A couple weeks ago Virginia from Switzerland left this comment:
I am planning to have a vbac at a hospital in Geneva, Switzerland. In general, they are very supportive of vbacs here.
It is common practice here to measure the uterine scar at 37 weeks using a sonogram. Apparently, if the scar tissue is 3.5mm or higher – it is very unlikely for a rupture. Mine happens to be 2.95mm. The hospital staff tells me I have a 3 – 4% chance of a rupture versus a standard .05% chance of rupture. They warned me that I will be monitored heavily during the birth because of these factors. Do you know much about this theory or know where I can find more information about this?
Typically the rate of rupture quoted for a woman with one prior bikini cut cesarean is about half a percent or 0.5%. The thickness of the uterine scar/wall and it’s relation to rupture is something I’ve heard discussed quite a bit, but have never personally researched.
My lay opinion? Intuitively, this makes sense, but the studies we have are not strong enough to prove it. While it may seem reasonable to say, “The thicker the uterus, the less likely one is to rupture,” where we do draw the line at what is “thick enough?” There are several studies that focus on measuring uterine thickness via ultrasound on women with prior cesareans, ten of which are listed below, but none of them are large enough to make any definitive decisions.
When looking at something like uterine rupture that happens about half of a percent of the time, you need to include thousands of test subjects in order to get an accurate assessment of the frequency of the occurrence. We just don’t have that here. These are interesting preliminary studies that should be duplicated using thousands of women. If there is a way to accurately predict which scars will rupture, this is important information to have, but there is currently insufficient evidence available.
|No||Study||total # of women||# of women with prior cesarean||Notes|
|1||Rozenberg 1996||642||642||calculates rupture by uterine thickness|
|2||Cheung 2004||133||53||compares scarred (1.9 ± 1.4 mm), unscarred w/ 1st pg 2.3 ± 1.1 mm; P > .05 , and unscarred w/ 2nd or more pg (3.4 ± 2.2 mm; P < .001)|
|3||Gotoh 2000||722||348||compares scarred & unscarred|
|4||Sen 2004||121||71||compares scarred & unscarred|
|5||Qureshi 1997||43||43||calculates rupture by uterine thickness|
|6||Michaels 1998||70||58||compares scarred & unscarred|
|8||Montanari 1999||61||61||average thickness = 3.82 mm +/- 0.99 mm|
If you, like Virigina, are faced with a minimum uterine thickness standard, request the research your doctor cites and look it up.
If you know of a large study, please leave a comment below with the study citation.
For those who like to skim, I’ve bolded the most interesting parts of the abstracts.
More more information on the subject, check out Sonographic Measurement of the Lower Uterine Segment Thickness: Is it Truly Predictive of Uterine Rupture? by Vincent Y.T. Cheung, MBBS, FRCOG, FRCSC, Department of Obstetrics and Gynaecology, North York General Hospital, University of Toronto, Toronto ON. It was published in February 2008 and has a great bibliography.
|Lower uterine segment thickness||Number of cases||Number of ruptures|
|Greater than 4.5 mm||278||0|
|3.6 – 4.5 mm||177||3 (2%)|
|2.6 – 3.5 mm||136||14 (10%)|
|1.6 – 2.5 mm||51||8 (16%)|
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.
Vincent Y. T. Cheung, MBBS, FRCOG, FRCSC, RDMS, Oana C. Constantinescu, MD, RDMS and Birinder S. Ahluwalia, MBBS, RDMS. J Ultrasound Med 23:1441-1447 • 0278-4297. 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.).
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.
This is the most interesting study because it compares scarred uteri to unscarred uteri that are pregnant for the first time to unscarred uteri that are pregnant for at least the second time. I think this study is important because when creating a uterine thickness standard, it’s important to understand what is a “safe” thickness. How thick is an unscarred uterus in its first pregnancy and subsequent pregnancies? We can then compare this standard to unscarred uteri. It is fascinating that 83% of the scarred uteri were “indistinguishable” from the unscarred uteri. Since we are dealing with such small numbers here, 133 women total, it would be irresponsible to create a thickness standard based on this study alone. If this same study was performed on 10,000 women from each category, that would be a study whose findings would be powerful enough to rightfully influence VBAC policy.
Gotoh H, Masuzaki H, Yoshida A, Yoshimura S, Miyamura T, Ishimaru T. Obstet Gynecol. 2000 Apr;95(4):596-600. 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.
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.
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.
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.
Ultrasonographic evaluation permits better assessment of the risk of scar complication intrapartum, and could allow for safer management of delivery.
Qureshi B, Inafuku K, Oshima K, Masamoto H, Kanazawa K. Tohoku J Exp Med 1997 Sep;183(1):55-65. Department of Obstetrics and Gynecology, School of Medicine, University of the Ryukyus, Okinawa, Japan.
Table 4: Distribution of delivery mode by lower uterine segment thickness
Lower uterine segment thickness Number of cases Elective C/S Successful TOL Failed TOL Greater than 2 mm 28 6 (21.4%) 13 (46.4%) 9 (32.1%) Equal to 2mm 7 5 (42.9%) 2 (28.6%) 2 (28.6%) Less than 2 mm 8 8 (100%) 0 0 Total 43 17 (39.5%) 15 (34.9%) 11 (25.6%)
2 mm of thickness of the LUS was considered as good healing and less than 2 mm of thickness as poor healing…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.
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.
Rozenberg P, Goffinet F, Philippe HJ, Nisand I. Eur J Obstet Gynecol Reprod Biol 1999 Nov;87(1):39-45. Department of Gynecology and Obstetrics, Poissy Hospital, University Paris V, France. email@example.com
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. DESIGN: Prospective open study. 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. PMID: 10579615, UI: 20044216
I could not find the full article of this study, only the abstract, so I don’t know if the women were permitted to select their delivery mode or if it was determined by their uterine thickness.
Study #8: [Transvaginal ultrasonic evaluation of the thickness of the section of the uterine wall in previous cesarean sections]. [Article in Italian]
Montanari L, Alfei A, Drovanti A, Lepadatu C, Lorenzi D, Facchini D, Iervasi MT, Sampaolo P. Minerva Ginecol 1999 Apr;51(4):107-12. Istituto di Clinica Ostetrica e Ginecologica, Universita degli Studi, IRCCS San Matteo, Pavia.
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. PMID: 10379144, UI: 99307817
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.
Hirobumi Asakura, Akihito Nakai, Gen Ishikawa, Shyunji Suzuki and Tsutomu Araki. Journal of Nippon Medical School. Vol. 67 (2000) , No. 5 pp352-356. Department of Obstetrics and Gynecology, Nippon Medical School.
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.