Sonographic evaluation of the lower uterine segment in patients with previous cesarean delivery

The role of the lower uterine segment thickness in predicting preterm birth in twin pregnancies presenting with threatened preterm labor

OBJECTIVES

To examine the relationship between the lower uterine segment (LUS) thickness and the onset of labor in dichorionic twin pregnancies experiencing threatened preterm labor.

METHODS

This prospective cohort study included dichorionic twin pregnancies between 24 and 32 weeks of gestation, presenting with symptoms of preterm labor. The LUS thickness and mid-anterior wall thickness were measured via transabdominal ultrasonography, cervical length, and posterior cervical lip thickness were measured transvaginally. The presence of the cervical sliding sign and funneling findings were recorded.

RESULTS

Among the patients with an onset of labor before the 34th week, the mean LUS thickness was 3.8 ± 0.9 mm, compared to 4.6 ± 1.1 mm in those with an onset of labor at or after 340/7 GW, indicating a statistically significant difference (p=0.012). Similarly, accepting the GW threshold as 350/7 weeks, a statistically significant difference was found in the mean LUS thickness, which was 4.0 ± 1.0 mm in those with an earlier onset of labor and 4.7 ± 1.0 mm in those with a later onset of labor (p=0.022). While univariate analysis indicated that the LUS thickness was a significant predictor (p=0.017 for <34 GW and p=0.028 for <35 GW), multivariate analysis showed a reduced effect (p=0.04 and p=0.06, respectively).

CONCLUSIONS

LUS was significantly thinner in pregnancies with an onset of labor before the 34th and 35th GW. The measurement of the LUS thickness can be considered an alternative method for predicting spontaneous preterm birth in dichorionic twin pregnancies.

Uterine wound healing after caesarean section: A systematic review

The rate of caesarean section (CS) is increasing worldwide. Defects in uterine healing have a major gynaecological and obstetric impact (uterine rupture, caesarean scar defect, caesarean scar pregnancy, placenta accreta spectrum). The complex process of cellular uterine healing after surgery, and specifically after CS, remains poorly understood in contrast to skin wound healing. This literature review on uterine wound healing was mainly based on histological observations, particularly after CS. The primary objective of the review was to examine the effects of CS on uterine tissue at the cellular level, based on histological observations. The secondary objectives were to describe the biomechanical characteristics and the therapies used to improve scar tissue after CS. This review was performed using PRISMA criteria, and PubMed was the data source. The study included all clinical and animal model studies with CS and histological analysis of the uterine scar area (macroscopic, microscopic, immunohistochemical and biomechanical). Twenty studies were included: 10 human and 10 animal models. In total, 533 female humans and 511 female animals were included. Review articles, meeting abstracts, case series, case reports, and abstracts without access to full-text were excluded. The search was limited to studies published in English. No correlation was found between cutaneous and uterine healing. The histology of uterine scars is characterized by disorganized smooth muscle, fibrosis with collagen fibres and fewer endometrial glands. As for skin healing, the initial inflammation phase and mediation of some growth factors (particularly connective tissue growth factor, vascular endothelial growth factor, platelet-derived growth factor, tumour necrosis factor α and tumour necrosis factor β) seem to be essential. This initial phase has an impact on the subsequent phases of proliferation and maturation. Collagen appears to play a key role in the initial granulation tissue to replace the loss of substance. Subsequent maturation of the scar tissue is essential, with a decrease in collagen and smooth muscle restoration. Unlike skin, the glandular structure of uterine tissue could be responsible for the relatively high incidence of healing defects. Uterine scar defects after CS are characterized by an atrophic disorganized endometrium with atypia and a fibroblastic highly collagenic stromal reaction. Concerning immunohistochemistry, one study found a decrease in tumour necrosis factor β in uterine scar defects. No correlation was found between biomechanical characteristics (particularly uterine strength) and the presence of a collagenous scar after CS. Based on the findings of this review, an illustration of current understanding about uterine healing is provided. There is currently no validated prevention of caesarean scar defects. Various treatments to improve uterine healing after CS have been tested, and appeared to have good efficacy in animal studies: alpha lipoic acid, growth factors, collagen scaffolds and mesenchymal stem cells. Further prospective studies are needed.

[Usefulness of ultrasound measurement of the lower uterine segment before delivery of women with a prior cesarean: Literature review]

Identifying women with a history of cesarean delivery and at real risk for uterine rupture is an important aim in obstetric care. It is with this objective that different authors have evaluated the interest of ultrasound for predicting the risk of a cesarean scar defect by measuring the thickness of the lower uterine segment. The literature is sparse and subject to numerous biases because they are mainly prospective cohort studies with small numbers. However, the results are concordant: Ultrasound measurements of lower uterine segment thickness are strongly correlated with the operative findings observed during cesarean delivery. Moreover, the thinner the lower uterine segment on ultrasound, the higher the likelihood of a uterine defect. Two randomized trials have recently been published. The PRISMA cluster randomized controlled trial evaluated a multifaceted intervention including an ultrasound estimation of the risk of uterine rupture by ultrasound measurement of the lower uterine segment thickness and aimed at helping women in their choice of mode of delivery after a previous cesarean delivery. This multifaceted intervention resulted in a significant reduction in the rates of major perinatal and maternal morbidity, without any increase in the rate of cesarean delivery or uterine rupture. However, due to its design, it is impossible to specifically specify the benefit of lower uterine segment measurement in reducing major maternal and perinatal morbidity since the trial combined several interventions. The LUSTrial randomized controlled trial evaluated the impact on maternal-fetal morbidity and mortality of proposing a mode of delivery based on ultrasound measurement of the lower uterine segment thickness compared to usual care among women with a history of cesarean delivery. Ultrasound measurement of lower uterine segment thickness was not associated with a statistically significant reduction in maternal-fetal morbidity and mortality compared to usual care. In this literature review, we will mainly detail and analyze the results of this trial.

Routine screening for placenta accreta spectrum

Screening for clinically significant placenta accreta spectrum (PAS) is possible with a high degree of accuracy (both sensitivity and specificity >90-95%). The group of women to focus on are those with placenta previa and one or more prior Cesarean deliveries. Screening for PAS not associated with placenta previa is not as productive, and several false negatives have been described. The results of the screening program indicate that women have a low or high probability of PAS. Screen-positive women or those with uncertain ultrasound features should be referred to a center of excellence. Those confirmed to have a high probability of PAS should electively be delivered at such centers.

Intrapartum ultrasound measurement of the lower uterine segment thickness in parturients with previous scar in labor: a cross-sectional study

Background

There is a lack of reliable methods to estimate the risk of uterine rupture or dehiscence during a trial of labor in women with previous cesarean sections. This study aimed to assess the lower uterine segment and myometrial thickness by ultrasonography in women with previous cesarean sections during labor and assess their association with the uterine defect.

Methods

A cross-sectional study was conducted on 161 women in the active phase of labor having one previous cesarean section. The study was conducted et al.-Azhar University Hospital, Assiut City, Egypt, from March 2018 to March 2019. Ultrasound measurements of lower uterine segment thickness and myometrial thickness were conducted by vaginal and abdominal ultrasound by two observers. The correlation of both thicknesses with the uterine defect was analyzed.

Results

Uterine defects were reported in 42 women (25.9%), uterine rupture in four women (2.5%), and dehiscence in 38 women (23.5%). The uterine defects were not associated with maternal factors (maternal age, gestational age at labor, body mass index, birth weight, interpregnancy, and inter-delivery interval). Receiver operating curve analysis demonstrated that lower uterine segment thickness was linked with uterine defect, with an area under the curve of 60% (95% CI, 51–70%, P = 0.044). Myometrial thickness was also linked to the uterine defect, with an area under the curve of 61% (95% CI, 52–71%, P = 0.025). Full lower uterine segment thickness of 2.3 mm and myometrial thickness of 1.9 mm were the cutoff value with the best combination of sensitivity and specificity for the uterine defect. Lower uterine segment thickness (OR = 0.49, 95%CI 0.24–0.96) and myometrial thickness (OR = 0.44, 95%CI 0.20–0.94) were significantly associated with the uterine defect. Lower uterine segment thickness (OR = 0.41, 95%CI 0.22–0.76) and myometrial thickness (OR = 0.33, 95%CI 0.16–0.66) were also significantly associated with cesarean section delivery.

Conclusion

A lower uterine segment thickness of 2.3 mm and myometrial thickness of 1.9 mm during the first stage of labor are associated with a high risk of uterine defects during a labor trial. These measurements during labor can have a practical application in deciding the mode of delivery in women with previous cesarean sections and might reduce uterine rupture.

Transabdominal versus transvaginal ultrasound to assess the thickness of lower uterine segment at term in women with previous cesarean section

OBJECTIVE

This study aims to compare transvaginal (TVS) and transabdominal (TAS) ultrasonography precision in to evaluate the lower uterine (LUS) thickness in women with a previous Cesarean section at the term pregnancy; to be an effective method for assessment of previous cesarean scar strength.

MATERIAL AND METHODS

An observational cross-sectional study was conducted at kasr el-ainy Hospital in Egypt. From May to November 2020, we admitted 130 pregnant women at term with a previous cesarean section for an elective cesarean delivery. Lower uterine segment thickness was obtained using both transvaginal ultrasound and transabdominal ultrasound before the cesarean. The exact thickness of the lower uterine segment was recorded using a sterile metal ruler before the neonate had been delivered.

RESULTS

The mean thickness of the lower uterine segment obtained by transabdominal ultrasound was 5.2 ± 1.6 mm and 4.8 ± 1.33 mm by transvaginal ultrasound, then compared each of them to the mean actual thickness, which was 4.5 ± 1.22 mm. The lower uterine segment thickness with transabdominal ultrasound showed a good correlation (r = 0.722) with the actual thickness, the correlation with transvaginal ultrasound was better (r = 0.944). A cut-off value transvaginal ultrasound of 3.65 mm with 90.8% sensitivity and 65.6% specificity.

CONCLUSION

Transvaginal ultrasound is more accurate in assessing the thickness of the lower uterine segment than transabdominal ultrasound. A total lower uterine segment thickness of <3.65 is considered a thin scar, and <2.85 mm is associated with a higher risk of uterine dehiscence. The trial was registered in ClinicalTrials.gov registry with clinical trial. https://clinicaltrials.gov/ct2/show/NCT04687891.

Evaluation of the usefulness of ultrasound measurement of the lower uterine segment before delivery of women with a prior cesarean delivery: a randomized trial

BACKGROUND

The main reason to avoid trial of labor after cesarean delivery is the possibility of uterine rupture. Identifying women at risk is thus an important aim, for it would enable women at low risk to proceed with a secure planned vaginal birth.

OBJECTIVE

To evaluate the impact of proposing mode of delivery based on the ultrasound measurement of the lower uterine segment thickness on a composite outcome of maternal-fetal mortality and morbidity, compared with usual management, among pregnant women with a previous cesarean delivery.

STUDY DESIGN

This multicenter, randomized, controlled, parallel-group, unmasked trial was conducted at 8 referral university hospitals with a neonatal intensive care unit and enrolled 2948 women at 36 weeks 0 days to 38 weeks 6 days of gestation with 1 previous low transverse cesarean delivery and no contraindication to trial of labor. Women in the study group had their lower uterine segment thickness measured by ultrasound. Those with measurements >3.5 mm, were encouraged to choose a planned vaginal delivery, and those with measurements ≤3.5 mm, were encouraged to choose a planned repeat cesarean delivery. This measurement was not taken in the control group; their mode of delivery was decided according to standard management. The primary outcome was a composite criterion comprising maternal mortality, uterine rupture, uterine dehiscence, hysterectomy, thromboembolic disease, transfusion, endometritis, perinatal death, or neonatal encephalopathy. Prespecified secondary outcomes were repeat cesarean deliveries, elective or after trial of labor.

RESULTS

The study group included 1472 women, and the control group included 1476 women. These groups were similar at baseline. The primary outcome occurred in 3.4% of the study group and 4.3% of the control group (relative risk, 0.78; 95% confidence interval, 0.54-1.13: risk difference, -1.0%; 95% confidence interval, -2.4 to 0.5). The uterine rupture rate in the study group was 0.4% and in the control group 0.9% (relative risk, 0.43; 95% confidence interval, 0.15-1.19). The planned cesarean delivery rate was 16.4% in the study group and 13.7% in the control group (relative risk, 1.21; 95% confidence interval, 1.00-1.47), whereas the rates of cesarean delivery during labor were 25.1% and 25.0% (relative risk, 1.01; 95% confidence interval, 0.89-1.14) in the study and control groups, respectively.

CONCLUSION

Ultrasound measurements of lower uterine segment thickness did not result in a statistically significant lower frequency of maternal and perinatal adverse outcomes than standard management. However, because this study was underpowered, further research should be encouraged.

Assessment of the necessity of uterine artery embolization during suction and curettage for caesarean scar pregnancy: a prospective cohort study

Background

Uterine artery embolization (UAE) followed by suction and curettage is a common conservative treatment for caesarean scar pregnancy (CSP), but the advantages of suction and curettage alone are underestimated due to the lack of standards for selecting appropriate cases for which this approach would be applicable. We sought to identify indicators with which to assess the need for UAE during suction and curettage.

Methods

The prospective cohort consisted of 105 women diagnosed with CSP in Peking Union Medical College Hospital between January 2016 and September 2018 who were followed up until 60 days after surgery. The main outcome was the therapy used, and secondary outcomes included recovery, bleeding, surgery time, length of hospital stay, and total cost.

Results

We found that β-human chorionic gonadotropin (β-hCG) levels were significantly lower (P < 0.05), foetal cardiac activity was significantly lower (P < 0.05), the myometrial layer was significantly thicker (P < 0.05), expenditures were lower and lengths of hospital stay were shorter in patients who received suction and curettage alone (the non-UAE group) than in those who received UAE followed by suction and curettage (the UAE+ group). In addition, for CSP patients, UAE might be less necessary when the myometrial thickness is ≥2 mm and the gestational sacmeasures ≤5 cm, and suction and curettage alone may be safer for these patients.

Conclusion

Suction and curettage alone is a more suitable option than UAE followed by suction and curettage because the former carries a lower cost, shorter length of hospital stay, and lower risk of adverse events. Regarding risk factors, patients with a lower uterine segment thickness ≥ 2 mm and a gestational mass diameter ≤ 5 cm have an increased probability of being successfully treated with suction and curettage alone.

Comparison of the lower uterine segment in pregnant women with and without previous cesarean section in 3 T MRI

BACKGROUND

Prenatal risk stratification of women with previous cesarean section (CS) by ultrasound thickness measurement of the lower uterine segment (LUS) is challenging. There is a wide range of proposed cutoff values and a valuable algorithm for selection before birth is not available. Using 3 T magnetic resonance imaging (MRI), we aimed to identify possible shortcomings of the current protocols used for birth selection after CS. Therefore, we evaluated anatomic and morphologic differences of the LUS and its thickness in patients with CS and those without. Possible impact factors on LUS thickness were studied.

METHODS

We retrospectively analyzed 3 T MRI scans of 164 pregnant women in their second or third trimester, with (patient group, n = 60) and without previous CS (control group, n = 104). Sagittal T2-weighted images were studied. Normal findings of the LUS in MRI, reliability of MRI measurements, as well as factors influencing LUS thickness were assessed. MRI findings were compared to intraoperative findings.

RESULTS

MRI provided good intra- (ICC 0.872) and fair inter-rater reliability (ICC 0.643). The relationship of the LUS and the cesarean scar to the surrounding anatomical structures and also its morphology varied strongly in patients and controls. Scar identification was possible in only 9/60 (15.0%) patients. The LUS was thinner in patients (1.9 ± 0.7 mm) than in controls (2.7 ± 1.3 mm). An LUS thinning up to 1 mm was observed in 23% of women without a previous CS and in 34% of women with normal intraoperative findings. Suspicion of a uterine dehiscence (LUS thickness < 1 mm) was only found in the patient group (5/59 (8.5%)) and was intraoperatively confirmed. In controls, LUS thickness was influenced by fetal weight, gestational age and amniotic fluid amounts.

CONCLUSION

Variability in anatomy, thickness and morphology seem to limit common prenatal LUS imaging diagnostics. Therefore, we consider that diagnostic protocols must be re-evaluated and imaging should be adjusted to the individual patient conditions. Due to its independency of ultrasound limitations, an additional MRI might be useful for altered anatomy and impaired ultrasound conditions. An LUS thinning up to 1 mm might be a normal finding and should be further investigated as reference value.

Lower uterine segment thickness in assessing whether cesarean scar pregnancy patients could be treated with suction curettage

Background: To find a suitable indicator in selecting appropriate patients with cesarean scar pregnancy (CSP) for treatment with ultrasound-guided suction curettage alone.Methods: A retrospective review of all women with CSP treated at the Tongji Hospital, Wuhan, China, between 1 January 2013 and 31 December 2015 was conducted. The women were grouped according to the following management options: ultrasound-guided suction curettage only (Group 1); combination with other therapeutic options (Group 2). The clinical characteristics and outcomes were analyzed.Results: Of 174 patients with lower uterine segment myometrium thickness ≥0.2 cm, 93 (53.4%) patients underwent ultrasound-guided suction curettage only, 81 (46.6%) patients underwent a combination with other therapeutics. Clinical characteristics of women who underwent ultrasound-guided suction curettage alone did not significantly differ from those who were treated with combination. Intraoperative blood loss and length of stay differed significantly between the two groups.Conclusions: In appropriate CSP cases with lower uterine segment myometrium thickness more than 0.2 cm, ultrasound-guided suction curettage appears to be a reliable treatment option producing satisfying success rates, lower blood loss, and a shorter hospital-stay compared to combined therapies.

[Lower Uterine Segment Trial: A pragmatic open multicenter randomized trial]

BACKGROUND

The data from literature show that trial of labor and elective repeat cesarean delivery after a prior cesarean delivery both present significant risks and benefits, and these risks and benefits differ for the woman and her fetus. The benefits to the woman can be at the expense of her fetus and vice-versa. This uncertainty is compounded by the scarcity of high-level evidence that preclude accurate quantification of the risks and benefits that could help provide a fair counseling about a trial of labor and elective repeat cesarean delivery. An interesting way of research is to evaluate the potential benefits of a decision rule associated to the ultrasound measurement of the lower uterine segment (LUS). Indeed, ultrasonography may be helpful in determining a specific risk for a given patient by measuring the thickness of the LUS, i,e, the thickness of the cesarean delivery scar area. Although only small and often methodologically biased data have been published, they look promising as their results are concordant: ultrasonographic measurements of the LUS thickness is highly correlated with the intraoperative findings at cesarean delivery. Furthermore, the thinner the LUS becomes on ultrasound, the higher the likelihood of a defect in the LUS. Finally, ultrasound assessment of LUS has an excellent negative predictive value for the risk of uterine defect. Therefore, this exam associated with a rule of decision could help to reduce the rate of elective repeat cesarean delivery and especially to reduce the fetal and maternal mortality and morbidity related to trial of labor after a prior cesarean delivery.

METHODS/DESIGN

This is a pragmatic open multicenter randomized trial with two parallel arms. Randomization will be centralized and computerized. Since blindness is impossible, an adjudication committee will evaluate the components of the primary composite outcome in order to avoid evaluation bias. An interim analysis will be planned mid-strength of the trial. Ultrasound will be performed by expert sonographers after certification by the main investigator. Women aged 18 years or older are eligible for this trial if they have a singleton pregnancy in cephalic presentation at a gestational age from 36 to 38 weeks, a previous low transverse cesarean delivery and sign the informed consent sheet. Women will be asked to participate in this study when they reach a term of 36 to 38 weeks of gestation. After agreement, women will be randomized into two groups: in the study group, they will have the LUS measured by ultrasound and the patient will be informed that, based on a threshold value of 3.5mm for the ultrasound measurement of the LUS thickness, the patient with a higher measurement will be considered at low risk and will be encouraged to choose a trial of labor whereas the patient with a measurement is equal to or less than this threshold will be considered at risk and encouraged to choose an elective repeat cesarean; in the control group, ultrasound LUS measurement will not be performed. The mode of delivery will be decided according to standard practice at the center. The primary composite outcome will include: uterine rupture, uterine dehiscence, hysterectomy, thromboembolic complications, transfusion, endometritis, maternal mortality, fetal prenatal and intrapartum mortality, hypoxic-ischemic encephalopathy and neonatal mortality.

DISCUSSION

This trial assesses the efficacy of ultrasound measurement of the lower uterine segment in women with a prior cesarean delivery in reducing fetal and maternal morbidity and mortality and it will provide evidence in order to establish clinical recommendations.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT01916044 (date of registration: 5 August 2013).

Cesarean section scar dehiscence during pregnancy: Case reports

Background:

The incidence of cesarean section increased worldwide with subsequent increase in the risk of cesarean section scar dehiscence (CSSD). The clinical significance and the management of the CSSD are still unclear.

Case Reports:

Here, we report two cases of CSSD. A 35-year-old woman, gravida 2, previous CS, due to preterm premature rupture of membranes (PPROM) and breech presentation at 30 weeks, was admitted for elective CS at 38^+3d weeks’ gestation. During the second elective CS, it was seen that the site of the previous CS scar was very thin along its whole length and the anterior uterine wall was completely deficient, leaving visible bulging fetal membranes and moving baby underneath. A 32-year-old woman, previous three CSs, was admitted as unbooked case without any antenatal records at 29^+4d weeks’ gestation, triplet pregnancy with preterm labor. She received betamethasone and magnesium sulfate (MgSO₄) for fetal lung and fetal brain protection, respectively, followed by emergency CS. During the CS, the previous CSs scars were dehiscent over more than half of its length and the anterior uterine wall was missing leaving visible fetal membranes. The uterine incision of the studied women was repaired in two layers using vicryl 0 interrupted simple stitches for the first layer, followed by interrupted mattress stitches for the second layer. The studied women had uneventful postoperative recovery and were discharged from the hospital after counseling regarding intraoperative findings, uterine incisions repair, and future pregnancies.

Conclusion:

It is useful to assess the lower uterine segment of women with previous CS using the available ultrasound facilities. If the CSSD is diagnosed before the elective CS, the surgeon should prepare himself with the safest uterine incision with least possible complications and the best way of repair of the defective or dehiscent uterine wall.

Single versus double-layer uterine closure at cesarean: impact on lower uterine segment thickness at next pregnancy

BACKGROUND

Uterine rupture is a potential life-threatening complication during a trial of labor after cesarean delivery. Single-layer closure of the uterus at cesarean delivery has been associated with an increased risk of uterine rupture compared with double-layer closure. Lower uterine segment thickness measurement by ultrasound has been used to evaluate the quality of the uterine scar after cesarean delivery and is associated with the risk of uterine rupture.

OBJECTIVE

To estimate the impact of previous uterine closure on lower uterine segment thickness.

STUDY DESIGN

Women with a previous single low-transverse cesarean delivery were recruited at 34-38 weeks' gestation. Transabdominal and transvaginal ultrasound evaluation of the lower uterine segment thickness was performed by a sonographer blinded to clinical data. Previous operative reports were reviewed to obtain the type of previous uterine closure. Third-trimester lower uterine segment thickness at the next pregnancy was compared according to the number of layers sutured and according to the type of thread for uterine closure, using weighted mean differences and multivariate logistic regression analyses.

RESULTS

Of 1613 women recruited, with operative reports available, 495 (31%) had a single-layer and 1118 (69%) had a double-layer closure. The mean third-trimester lower uterine segment thickness was 3.3 ± 1.3 mm and the proportion with lower uterine segment thickness <2.0 mm was 10.5%. Double-layer closure of the uterus was associated with a thicker lower uterine segment than single-layer closure (weighted mean difference: 0.11 mm; 95% confidence interval [CI], 0.02 to 0.21 mm). In multivariate logistic regression analyses, a double-layer closure also was associated with a reduced risk of lower uterine segment thickness <2.0 mm (odd ratio [OR], 0.68; 95% CI, 0.51 to 0.90). Compared with synthetic thread, the use of catgut for uterine closure had no significant impact on third-trimester lower uterine segment thickness (WMD: -0.10 mm; 95% CI, -0.22 to 0.02 mm) or on the risk of lower uterine segment thickness <2.0 mm (OR, 0.95; 95% CI, 0.67 to 1.33). Finally, double-layer closure was associated with a reduced risk of uterine scar defect (RR, 0.32; 95% CI, 0.17 to 0.61) at birth.

CONCLUSION

Compared with single-layer closure, a double-layer closure of the uterus at previous cesarean delivery is associated with a thicker third-trimester lower uterine segment and a reduced risk of lower uterine segment thickness <2.0 mm in the next pregnancy. The type of thread for uterine closure has no significant impact on lower uterine segment thickness.

Age-related changes in thickness of anterior lower uterine segment in normal singleton pregnancy during 20-35 weeks' gestation

PURPOSE

To observe age-related changes in the anterior lower uterine segment (LUS) thickness in normal pregnancy from 20 to 35 weeks' gestation.

METHODS

Subjects were 235 uncomplicated singleton cases that underwent single ultrasound examination at 4-week intervals during 20-35 weeks' gestation. Sagittal LUS sections were evaluated with transvaginal ultrasonography. Anterior LUS thickness (Th) was measured every centimeter from the lowest bladder point (Th0cm) to 4 cm from that point (Th4cm). Th values were standardized by dividing by the Th0cm value. Intragroup comparisons of standardized Th values and intergroup comparisons of actual Th values were made according to gestational age. Statistical analyses were performed with the Kruskal-Wallis and Tukey honest standard deviation tests; significance was set at p < 0.05.

RESULTS

In the 20-23-, 24-27- and 32-35-week groups, standardized Th decreased from Th0cm to Th2cm; in the 28-31-week group standardized Th decreased from Th0cm to Th3cm. Median Th3cm values decreased from 5.0 mm at 20-23 weeks to 3.0 mm at 28-31 weeks, but remained unchanged thereafter.

CONCLUSIONS

The anterior LUS gradually thinned from Th0cm to Th3cm at 20-35 weeks' gestation. Th3cm became increasingly thin between 20-23 and 28-31 weeks' gestation.

Ultrasound Assessment of Lower Uterine Segment Thickness During Pregnancy, Labour, and the Postpartum Period

OBJECTIVES

To evaluate the normal ranges of lower uterine segment (LUS) thickness throughout pregnancy in women without a previous cesarean and to evaluate the relationship between ultrasound and intraoperative LUS thickness.

METHODS

We assessed LUS thickness using transabdominal and transperineal longitudinal scan at each week of gestation, during labour, and in the postpartum period in 1000 pregnant women without previous CS. Secondly, we assessed LUS thickness immediately before CS (using ultrasound) and intraoperatively (using ophthalmic calipers) immediately before delivery of the fetus in 35 women with a previous CS and 29 women without previous CS undergoing elective CS before labour.

RESULTS

We performed 20 307 LUS thickness measurements in between 119 and 944 women at each week of gestation, in 944 women during labour, and in 936 women after delivery. We observed a strong relationship between transabdominal and transperineal ultrasound (P < 0.001) and an inverse correlation between LUS thickness and gestational age (P < 0.001), with a mean thickness of 5.1 ± 1.4 mm at 20 weeks, 3.6 ± 1.3 mm at 30 weeks, and 2.3 ± 0.6 mm at 40 weeks of gestation. In women undergoing elective CS, we observed a strong relationship between antepartum and intraoperative LUS thickness (P < 0.001), with mean thicknesses of 2.2 ± 0.7 mm in 28 women without thinning of LUS; 0.8 ± 0.1 mm in four women with grade II uterine scar dehiscence; and 0.4 ± 0.1 mm in three women with grade III dehiscence. A LUS myometrial thickness less than 1.2 mm could have predicted all grade II and grade III uterine scar dehiscences without false-positive cases.

CONCLUSION

LUS thickness decreases with gestational age and correlates strongly with the intraoperative LUS thickness in women with a previous CS.

Sonographic prediction of scar dehiscence in women with previous cesarean section

PURPOSE

To estimate the risk of uterine dehiscence/rupture in women with previous cesarean section (CS) by comparing the thickness of lower uterine segment (LUS) and myometrium with trans-abdominal (TAS) and trans-vaginal sonography (TVS).

METHOD

In this case-control study, in 100 pregnant women posted for elective CS (with or without previous CS; group 1 and group 2 respectively), the thickness of LUS and myometrium was measured sonographically (TAS and TVS). Intra-operatively, LUS was graded (grades I-IV), and its thickness was measured with calipers. The primary outcome of the study was correlation between echographic measurements (TAS and TVS) and features of LUS (grades I-IV) at the time of CS. Secondary outcomes were correlation between myometrial thickness, number of previous CS, and inter-delivery interval with LUS (grades I-IV).

RESULTS

Sonographic measurements of LUS and myometrium were significantly different between the two groups (both TAS and TVS p value = 0.000 each). However, the number of previous CS (p = 0.440) and inter-delivery interval (p = 0.062) had no statistically significant correlation with thickness of LUS.

CONCLUSIONS

Sonographic evaluation of LUS scar and myometrial thickness (both with TAS and TVS) is a safe, reliable, and non-invasive method for predicting the risk of scar dehiscence/rupture. Specific guidelines for TOLAC, after sonographic assessment of women with previous CS, are need of the hour.

Transvaginal ultrasound assessment of uterine scar after previous caesarean section: comparison with 3T-magnetic resonance diffusion tensor imaging

PURPOSE

This study aimed to evaluate 3-T magnetic resonance imaging in the analysis of caesarean scars in women with prior caesarean section (pCS) and investigate the potential added value of diffusion tensor imaging (3T-MR-DTI) with fibre tracking reconstruction, compared with transvaginal ultrasound (TVUS).

METHODS

Thirty women who had previously undergone elective CS in a singleton pregnancy at term were examined (19 women with one pCS formed group 1 and 11 women with two pCS formed group 2). Patients underwent TVUS and 3T-MR-DTI within 2 days. Twelve women with prior vaginal delivery served as controls and underwent only 3T-MR. Uterine fibre architecture was depicted by MR-DTI with 3D tractography reconstruction providing quali-quantitative analysis of fibre, described as the reduction of number of longitudinal fibres that run through the uterine scar.

RESULTS

Six subjects were excluded. According to 3T-MR morphology, scars were described as linear (n = 12) and retracting (n = 12); disagreement with TVUS was 54 %. The thickness of myometrium at the scar level was found to be significantly greater with 3T-MR compared to TVUS in linear scars (p = 0.01). No difference was found among retracting scars. In controls, according to 3T-MR-DTI, longitudinal myometrial fibres running in the anterior wall were similar to those in the posterior wall at same level -2 %; -27 % + 22 %). In groups 1 and 2 there was significant reduction in anterior fibres compared to posterior ones (-53 %; -77 % - 34 %; p = 0.0001). Among retracting scars, fibre reduction was significantly higher compared to linear scars, p < 0.016.

CONCLUSIONS

The added value of 3T-MR with DTI lies in the prompt evaluation of muscle fibre remaining at scar level.

Comparison of scar thickness measurements using trans-vaginal sonography and MRI in cases of pregnancy with previous caesarean section. Do they correlate with actual scar thickness?

The aim of this study was to evaluate scar thickness in cases of pregnancy with previous caesarean section, by trans-vaginal sonography (TVS) and magnetic resonance imaging (MRI), and to correlate precision of radiologically-measured scar thickness with actual measurement of scar thickness. A total of 35 pregnant patients with previous caesarean section planned for elective caesarean section, were evaluated prospectively. Their scar thickness was measured by TVS and MRI on the day of elective repeat caesarean section. These measurements were correlated with each other and with scar thickness measured during elective repeat caesarean section by using a caliper. The correlation coefficients between scar thickness measured by TVS and MRI with peroperative evaluation with a caliper, were +0.72 and +0.59, respectively. The study concluded that as MRI is a costlier modality and TVS has better correlation coefficient with actual scar thickness, TVS can be considered to be the better modality for antenatal scar thickness measurement.

Sonographic measurement of lower uterine segment thickness to predict uterine rupture during a trial of labor in women with previous Cesarean section: a meta-analysis

OBJECTIVE

To evaluate the accuracy of antenatal sonographic measurement of lower uterine segment (LUS) thickness in the prediction of risk of uterine rupture during a trial of labor (TOL) in women with a previous Cesarean section (CS).

METHODS

PubMed and EMBASE were searched to identify articles published on the subject of sonographic LUS measurement and occurrence of a uterine defect after delivery. Four independent researchers performed identification of papers and data extraction. Selected studies were scored on methodological quality, and sensitivity and specificity of measurement of LUS thickness in the prediction of a uterine defect were calculated. We performed bivariate meta-analysis to estimate summary receiver-operating characteristics (sROC) curves.

RESULTS

We included 21 studies with a total of 2776 analyzed patients. The quality of included studies was good, although comparison was difficult because of heterogeneity. The estimated sROC curves showed that measurement of LUS thickness seems promising in the prediction of occurrence of uterine defects (dehiscence and rupture) in the uterine wall. The pooled sensitivity and specificity of myometrial LUS thickness for cut-offs between 0.6 and 2.0 mm was 0.76 (95% CI, 0.60-0.87) and 0.92 (95% CI, 0.82-0.97); cut-offs between 2.1 and 4.0 mm reached a sensitivity and specificity of 0.94 (95% CI, 0.81-0.98) and 0.64 (95% CI, 0.26-0.90). The pooled sensitivity and specificity of full LUS thickness for cut-offs between 2.0 and 3.0 mm was 0.61 (95% CI, 0.42-0.77) and 0.91 (95% CI, 0.80-0.96); cut-offs between 3.1 and 5.1 mm reached a sensitivity and specificity of 0.96 (95% CI, 0.89-0.98) and 0.63 (95% CI, 0.30-0.87).

CONCLUSIONS

This meta-analysis provides support for the use of antenatal LUS measurements in the prediction of a uterine defect during TOL. Clinical applicability should be assessed in prospective observational studies using a standardized method of measurement.

Measurements of the lower uterine segment during gestation

PURPOSE

To establish normal values for the lower uterine segment (LUS) thickness and to recognize factors that may affect these values.

METHODS

In this cross-sectional study, we measured the LUS thickness in women between 11 and 41 weeks gestation. Women with placental abnormalities and fetal anomalies were excluded. Fetal weight, location of placental implantation, and cervical length were estimated. The LUS was examined to identify the thinnest zone and evaluated using the transvaginal approach with an empty urinary bladder. Full LUS thickness was measured with a caliper at the inner surface of the posterior bladder wall and another caliper at the interface between the amniotic fluid and the decidua. The myometrium was measured with the first caliper at the interface between the amniotic fluid and the deciduas and the second between the bladder wall and the myometrium. Normal values for the LUS were established throughout gestation, and correlations between the LUS gestational age, fetal weight, previous cesarean section, and other parameters were examined.

RESULTS

Overall, 350 women were included in our study. Median parity was 1 (0-6) and the majority (62%, 218/350) of women have not had a previous cesarean section. The LUS thickness inversely correlated with gestational week (Pearson's r = -0.11, p < 0.03). When stratifying the linear regression model to women with and without a history of a previous cesarean section, it was demonstrated that gestational age was moderately correlated with LUS only in the second group of patients (Pearson's r = -0.16, p = 0.1 and Pearson's r = -0.47, p < 0.0001, respectively). During the post term period, patients who had had a previous cesarean section had significantly thinner LUS compared with patients who had not had a previous cesarean section (46 mm ± 20 versus 59 mm ± 20, p = 0.002, respectively). Neither parity nor the number of previous cesarean sections were found to correlate with the thickness of the LUS (p > 0.05). Multivariate linear regression (R(2) = 0.215, F(2, 63) = 9.021, p < 0.001) demonstrated that both gestational week (β = -0.13, p < 0.04) and cesarean section (β = -0.01, p < 0.0001) were independent factors associated with the thickness of the LUS; for every 1 week increase in gestational week, there was a 1.3 mm decrease in the total thickness of the LUS CONCLUSIONS: We have established reference ranges for LUS thickness throughout gestation. The LUS thickness decreases throughout gestation in singleton pregnancies and is significantly thinner in postterm period pregnant women with a previous cesarean section.

Interpregnancy interval and obstetrical complications

Obstetricians are often presented with questions regarding the optimal interpregnancy interval (IPI). Short IPI has been associated with adverse perinatal and maternal outcomes, ranging from preterm birth and low birth weight to neonatal and maternal morbidity and mortality. Long IPI has in turn been associated with increased risk for preeclampsia and labor dystocia. In this review, we discuss the data regarding these associations along with recent studies revealing associations of short IPI with birth defects, schizophrenia, and autism. The optimal IPI may vary for different subgroups. We discuss the consequences of short IPI in women with a prior cesarean section, in particular the increased risk for uterine rupture and the considerations regarding a trial of labor in this subgroup. We review studies examining the interaction between short IPI and advanced maternal age and discuss the risk-benefit assessment for these women. Finally, we turn our attention to women after a stillbirth or an abortion, who often desire to conceive again with minimal delay. We discuss studies speaking in favor of a shorter IPI in this group. The accumulated data allow for the reevaluation of current IPI recommendations and management guidelines for women in general and among subpopulations with special circumstances. In particular, we suggest lowering the current minimal IPI recommendation to only 18 months (vs 24 months according to the latest World Health Organization recommendations), with even shorter recommended minimal IPI for women of advanced age and those who conceive after a spontaneous or induced abortion.

Effective anatomical and functional status of the lower uterine segment at term: estimating the risk of uterine dehiscence by ultrasound

OBJECTIVE

To define the role of lower uterine segment (LUS) evaluation at term.

DESIGN

Observational case-control study.

SETTING

University hospital.

PATIENT(S)

Ninety-four patients were divided into two groups. Group A consisted of 45 multiparous single fetus pregnant women with up to two previous cesarean sections (CS). Group B consisted of 49 multiparous pregnant women with up to three vaginal deliveries and no uterine scars.

INTERVENTION(S)

Total LUS and myometrial thickness were measured by sonogram in all patients before undergoing a CS.

MAIN OUTCOME MEASURE(S)

The primary outcome is a correlation between echographic measurements and features of the LUS at the time of CS. The secondary outcome is a definition of a correlation between the number of previous CS, interdelivery interval time, and features of the LUS (grades I-IV).

RESULT(S)

Sonographic measurements revealed significant differences in LUS size and myometrial thickness between the two groups. Grades III and IV of LUS were only observed in group A. An interdelivery interval <18 months, LUS thickness ≤ 3.0 mm, and myometrial thickness < 1.5 mm were statistically significant predictors of LUS grades III and IV. Number of previous CS showed no correlation with surgical LUS status.

CONCLUSION(S)

Sonographic evaluation of the LUS may be a noninvasive, reproducible, and safe technique for defining the risk of uterine dehiscence, with a sensitivity of 100% and specificity of 85% (positive predictive value, 45%; negative predictive value, 100%).

Prediction of scar integrity and vaginal birth after caesarean delivery

A statistically significant association with uterine rupture during a trial of labour after caesarean delivery was found in at least two studies for the following variables: inter-delivery interval (higher risk with short interval), birth weight (higher risk if 4000 g or over), induction of labour (higher risk), oxytocin dose (higher risk with higher doses), and previous vaginal delivery (lower risk). However, no clinically useful risk estimation model that includes clinical variables has been published. A thin lower uterine segment at 35-40 weeks, as measured by ultrasound in women with a caesarean hysterotomy scar, increases the risk of uterine rupture or dehiscence. No cut-off for lower uterine segment thickness, however, can be suggested because of study heterogeneity, and because prospective validation is lacking. Large caesarean hysterotomy scar defects in non-pregnant women seen at ultrasound examination increase the risk of uterine rupture or dehiscence in subsequent pregnancy, but the strength of the association is unknown. To sum up, we currently lack a method that can provide a reliable estimate of the risk of uterine rupture or dehiscence during a trial of labour in women with caesarean hysterotomy scar(s).

Factors associated with lower uterine segment thickness near term in women with previous caesarean section

OBJECTIVE

To estimate the association between potential influencing factors and lower uterine segment (LUS) thickness at term in women with previous Caesarean section.

METHODS

We conducted a cohort study of women with previous low-transverse Caesarean section undergoing ultrasonographic measurement of LUS thickness between 35 and 38 weeks' gestation in a tertiary care centre between 2006 and 2009. Measurements of the full LUS thickness and the myometrial LUS thickness were performed both transabdominally and transvaginally. The thinnest measurements for both full and myometrial LUS thicknesses were considered dependent variables. Non-parametric analyses, multivariate linear regression analyses, and multivariate regression analyses were used to evaluate the relationships between LUS thickness and the potential influencing factors of maternal age, interdelivery interval, prior vaginal delivery, and several characteristics of the previous Caesarean section.

RESULTS

In 377 women who underwent measurement of LUS thickness, labour before previous Caesarean section was the only characteristic associated with a greater full LUS thickness (an additional 0.9 mm; 95% CI 0.5 to 1.2 mm) in multivariate linear regression analysis. Labour before previous Caesarean section (0.5 mm; 95% CI 0.2 to 0.7 mm) and the use of synthetic sutures (as opposed to catgut sutures) for the closure of the previous hysterotomy incision (0.3 mm; 95% CI 0.02 to 0.5 mm) were the only two variables significantly associated with a thicker myometrial LUS. In multivariate regression analysis, three factors were predictive of a full LUS thickness of > 2.3 mm: the presence of labour, a recurrent indication for Caesarean section, and the use of synthetic sutures for hysterotomy closure at previous Caesarean section (P < 0.05).

CONCLUSION

Labour at the time of previous Caesarean section is associated with a thicker LUS near term in the subsequent pregnancy. The use of synthetic sutures for hysterotomy closure is another factor potentially associated with a thicker LUS.

Reliability of 3-dimensional transvaginal sonographic measurement of lower uterine segment thickness

OBJECTIVES

The purpose of this study was to report the intraobserver and interobserver reliability of transvaginal 3-dimensional (3D) sonographic measurement of lower uterine segment thickness.

METHODS

A prospective study of 60 pregnant women with previous low transverse cesarean deliveries was performed between 35 and 39 weeks' gestation. Two observers, blinded to the clinical data, independently measured the full lower uterine segment thickness by 2-dimensional (2D) transvaginal sonography. Three-dimensional volume data sets of the lower uterine segment were captured and analyzed more than 2 months later by both observers independently. Intraobserver, interobserver, and intermethod reliability was evaluated by median absolute differences, nonparametric limits of agreement, intraclass correlation coefficients (ICCs), and κ coefficients.

RESULTS

The median full lower uterine segment thickness was 3.6 mm (range, 0.9-8.0 mm). Intraobserver reliability (median difference, 0.3 mm [interquartile range (IQR), 0.1-0.6 mm]; ICC, 0.88 [95% confidence interval (CI), 0.81-0.93]; κ, 0.87 [95% CI, 0.69-1.00]) and interobserver reliability (median difference, 0.3 mm [IQR, 0.1-0.5 mm]; ICC, 0.88 [95% CI, 0.81-0.93]; κ, 0.86 [95% CI, 0.66-1.00]) were excellent. Reliability between 3D and 2D sonography was moderate (median difference, 0.6 mm [IQR, 0.2-0.9 mm]; ICC, 0.78 [95% CI, 0.66-0.86]; κ, 0.56 [95% CI, 0.28-0.85]). However, intermethod reproducibility was improved when the full lower uterine segment thickness was less than 3.0 mm (median difference, 0.4 mm [IQR, 0.2-0.9 mm]).

CONCLUSIONS

Full lower uterine segment thickness measured with 3D transvaginal sonographic data sets has excellent intraobserver and interobserver reliability. It also has good reproducibility with 2D sonography when the full lower uterine segment thickness is less than 3.0 mm.

Ultrasound of the gravid uterus

The ultrasound findings involving the gravid uterus will be described with a focus on differentiating normal from pathologic conditions. Topics pertaining to the gravid uterus include uterine fibroids, müllerian anomalies, cervical shortening, the normal and pathologic appearance of cesarean delivery scars, and uterine rupture. Clinical management and therapeutic implications based on sonographic findings will be emphasized.

Impact of labor at prior cesarean on lower uterine segment thickness in subsequent pregnancy

OBJECTIVE

The objective of the study was to identify the factors associated with sonographic lower uterine segment (LUS) thickness near term in women with prior low transverse cesarean.

STUDY DESIGN

A prospective cohort study of women with a single prior low transverse cesarean was conducted. LUS thickness was quantified by transabdominal ultrasound with repeated transvaginal measurement when necessary. The thinnest measurement was considered as the dependent variable. Potential related factors were evaluated with nonparametric analyses and multivariate logistic regressions.

RESULTS

Two hundred thirty-five women were recruited at a mean gestational age of 36.7 +/- 1.3 weeks. The full LUS was thicker in women who had their previous cesarean during the latent phase (2.8 mm; interquartile [IQ], 2.0-3.3 mm) or the active phase of labor (3.1 mm; IQ 2.5-3.9 mm) than in women with previous cesarean prior to labor (2.4 mm; IQ 2.0-3.2 mm). The association remained significant after adjustment for potential confounders.

CONCLUSION

Presence of labor at previous cesarean is associated with a thicker LUS in a subsequent pregnancy.

Prediction of complete uterine rupture by sonographic evaluation of the lower uterine segment

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.

Comparison of transabdominal versus transvaginal ultrasound to measure thickness of the lower uterine segment at term

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.

Uterine dehiscence in term pregnant patients with one previous cesarean delivery: growth factor immunoexpression and collagen content in the scarred lower uterine segment

OBJECTIVE

This study aimed at investigating the relationship between the occurrence of uterine dehiscence in term pregnant scarred uteri and the presence of altered biochemical behavior of the scarring process.

STUDY DESIGN

Collagen content and the expression of transforming growth factor-beta and its isoforms transforming growth factor-beta1 and transforming growth factor-beta3, connective tissue growth factor, basic fibroblast growth factor, vascular endothelial growth factor, platelet-derived growth factor, and tumor necrosis factor-alpha in myometrium of lower uterine segment were assessed in 19 otherwise healthy term patients with one previous cesarean delivery who were not in labor. We were searching for differences between patients who showed uterine dehiscence (9 cases) and patients who showed a normal-appearing scarred lower uterine segment (10 cases). We also evaluated all these features in lower uterine segment from unscarred uteri of 10 otherwise healthy patients who were not in labor.

RESULTS

In the case of uterine dehiscence, the scarred lower uterine segment showed a higher collagen content, a reduction of pan transforming growth factor-beta expression because of a marked decrease or absence of transforming growth factor-beta3, a reduction of connective tissue growth factor, an increase in basic fibroblast growth factor and a slight enhancement in vascular endothelial growth factor, platelet-derived growth factor, and tumor necrosis factor-alpha expression.

CONCLUSION

These findings contribute to meliorate our knowledge about uterine scar healing and allow us to hypothesize that uterine dehiscence of a scarred uterus may be related to altered biochemical behavior of the scarring process.

Sonographic Measurement of the Lower Uterine Segment Thickness in Women With Previous Caesarean Section

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.