower uterine segment (LUS) in pregnant women by transvaginal and transabdominal approaches.

METHODS: This was a study of 30 pregnant women who had had at least one previous Cesarean section and were between 36 and 39 weeks' gestation, with singleton pregnancies in cephalic presentation. Sonographic examinations were performed by two observers using both 4-7-MHz transabdominal and 5-8-MHz transvaginal volumetric probes. LUS measurements were performed using two- and three-dimensional ultrasound, evaluating the entire LUS thickness transabdominally and the LUS muscular thickness transvaginally. Each observer measured the LUS four times by each method. Reliability was analyzed by comparing the mean of the absolute differences, the intraclass correlation coefficients, the 95% limits of agreement and the proportion of differences < 1 mm.

RESULTS: Transvaginal ultrasound provided greater reliability in LUS measurements than did transabdominal ultrasound. The use of three-dimensional ultrasound improved significantly the reliability of the LUS muscular thickness measurement obtained transvaginally.

CONCLUSIONS: Ultrasonographic measurement of the LUS muscular thickness transvaginally appears more reliable than does that of the entire LUS thickness transabdominally. The use of three-dimensional ultrasound should be considered to improve measurement reliability.

Gynecol Obstet Fertil. 2005 Dec;33(12):1003-8.
The counselling of patient with prior C-section.

Rozenberg P.
Departement de gynecologie-obstetrique, centre hospitalier de Poissy--Saint-Germain, universite Versailles-Saint-Quentin, France. prozenberg@chi-poissy-st-germain.fr

A trial of labor after prior cesarean delivery is associated with a greater perinatal risk than is elective repeated cesarean delivery without labor, although absolute risks are low. Information and counselling aim to estimate specific risks and to balance these risks according to individual factors. Therefore, the physician has to answer two questions: (i) which would be the probability of successful vaginal delivery? (ii) which would be the risk of uterine rupture with a trial of labor? The risk factors for failure of trial of labor are: increased maternal age, obesity, and fetal macrosomia. The risk factors for uterine rupture are: increased maternal age, postpartum fever after the previous cesarean delivery, short interdelivery interval, history of at least two previous cesarean deliveries, and a history of classical incision. Conversely, other factors are of good prognosis: a prior vaginal delivery and, particularly, a prior VBAC (Vaginal Birth After Caesarean) are associated with a higher rate of successful trial of labor compared with patients with no prior vaginal delivery; ultrasonographic measurement of the lower uterine segment thickness>3.5 mm has an excellent negative predictive value for the risk of uterine defect. Finally, the wish for additional pregnancies following a cesarean section must be considered as an argument in favour of a trial of labor after accounting for the increasing risks correlated with repeated elective cesarean deliveries.

J Obstet Gynaecol Can. 2005 Jul;27(7):674-81.
Sonographic measurement of the lower uterine segment thickness in women with previous caesarean section.
Cheung VY.
Department of Obstetrics and Gynaecology, North York General Hospital, Toronto, ON.

OBJECTIVES: To evaluate the accuracy of prenatal sonography in determining the lower uterine segment (LUS) thickness in women with previous Caesarean section and to assess the usefulness of measuring LUS thickness in predicting the risk of uterine rupture during a trial of vaginal birth.

METHODS: Sonographic examination was performed in 102 pregnant women with one or more previous Caesarean sections at between 36 and 38 weeks' gestation to assess the LUS thickness, which was defined as the shortest distance between the urinary bladder wall-myometrium interface and the myometrium/chorioamniotic membrane-amniotic fluid interface. Of the 102 women examined, 91 (89.2%) had transabdominal sonography only, and 11 (10.8%) had both transabdominal and transvaginal examinations. The sonographic measurements were correlated with the delivery outcome and the intraoperative LUS appearance.

RESULTS: The mean sonographic LUS thickness was 1.8 mm, standard deviation (SD) 1.1 mm. An intraoperatively diagnosed paper-thin or dehisced LUS, when compared with an LUS of normal thickness, had a significantly smaller sonographic LUS measurement (0.9 mm, SD 0.5 mm, vs. 2.0 mm, SD 0.8 mm, respectively; P < 0.0001). Two women had uterine dehiscence, both of whom had prenatal LUS thickness of < 1 mm. Thirty-two women (31.4%) had a successful vaginal delivery, with a mean LUS thickness of 1.9 mm, SD 1.5 mm; none had clinical uterine rupture. A sonographic LUS thickness of 1.5 mm had a sensitivity of 88.9%, a specificity of 59.5%, a positive predictive value of 32.0%, and a negative predictive value of 96.2% in predicting a paper-thin or dehisced LUS.

CONCLUSIONS: Sonography permits accurate assessment of the LUS thickness in women with previous Caesarean section and therefore can potentially be used to predict the risk of uterine rupture during trial of vaginal birth.

Int J Gynaecol Obstet. 2004 Dec;87(3):215-9.
Ultrasonographic evaluation of lower uterine segment thickness in patients of previous cesarean section.
Sen S, Malik S, Salhan S. Department of Obstetrics and Gynecology, Vardhman Mahavir Medical College and Safdarjung Hospital, New Delhi, India. dr_sumana_sen@yahoo.com

OBJECTIVE: To evaluate by ultrasonography, the lower uterine segment thickness of women with a previous cesarean delivery and determine a critical thickness above which safe vaginal delivery is predictable.

METHODS: A prospective observational study of 71 antenatal women with previous cesarean delivery and 50 controls was carried out. Transabdominal and transvaginal ultrasonography were used in both groups to evaluate lower uterine segment thickness. The obstetric outcome in patients with successful vaginal birth and intraoperative findings in women undergoing cesarean delivery were correlated with lower segment thickness.

RESULTS: The overall vaginal birth after cesarean section (VBAC) was 46.5% and VBAC success rate was 63.5%, the incidence of dehiscence was 2.82%, and there were no uterine ruptures. There was a 96% correlation between transabdominal ultrasonography with magnification and transvaginal ultrasonography. The critical cutoff value for safe lower segment thickness, derived from the receiver operator characteristic curve, was 2.5 mm.

CONCLUSION: Ultrasonographic evaluation permits better assessment of the risk of scar complication intrapartum, and could allow for safer management of delivery.

J Ultrasound Med. 2004 Jul;23(7):907-11; quiz 913-4.
Second-trimester sonographic comparison of the lower uterine segment in pregnant women with and without a previous cesarean delivery.
Sambaziotis H, Conway C, Figueroa R, Elimian A, Garry D. Department of Obstetrics, Gynecology, and Reproductive Medicine, State University of New York Health Sciences Center at Stony Brook, Stony Brook, New York 11794, USA.

OBJECTIVE: To compare measurements of the lower uterine segment during a second-trimester sonographic examination in women with and without a previous cesarean delivery.

METHODS: Women undergoing second-trimester sonographic examination, 24 with a history of cesarean delivery and 30 control subjects with no history of cesarean delivery, were recruited for transvaginal sonographic evaluation of the lower uterine segment with a high-frequency probe. The uterine niche or previous cesarean scar site was defined as a small triangular anechoic defect in the anterior wall of the uterus. The uterine wall thickness was measured successively at the level where the bladder dome meets the lower uterine segment. Measurements were obtained with cursors at the interface of the urine-bladder and the amniotic fluid-decidua. The study was approved by the Institutional Review Board, and P < .05 was considered significant.

RESULTS: The uterine niche was identified in 14 (58%) of 24 women with a previous cesarean delivery. The lower uterine segment was significantly thinner in women with a previous cesarean delivery compared with control subjects (mean +/- SD, 4.7 +/- 1.1 versus 6.6 +/- 2.0 mm; P < .001). In the previous cesarean group, the mean lower uterine segment thickness was similar in the 5 women with 2 cesarean deliveries when compared with those with 1 cesarean delivery (4.6 +/- 1.0 versus 4.7 +/- 1.4 mm; P = .91). In a linear regression model, the only variable retaining significance in the prediction of uterine wall thickness was previous cesarean delivery (P= .002). Maternal age, parity, number of previous cesarean deliveries, and gestational age did not attain significance in the model.

CONCLUSIONS: The lower uterine segment during a second-trimester sonographic examination is significantly thinner in women with a previous cesarean delivery. Identification of the scar niche is possible in most of these women.

J Ultrasound Med 23:1441-1447 (2004)
Sonographic Evaluation of the Lower Uterine Segment in Patients With Previous Cesarean Delivery.
Cheung, V., Constantinescu, O., Ahluwalia, B. Department of Obstetrics and Gynecology, North York General Hospital, Toronto, Ontario, Canada (V.Y.T.C.); and BSA Diagnostic Imaging, Toronto, Ontario, Canada (O.C.C., B.S.A.), vcheung@nygh.on.ca.

Objective. To evaluate the appearance of the lower uterine segment (LUS) in pregnant women with previous cesarean delivery and to compare the LUS thickness with that in women with unscarred uteri.

Methods. In a prospective study, sonographic examination was performed on 53 pregnant women with previous cesarean delivery (cesarean group), 40 nulliparas (nullip-control), and 40 women who had 1 or more childbirths with unscarred uteri (multip-control) between 36 and 38 weeks’ gestation to assess the appearance and compare the thickness of the LUS. In the cesarean group, the sonographic findings were correlated with the delivery outcome and the intraoperative LUS appearance.

Results. In the cesarean group, 44 patients (83.0%) had a normal-appearing LUS indistinguishable from that of control groups; 2 patients (3.8%) had an LUS defect suggestive of dehiscence; and 7 patients (13.2%) had thickened areas of increased echogenicity with or without myometrial thinning. Although the cesarean group had a thinner LUS (1.9 ± 1.4 mm) when compared with both the nullip-control group (2.3 ± 1.1 mm; P > .05) and the multip-control group (3.4 ± 2.2 mm; P < .001), only the latter difference achieved statistical significance. One of the 2 patients who had a sonographically suspected LUS defect had confirmed uterine dehiscence during surgery. An intraoperatively diagnosed paper-thin LUS, when compared with an LUS of normal thickness, had significantly smaller sonographic LUS measurements (1.1 ± 0.6 versus 2.0 ± 0.8 mm, respectively; P = .004).

Conclusions. Prior cesarean delivery is associated with a sonographically thinner LUS when compared with those with prior vaginal delivery. Prenatal sonographic examination is potentially capable of diagnosing a uterine defect and determining the degree of LUS thinning in patients with previous cesarean delivery.

Aust N Z J Obstet Gynaecol. 2000 Nov;40(4):402-4.
Preoperative diagnosis of dehiscence of the lower uterine segment in patients with a single previous Caesarean section.

Suzuki S, Sawa R, Yoneyama Y, Asakura H, Araki T.
Department of Obstetrics and Gynecology, Nippon Medical School, Tokyo, Japan.

Preoperative diagnoses were checked during surgery in 39 patients who underwent elective repeat Caesarean section with (n = 20) and without (as control, n = 19) a preoperative diagnosis of wall dehiscence (thinning) of the lower uterine segment (LUS). All patients were examined manually and by ultrasonography at 36 weeks gestation before labour. A preoperative diagnosis of wall dehiscence was made when the wall thickness was less than 2 mm and/or the patient felt pain and tenderness in the LUS. Surgical findings of dehiscence were defined as a subperitoneal separation of the uterine scar in the LUS. The sensitivity and specificity of our ultrasonographic evaluations were found to be 100% and 83% (p < 0.05), respectively. On the other hand, there were no surgical findings of dehiscence in patients who felt pain and tenderness in the LUS with a wall thickness greater than 2 mm, nor among those in the control group.

J Nippon Med Sch. 2000 Oct;67(5):352-6.
Prediction of uterine dehiscence by measuring lower uterine segment thickness prior to the onset of labor: evaluation by transvaginal ultrasonography.
Asakura H, Nakai A, Ishikawa G, Suzuki S, Araki T. Department of Obstetrics and Gynecology, Nippon Medical School, Sedagi, Tokyo, Japan. asakura hirobumi@om.nms.ac.jp

OBJECTIVE: Lower uterine segment thickness was measured by transvaginal ultrasound examination and its correlations with the occurrence of uterine dehiscence and rupture was examined.

METHODS: The thickness of the muscular layer of the lower uterine segment was measured in 186 term gravidas with previous uterine scars and its correlation with uterine dehiscence/rupture was investigated.

RESULTS: Uterine dehiscence was found in 9 cases or 4.7%. There were no cases of the uterine rupture. The thickness of the lower uterine segment among the gravidas with dehiscence was significantly less in than those without dehiscence (p< 0.01). The cut-off value for the thickness of the lower uterine segment was 1.6 mm as calculated by the receiver operating characteristic curve. The sensitivity was 77.8%; specificity 88.6%; positive predictive value 25.9%; negative predictive value 98.7%.

CONCLUSION: Measurement of the lower uterine segment is useful in predicting the absence of dehiscence among gravidas with previous cesarean section. If the thickness of the lower uterine segment is more than 1.6 mm, the possibility of dehiscence during the subsequent trials of labor is very small.

Obstet Gynecol. 2000 Apr;95(4):596-600.
Predicting incomplete uterine rupture with vaginal sonography during the late second trimester in women with prior cesarean.
Gotoh H, Masuzaki H, Yoshida A, Yoshimura S, Miyamura T, Ishimaru T. Department of Obstetrics and Gynecology, Nagasaki University School of Medicine, Nagasaki, Japan.

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 cesarean delivery (control group) and 348 women with previous cesarean delivery (cesarean group) from 19 to 39 weeks' gestation. 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 decreased 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 cesarean group, 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 <.05). Eleven of 12 women (91%) with lower uterine segment less than the mean control - 1 SD in the late second trimester had a very thin lower uterine segment at cesarean delivery with fetal hair being visible through the amniotic membrane, ie, incomplete uterine rupture. In 17 of 23 women (74%) with lower uterine segment less than 2.0 mm in thickness within 1 week (4 +/- 3 days) before repeat cesarean delivery, intrapartum incomplete uterine rupture developed.

CONCLUSION: Transvaginal ultrasonography is useful for measurement of the uterine wall after previous cesarean delivery.

Eur J Obstet Gynecol Reprod Biol. 1999 Nov;87(1):39-45.
Thickness of the lower uterine segment: its influence in the management of patients with previous cesarean sections.
Rozenberg P, Goffinet F, Philippe HJ, Nisand I. Department of Gynecology and Obstetrics, Poissy Hospital, University Paris V, France. gynobs.poissy@wanadoo.fr

OBJECTIVE: To determine how ultrasound measurement of the lower uterine segment affects the decision about delivery for patients with previous cesarean sections (CS) and what are the consequences on cesarean section rates and uterine rupture or dehiscence.

PATIENTS: 198 patients: all women with a previous CS who gave birth in our department during 1995 and 1996 to an infant with a gestational age of at least 36 weeks and who underwent ultrasound measurement of their lower uterine segment (95-96 study group), compared with a similar population from 1989 to 1994 whose measurements were not provided to the treating obstetrician.

RESULTS: Among the patients with one previous CS, the vaginal delivery rate did not differ significantly during the two periods (70.3% for the 89-94 study period vs. 67.9% for the 95-96 study period, P=0.53), but the 95-96 study group experienced a significant increase in the rate of elective CS, compensated by a reduction in the rate of emergency CS (6.3% and 23.4%, respectively, for the 89-94 study period vs. 11.9% and 20.1% for the 95-96 study period, P=0.01). There was a very significant increase in the rate of vaginal delivery for the 95-96 study period among patients with two previous CS (26.7% vs. 8.0% for the 89-95 study period, P=0.01). The lower uterine segment was significantly thicker among women with a trial of labor than among those with an elective CS (4.5+/-1.4 mm compared with 3.8 +/- 1.5 mm; P=0.006); and the trial of labor group contained significantly fewer women with a lower uterine segment measurement less than 3.5 mm than did the elective CS group (24.0% compared with 56.6%; P<0.001). Two patients (0.8%) were found to have a defect of the uterine scar, a rate significantly lower than that observed in the early group (3.9%, P=0.03).

CONCLUSIONS: Ultrasound measurement of the lower uterine segment can increase the safe use of trial of labor, because it provides an additional element for assessing the risk of uterine rupture.

Minerva Ginecol. 1999 Apr;51(4):107-12.
Transvaginal ultrasonic evaluation of the thickness of the section of the uterine wall in previous cesarean sections.
Montanari L, Alfei A, Drovanti A, Lepadatu C, Lorenzi D, Facchini D, Iervasi MT, Sampaolo P.
Istituto di Clinica Ostetrica e Ginecologica, Universita degli Studi, IRCCS San Matteo, Pavia, Italy.

BACKGROUND: The aim of this study is to evaluate accuracy of transvaginal sonographic examination of the lower uterine segment in pregnant women with previous cesarean section.

METHODS: Sixty-one pregnant women between 37 and 40 weeks of gestation, with previous cesarean section underwent transvaginal ultrasonography. Wall thickness of the lower uterine segment, the length of cervix, dilation of the isthmus uteri were measured. On the basis of the surgical findings (in 53 patients) and outcome of the trial of labor (in 8 patients) a Score was assigned to the pregnant women: Score 1 to the women who had good healing or a trial of labor without complications; Score 2 to the women with a thin or discontinued scar and in case of threatened rupture of the uterus in the trial of labor.

RESULTS: The mean thickness of the lower uterine segment is 3.82 mm +/- 0.99 mm. The Score 1 group shows a mean thickness of 4.2 mm +/- 2.5 mm, and the Score 2 group a mean thickness of 2.8 mm +/- 1.06 mm. The transvaginal sonographic examination provides a sensitivity and a specificity respectively of 100 and 75%, for a thickness cut-off of 3.5 mm, and a positive and negative predictive values of 60.7% and 100% respectively.

CONCLUSIONS: The transvaginal sonographic evaluation of the lower uterine segment improves therefore the obstetrical decision-making regarding the trial of labor in women with previous cesarean section.

Tohoku J Exp Med. 1997 Sep;183(1):55-65.
Ultrasonographic evaluation of lower uterine segment to predict the integrity and quality of cesarean scar during pregnancy: a prospective study.
Qureshi B, Inafuku K, Oshima K, Masamoto H, Kanazawa K.
Department of Obstetrics and Gynecology, School of Medicine, University of the Ryukyus, Okinawa, Japan.

A prospective randomized study was conducted to measure the serial thickness of the lower uterine segment (LUS) by transvaginal ultrasonography in a control group of 80 women having no history of uterine surgery and in a study group of 43 women having a history of previous cesarean section (C/S). In the study group, more than 2 mm of thickness of the LUS was considered as good healing and less than 2 mm of thickness as poor healing. After serial sonographic examination, the women with good healing were given trial for labor unless an obstetrical indication for C/S existed. The appearance of the LUS during surgery was compared with antenatal ultrasonographic assessment by direct inspection. Twenty two (79%) of 28 women with a well healed scar had trial labor with the result that 46% had a successful vaginal birth without any uterine rupture of dehiscence. Eight women with poor healing all had elective C/S. Seven women with a 2 mm LUS thickness were individually categorized for delivery mode. Two of those women delivered vaginally. The LUS was found to be thin to translucent in these later two groups. Two mm or less as a criterion for poor healing had the sensitivity and specificity of 86.7% and 100% respectively. The positive predictive value was 100% and the negative predictive value was 86.7%. Ultrasonographic evaluation is effective in predicting the quality of a uterine scar and in differentiating the risk group of probable uterine rupture from the non risk group.

J Clin Ultrasound. 1996 Sep;24(7):355-7.
Sonographic evaluation of the wall thickness of the lower uterine segment in patients with previous cesarean section.

Tanik A, Ustun C, Cil E, Arslan A.
Radiology Department, 19 Mayis University, Samsun, Turkey.

In pregnant women with a history of cesarean section, wall thickness of the lower uterine segment may help determine the risk and safety of vaginal delivery. Determination of wall thickness may help identify the potential risk of uterine rupture in pregnant women who do not wish to have another cesarean section or who are not eligible for surgery due to other systemic disorders. In this study, 50 pregnant women with previous cesarean sections were evaluated with ultrasound preoperatively, and measurements of the lower uterine segment wall thickness were compared with intraoperative assessment of uterine thinning. These findings correlated highly with each other (sensitivity: 100%; specificity: 82% positive predictive value: 87%; negative predictive value: 100%), suggesting the reliability and safety of ultrasound in evaluating uterine wall thickness.

Zhonghua Fu Chan Ke Za Zhi. 1994 Aug;29(8):458-60, 508-9.
Detection of uterine scar defect during pregnancy by ultrasonics.
Yang TZ, Li WZ.
Second Affiliated Hospital, West China University of Medical Science, Chengdu.

B type ultrasonography was used to observe the formation of lower uterine segment in 71 primigravide and the status of lower uterine segment scar in 31 multiparae with previous cesarean section (CS), from the 33 to 41 gestational week. Results showed that the lower uterine segments was formed in all 102 cases after the 33rd week. Compared with the primigravide, the lower uterine segment in the CS group was longer, thinner and not as wide after the 37th gestational week. Defective scars of the lower uterine segment were found in 7 cases of the CS group and 2 of them were diagnosed as threatened dehiscence owing to the fetal sac protruding from the scar site. Condition of all these cases were confirmed during operation. The present study suggested that B ultrasonic scar can be a helpful and noninvasive method for detecting scar defect in the lower uterine segment following CS.

Lancet. 1996 Feb 3;347(8997):281-4.
Ultrasonographic measurement of lower uterine segment to assess risk of defects of scarred uterus.

Rozenberg P, Goffinet F, Phillippe HJ, Nisand I.
Department of Obstetrics and Gynaecology, Centre Hospitalier Intercommunal, Leon Touhladjian, Poissy, France.

BACKGROUND: Ultrasonography has been used to examine the scarred uterus in women who have had previous caesarean sections in an attempt to assess the risk of rupture of the scar during subsequent labour. The predictive value of such measurements has not been adequately assessed, however. We aimed to evaluate the usefulness of sonographic measurement of the lower uterine segment before labour in predicting the risk of intrapartum uterine rupture.

METHODS: In this prospective observational study, the obstetricians were not told the ultrasonographic findings and did not use them to make decisions about type of delivery. Eligible patients were those with previous caesarean sections booked for delivery at our hospital. 642 patients underwent ultrasound examination at 36-38 weeks' gestation, and were allocated to four groups according to the thickness of the lower uterine segment. Ultrasonographic findings were compared with those of physical examination at delivery.

FINDINGS: The overall frequency of defective scars was 4.0% (15 ruptures, 10 dehiscences). The frequency of defects rose as the thickness of the lower uterine segment decreased: there were no defects among 278 women with measurements greater than 4.5 mm, three (2%) among 177 women with values of 3.6-4.5 mm, 14 (10%) among 136 women with values of 2.6-3.5 mm, and eight (16%) among 51 women with values of 1.6-2.5 mm. With a cut-off value of 3.5 mm, the sensitivity of ultrasonographic measurement was 88.0%, the specificity 73.2%, positive predictive value 11.8%, and negative predictive value 99.3%.

INTERPRETATION: Our results show that the risk of a defective scar is directly related to the degree of thinning of the lower uterine segment at around 37 weeks of pregnancy. The high negative predictive value of the method may encourage obstetricians in hospitals where routine repeat elective caesarean is the norm to offer a trial of labour to patients with a thickness value of 3.5 mm or greater.

Arch Gynecol Obstet. 1991;248(3):129-38.
Ultrasound examination of caesarean section scars during pregnancy.

Fukuda M, Shimizu T, Ihara Y, Fukuda K, Natsuyama E, Mochizuki M.
Fukuda Ladies Clinic, Ako, Japan.

Two hundred and sixteen transverse caesarean section scars were examined sonographically near term by a conventional method (175 scars) and a new method (41 scars). The new method consisted of obtaining a transabdominal longitudinal scan by the conventional method and also by a 3M conductor, a transabdominal frontal scan to give a surface view of the scar, and transperineal and transvaginal longitudinal scans. The new method was used from 16 weeks of gestation onwards. Of 41 scars scanned by the new method, 31 showed good healing, being more than 2 mm in thickness throughout; 10 scars showed poor healing with a thickness of less than 2 mm and loss of continuity. Of 31 patients with good healing, 8 delivered vaginally and the remaining 23 patients had repeat caesarean sections for other obstetric indications. All patients with ultrasound evidence of poor healing had repeat caesarean sections. At operation the thickness of the lower uterine segment was measured with ophthalmic calipers. There were 4 false negative results (4/83: 4.8%) and 1 false positive result (1/43: 2.3%) with conventional ultrasound and no false positives or false negatives with the new method.

Arch Gynecol Obstet. 1988;243(4):221-4.
Examination of previous caesarean section scars by ultrasound.

Fukuda M, Fukuda K, Mochizuki M.
Fukuda Ladies Clinic, Ako, Japan.

We examined 84 lower segment caesarean section scars by ultrasonography near term. Seventy scars showed good healing with a thickness of the lower uterine segment of more than 3 mm; 14 scars showed poor healing with a thickness of less than 2 mm and loss of continuity. Among 70 patients with good healing, 24 patients delivered vaginally but the remaining 46 patients have had repeat caesarean sections for other obstetric indications. Intraoperative findings in these 46 patients were as follows: Grade I (no thinning of the lower uterine segment), 42; Grade II (thinning and loss of continuity of the lower uterine segment but fetal hair not visible), 4; Grade III (thinning of the lower uterine segment and fetal hair visible), 0. Fourteen patients with poor healing had repeat caesarean sections. Intraoperative findings in these 14 patients were as follows: Grade I, 0; Grade II, 9; Grade III, 5. These results indicate that ultrasound examination detect thinning of the lower uterine segment and may help to determine management.

Obstet Gynecol. 1988 Jan;71(1):112-20.
Ultrasound diagnosis of defects in the scarred lower uterine segment during pregnancy.

Michaels WH, Thompson HO, Boutt A, Schreiber FR, Michaels SL, Karo J.
Department of Obstetrics and Gynecology, Providence Hospital, Southfield, Michigan.

A prospective study was begun using ultrasound to diagnose defects in the lower uterine segment. Seventy patients were examined and delivered by cesarean section, including 58 at risk because of previous cesarean section and 12 nulliparous controls not at risk. Of the at-risk patients, 12 had confirmed defects, for an incidence of 20.7%. All the controls were normal. The false-positive rate for at-risk patients was 7.1%, and the positive and negative predictive values were 92.3 and 100%, respectively. For the diagnosed cases, the sonographic lower uterine segment seemed to form earlier (P less than .01) and was thinner (P less than .01) than that in the negative cases or the controls. Although our study design was observational and did not allow us to test the performance of the lower uterine segment when a defect was found, we discuss the use of a three-stage classification system to assist in identifying sonographically detected defects in a future trial of labor protocol. We conclude that sonographic surveillance is a reliable and practical means of evaluating the lower uterine segment after conception and before labor or delivery. 

1 comment:

Sapreena Lewis said...

Thanks for consolidating the results from various studies Leigha. Really helpful.