Reproducibility of assessment of full-dilatation Cesarean section scar in women undergoing second-trimester screening for preterm birth

Escalating caesarean deliveries and the impact on subsequent preterm birth

The rate of caesarean section, including those performed in-labour, is on the rise. Worldwide 1 in 5 women are delivering by caesarean section. Emerging evidence has demonstrated an association between in-labour caesarean section and mid-trimester loss (delivery between 14 and 24 weeks gestation) as well as spontaneous preterm birth, (delivery before 37 weeks' gestation). This problem is more likely to recur in subsequent pregnancies and is difficult to treat with evidence suggesting that transvaginal cerclage may be a less efficacious preventative measure in women with a short cervix and previous in-labour caesarean section. This review explores the scope of the issue including the evidence for in-labour caesarean section as a risk factor for preterm birth and the possible underlying mechanism. It will discuss management strategies, as well as highlighting areas where further research is required.

Automated cervix biometry, volumetry and normative models for 3D motion-corrected T2-weighted 0.55-3T fetal MRI during 2nd and 3rd trimesters

Fetal MRI provides superior tissue contrast and true 3D spatial information however there is only a limited number of number of MRI studies investigating cervix during pregnancy. Furthermore, there are no clearly formalised protocols or automated methods for MRI cervical measurements. This work introduces the first deep learning pipeline for automated multi-layer segmentation and biometry for 3D T2w images of the pregnant cervix. Evaluation on 20 datasets from 0.55T and 3T acquisitions showed good performance in comparison to manual measurements. This solution could potentially minimise the need for manual editing, significantly reduce analysis time and address inter- and intra-observer bias. Next, we used the pipeline to process 270 normal term cases from 16 to 40 weeks gestational age (GA) range. The inlet diameter and length showed the strongest correlation with GA which is in agreement with the gradual remodeling and softening of the cervix prior to birth. We also generated 3D population-averaged atlases of the cervix that are publicly available online.

Transvaginal cervical cerclage: double monofilament modified Wurm vs single braided McDonald technique

OBJECTIVE

To compare pregnancy outcome in women at high risk of preterm birth undergoing the modified Wurm (two monofilament sutures) vs those undergoing the McDonald (single braided suture) transvaginal cervical cerclage technique.

METHODS

This was a single-center prospective observational study of all women with a singleton pregnancy attending a prematurity surveillance clinic because of an increased risk of preterm birth, and undergoing history- or ultrasound-indicated transvaginal cervical cerclage. Two cerclage techniques were evaluated and the choice of cerclage was at the physician's discretion. In the modified Wurm technique using monofilament material, two circumferential sutures are placed with two insertions each (four in total). Outcomes were compared vs those of women undergoing the McDonald technique (single braided suture using a diamond-type insertion method with four insertions in total). Primary outcome was the rate of preterm birth at < 32 weeks' gestation, with planned subanalyses according to cervical cerclage indication (history- or ultrasound-indicated), preterm birth rate at any gestational age (< 37, < 34, < 28 and < 24 weeks), and sonographic cervical length (CL) of ≤ 25 mm and ≤ 15 mm. Secondary outcome measures included maternal and neonatal adverse events and outcomes, including the pre- and postsurgical characteristics. In addition, a reproducibility analysis using Bland-Altman plots was performed to evaluate the intra- and interobserver reproducibility in assessment of CL on ultrasound examination before and after cerclage.

RESULTS

In total, 147 patients were included in the final analysis: 55 (37%) received modified Wurm cerclage and 92 (63%) received McDonald cerclage. Other than race, demographic characteristics were comparable between the two groups. Of these, 22 (40%) women in the modified Wurm group had history-indicated cerclage, vs 50 (54%) women in the McDonald group; the remaining cerclages were ultrasound-indicated. In women with a short CL (≤ 25 mm), there was a significantly lower rate of preterm birth at < 32 weeks' gestation after modified Wurm compared with the McDonald technique (3 (9%) vs 14 (29%); adjusted odds ratio (aOR), 0.25 (95% CI, 0.06-0.95); P = 0.042). However, the study was underpowered to provide definitive conclusions. In the overall population, there was no significant difference in preterm birth rate for < 32 weeks' gestation between the two techniques (7 (13%) vs 22 (24%); aOR, 0.51 (95% CI, 0.20-1.33); P = 0.169). There was no difference in overall surgical complications between the two techniques. The pregnancy loss rate and composite neonatal morbidity/mortality rate were comparable between the two groups (2 (4%) vs 7 (8%); odds ratio (OR), 0.47 (95% CI, 0.09-2.33); P = 0.485; and 5 (9%) vs 11 (13%); OR, 0.68; (95% CI, 0.22-2.09); P = 0.593, respectively).

CONCLUSIONS

In high-risk women with a sonographic short CL, placement of a modified Wurm cervical cerclage is associated with a lower rate of preterm birth < 32 weeks compared with McDonald cervical cerclage. Further research in larger cohorts is needed to confirm this finding and to determine if this technique reduces the preterm birth rate after elective cervical cerclage without CL shortening. © 2025 The Author(s). Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

Three-Dimensional Volume Ultrasound Assessment of Cesarean Scar Niche and Cervix in Pregnant Women: A Reproducibility Study

OBJECTIVE

To assess the reproducibility of standardized 3-dimensional (3D) ultrasound volume analysis of the dimensions and the position of cesarean birth (CB) scar niche relative to the cervix in pregnant women.

METHODS

This prospective single-center study in women with 1 previous CB ≥8 cm cervical dilatation acquired ultrasound volumes between 11 and 24 weeks' gestation in a mid-sagittal plane. Two experienced operators processed the volumes using virtual organ computer-aided analysis. A CB scar niche was defined as an indentation at the scar site of ≥2 mm in depth. Niche and cervix volumes were calculated using manual contouring. Agreement for categorical variables was expressed using intraclass correlation coefficient (ICC). The Bland-Altman method was used to assess numerical variable reproducibility.

RESULTS

To achieve the desired statistical power, 52 participants were included. The intraobserver agreement on niche classification relative to the internal os was 100%, with an interobserver kappa coefficient of 0.98 (95% confidence interval [CI] 0.97-0.99, P < .05). The intraobserver ICC for niche volume was 0.94 (95% CI 0.90-0.96; P < .001), with a mean difference of -15.32 mm3 (±109.32). The interobserver ICC was 0.78 (95% CI 0.62-0.87; P < .001), with a mean difference of -21.57 mm3 (±202.01). The ICC for niche/cervix volume ratio were 0.94 (95% CI 0.90-0.96; P < .001) and 0.79 (95% CI 0.63-0.87; P < .001) for intra- and interobserver reproducibility, respectively.

CONCLUSIONS

This study demonstrates that 3D CB scar sonographic features are highly reproducible in pregnant women with a history of advanced labor CB. The validated protocol can guide future research on the association with subsequent adverse pregnancy outcomes.

A national survey of clinicians' opinions of rotational vaginal births

INTRODUCTION

Malposition of the fetal head, defined as occiput transverse or posterior positions, occurs in approximately 5% of births. At full cervical dilatation, fetal malposition is associated with an increased risk of rotational vaginal birth. There are three different rotational methods: manual rotation, rotational ventouse or rotational (Kielland's) forceps. In the absence of robust evidence, it is not currently known which of the three methods is most efficacious, and safest for parents and babies.

OBJECTIVE

To gain greater insights into opinions and preferences of rotational birth to explore the acceptability and feasibility of performing a randomised trial comparing different rotational methods.

MATERIAL AND METHODS

A survey was sent via email to obstetricians from the British Maternal Fetal Medicine Society, as well as expert obstetricians and active academics in ongoing research in the UK. The questions focussed on perceived competence, preferred rotational method, location (theatre or labour room), willingness to recruit to an RCT, and its outcome measures. Closed questions were followed by the option of free text to allow further comments. The free text answers underwent thematic analysis.

RESULTS

252 consultant obstetricians responded. The majority stated they were competent in performing manual rotation (88.1%). Half felt proficient using Kielland's rotational forceps (54.4%). Most obstetricians felt skilled in rotational ventouse (76.2%). Manual rotation was the preferred first rotational method of choice in cases of both occiput transverse and posterior positions. The decision for which rotational method to attempt first was considered case-dependent by many. Two thirds of obstetricians would usually conduct rotational births in theatre (67.9%). Over half (52%) do not routinely use intrapartum ultrasound. Most (62.7%) would be willing to recruit to a randomised controlled trial comparing manual versus instrumental rotation. Over half (57.2%) would be willing to recruit to the same RCT if they were the most senior doctor competent in rotational vaginal birth supervising a junior.

CONCLUSION

There is a wide range of practice in conducting rotational vaginal births in the UK. An RCT to investigate the impact of different rotational methods on outcome would be both feasible and desirable, especially in research-active hospitals.

Prediction of spontaneous preterm birth in women with previous full dilatation cesarean delivery

BACKGROUND

A previous term (≥37 weeks' gestation), full-dilatation cesarean delivery is associated with an increased risk for a subsequent spontaneous preterm birth. The mechanism is unknown. We hypothesized that the cesarean delivery scar characteristics and scar position relative to the internal cervical os may compromise cervical function, thereby leading to shortening of the cervical length and spontaneous preterm birth.

OBJECTIVE

This study aimed to determine the relationship of cesarean delivery scar characteristics and position, assessed by transvaginal ultrasound, in pregnant women with previous full-dilatation cesarean delivery with the risk of shortening cervical length and spontaneous preterm birth.

STUDY DESIGN

This was a single-center, prospective cohort study of singleton pregnant women (14 to 24 weeks' gestation) with a previous term full-dilatation cesarean delivery who attended a high-risk preterm birth surveillance clinic (2017-2021). Women underwent transvaginal ultrasound assessment of cervical length, cesarean delivery scar distance relative to the internal cervical os, and scar niche parameters using a reproducible transvaginal ultrasound technique. Spontaneous preterm birth prophylactic interventions (vaginal cervical cerclage or vaginal progesterone) were offered for short cervical length (≤25 mm) and to women with a history of spontaneous preterm birth or late miscarriage after full-dilatation cesarean delivery. The primary outcome was spontaneous preterm birth; secondary outcomes included short cervical length and a need for prophylactic interventions. A multivariable logistic regression analysis was used to develop multiparameter models that combined cesarean delivery scar parameters, cervical length, history of full-dilatation cesarean delivery, and maternal characteristics. The predictive performance of models was examined using the area under the receiver operating characteristics curve and the detection rate at various fixed false positive rates. The optimal cutoff for cesarean delivery scar distance to best predict a short cervical length and spontaneous preterm birth was analyzed.

RESULTS

Cesarean delivery scars were visualized in 90.5% (220/243) of the included women. The spontaneous preterm birth rate was 4.1% (10/243), and 12.8% (31/243) of women developed a short cervical length. A history- (n=4) or ultrasound-indicated (n=19) cervical cerclage was performed in 23 of 243 (9.5%) women; among those, 2 (8.7%) spontaneously delivered prematurely. A multiparameter model based on absolute scar distance from the internal os best predicted spontaneous preterm birth (area under the receiver operating characteristics curve, 0.73; 95% confidence interval, 0.57-0.89; detection rate of 60% for a fixed 25% false positive rate). Models based on the relative anatomic position of the cesarean delivery scar to the internal os and the cesarean delivery scar position with niche parameters (length, depth, and width) best predicted the development of a short cervical length (area under the receiver operating characteristics curve, 0.79 [95% confidence interval, 0.71-0.87]; and 0.81 [95% confidence interval, 0.73-0.89], respectively; detection rate of 73% at a fixed 25% false positive rate). Spontaneous preterm birth was significantly more likely when the cesarean delivery scar was <5.0 mm above or below the internal os (adjusted odds ratio, 6.87; 95% confidence interval, 1.34-58; P =.035).

CONCLUSION

In pregnancies following a full-dilatation cesarean delivery, cesarean delivery scar characteristics and distance from the internal os identified women who were at risk for spontaneous preterm birth and developing short cervical length. Overall, the spontaneous preterm birth rate was low, but it was significantly increased among women with a scar located <5.0 mm above or below the internal cervical os. Shortening of cervical length was strongly associated with a low scar position. Our novel findings indicate that a low cesarean delivery scar can compromise the functional integrity of the internal cervical os, leading to cervical shortening and/or spontaneous preterm birth. Assessment of the cesarean delivery scar characteristics and position seem to have use in preterm birth clinical surveillance among women with a previous, full-dilatation cesarean delivery and could better identify women who would benefit from prophylactic interventions.

Longitudinal change in cervical length following vaginal or abdominal cervical cerclage: a randomized comparison

BACKGROUND

Cervical cerclage has been shown to reduce the risk of recurrent spontaneous preterm birth in a high-risk patient population; however, the mechanism is not well understood. Transabdominal cerclage is superior to low and high vaginal cerclage in reducing early spontaneous preterm birth and fetal loss in women with previous failed vaginal cerclage. Cervical length measurements are commonly used to monitor high-risk women and may explain the mechanism of success.

OBJECTIVE

This study aimed to evaluate the rate of change in longitudinal cervical length after randomized placement of low transvaginal, high transvaginal, or transabdominal cerclage in women with a previous failed vaginal cerclage.

STUDY DESIGN

This was a planned analysis of longitudinal transvaginal ultrasound cervical length measurements from patients enrolled in the Vaginal Randomised Intervention of Cerclage trial, a randomized controlled trial comparing transabdominal cerclage or high transvaginal cerclage with low transvaginal cerclage. Cervical length measurements at specific gestational ages were compared over time and between groups, using generalized estimating equations fitted using the maximum-likelihood random-effects estimator. In addition, cervical length measurements were compared in women with transabdominal cerclage placed before and during pregnancy. The diagnostic accuracy of cervical length as a predictor of spontaneous preterm birth at <32 weeks of gestation was explored.

RESULTS

This study included 78 women who underwent longitudinal cervical length assessment (70% of the analyzed cohort) with a history of failed cerclage, of whom 25 (32%) were randomized to low transvaginal cerclage, 26 (33%) to high transvaginal cerclage, and 27 (35%) to transabdominal cerclage. Abdominal cerclage was superior to low (P=.008) and high (P=.001) vaginal cerclage at maintaining cervical length over the surveillance period (14 to 26 weeks of gestation) (+0.08 mm/week, 95% confidence interval, -0.40 to 0.22; P=.580). On average, the cervical length was 1.8 mm longer by the end of the 12-week surveillance period in women with transabdominal cerclage (+1.8 mm; 95% confidence interval, -7.89 to 4.30; P=.564). High vaginal cerclage was no better than low cervical cerclage in the prevention of cervical shortening; the cervix shortened by 13.2 mm over 12 weeks in those with low vaginal cerclage (95% confidence interval, -21.7 to -4.7; P=.002) and by 20 mm over 12 weeks in those with high vaginal cerclage (95% confidence interval, -33.1 to -7.4; P=.002). Preconception transabdominal cerclage resulted in a longer cervix than those performed during pregnancy; this difference was significant after 22 weeks of gestation (48.5 mm vs 39.6 mm; P=.039). Overall, cervical length was an excellent predictor of spontaneous preterm birth at <32 weeks of gestation (receiver operating characteristic curve, 0.92; 95% confidence interval, 0.82-1.00).

CONCLUSION

In women with a previous failed cervical cerclage, in the next pregnancy, the cervical length in women treated with vaginal cerclage funneled and shortened over time, whereas there was preservation of cervical length in women who receive transabdominal cerclage. Cervical length remained longer in transabdominal procedures performed before pregnancy than in transabdominal procedures performed during pregnancy. Overall, cervical length was an excellent predictor of spontaneous preterm birth in our cohort. Our findings may explain the mechanism of benefit for transabdominal cerclage, with its high placement better maintaining the structural integrity of the cervix at the level of the internal os.