Performance of the First-Trimester Cervical Consistency Index to Predict Preterm Birth

Background/Objectives: Preterm birth (PTB) remains a significant global health challenge. Previous attempts to predict preterm birth in the first trimester using cervical length have been contradictory. The cervical consistency index (CCI) was introduced to quantify early cervical changes and has shown promise across various clinical scenarios in the mid-trimester, though testing in the first trimester is lacking. This study aims to assess the cervical consistency index performance in predicting preterm birth during the first trimester of pregnancy. Methods: In this prospective cohort study, focused exclusively on research, women with singleton pregnancies, both with and without a history of spontaneous preterm birth (sPTB), were included. The primary outcome was sPTB before 37 weeks, with a secondary outcome of sPTB before 34 weeks. CCI measurements were taken between 11+0 to 13+6 weeks of gestation. Receiver operating characteristic (ROC) curves were generated, and sensitivity and specificity were calculated for the optimal cut-off and for the 5th, 10th, and 15th percentile. Intraobserver and interobserver agreements were assessed using the intraclass correlation coefficient (ICC). Results: Among the 667 patients analyzed, the rates of sPTB before 37 and 34 weeks were 9.2% (61/667) and 1.8% (12/667), respectively. The detection rates (DRs) for CCI predicting PTB before 37 and 34 weeks were 19.7% (12/61) and 33.3% (4/12). Negative predictive values were 91.8% (546/595) and 98.7% (588/596), while the areas under the curve (AUC) for sPTB before 37 and 34 weeks were 0.62 (95% CI: 0.54-0.69) and 0.80 (95% CI: 0.71-0.89), respectively. Of the 61 patients with preterm birth, 13 (21.3%) had a preterm birth history; in this group, the CCI percentile 10th identified 39% (5/13). Intraobserver ICC was 0.862 (95% CI: 0.769-0.920), and interobserver ICC was 0.833 (95% CI: 0.722-0.902). Conclusions: This study suggests that utilizing CCI in the first trimester of pregnancy could serve as a valuable tool for predicting preterm birth before 34 weeks of gestation, demonstrating robust intraobserver and interobserver reliability.

First-trimester and early-second-trimester transvaginal cervical length before 16 weeks among women with preterm and term birth: a systematic review and meta-analysis

OBJECTIVE

This study aimed to evaluate the differences in first-trimester and early-second-trimester transvaginal cervical length between patients with spontaneous preterm birth and those with term birth.

DATA SOURCES

PubMed, MEDLINE, Embase, and the Cochrane Library were systematically searched through August 2023.

STUDY ELIGIBILITY CRITERIA

Studies had to include (1) transvaginal cervical length measurement before 16+0 weeks of gestation and (2) transvaginal cervical length measurement in a population of patients who delivered preterm and at term. Abstracts, studies with duplicated data, and those with cervical length measured by transabdominal ultrasound scan were excluded.

METHODS

K.W.C. and J.L. searched for, screened, and reviewed the articles independently. The quality of the studies was assessed using the Newcastle-Ottawa scale. Mean differences were calculated using a random-effects model and pooled through a meta-analysis.

RESULTS

A total of 5727 published articles were identified. Only 10 studies (which analyzed 22,151 pregnancies) met the inclusion criteria. All studies excluded iatrogenic preterm birth. Transvaginal cervical length was significantly shorter in women with spontaneous preterm birth than in those who delivered at term (mean difference, -0.97; 95% confidence interval, -1.65 to -0.29; P=.005; I2=69%). When a linear technique was used to measure transvaginal cervical length, a significantly shorter transvaginal cervical length was associated with spontaneous preterm birth as opposed to term birth (mean difference, -1.09; 95% confidence interval, -1.96 to -0.21; P=.02; I2=77%). A shorter transvaginal cervical length measured by other techniques was also associated with spontaneous preterm birth before 34 to 35 weeks (mean difference, -1.87; 95% confidence interval, -3.04 to -0.70; P=.002; I2=0%). When studies where interventions were given for a "short" cervix or studies with a mean transvaginal cervical length ≥40 mm were excluded, a significantly shorter transvaginal cervical length was observed among those with spontaneous preterm birth (mean difference, -1.13; 95% confidence interval, -1.89 to -0.37; P=.004; mean difference, -0.86; 95% confidence interval, -1.67 to -0.04; P=.04; respectively). The optimal transvaginal cervical length cutoff was 38 to 39 mm, yielding pooled sensitivity of 0.80, specificity of 0.45, positive likelihood ratio of 1.16, negative likelihood ratio of 0.33, diagnostic odds ratio of 5.12, and an area under the curve of 0.75.

CONCLUSION

Women with spontaneous preterm birth had significantly shorter transvaginal cervical length before 16 weeks of gestation compared with those who delivered at term. The linear method and the 2-line method are acceptable techniques for measuring transvaginal cervical length.

Prediction of Preterm Birth with the Uterocervical Angle in Singleton Pregnancies Treated with a Cervical Pessary

BACKGROUND

Cervical pessaries are an established therapy option for patients at risk for spontaneous preterm birth (sPTB). The uterocervical angle (UCA) remains a promising sPTB predictor. However, its clinical significance has yet to be described in patients treated with a pessary.

METHODS

This study analyzed data of patients treated with a pessary because of cervical shortening in singleton pregnancies. The patients were divided into 2 groups according to transvaginal ultrasound findings: the funneling group (n = 68) and the no-funneling group (n = 42). Moreover, we analyzed patients within these prespecified groups according to the UCA < 95° and ≥ 95°.

RESULTS

Delivery occurred significantly earlier in patients treated with a pessary and with a high UCA ≥ 95°(p = 0.006). The median gestational age at delivery in patients treated with a pessary and with no funneling and a UCA < 95° vs. ≥ 95° were 39.00 and 36.14 weeks, respectively (p = 0.005). In cases with funneling and a UCA < 95° vs. ≥ 95° the mean gestational age at delivery was 38.14 and 38.07 weeks respectively (p=1,00). There was a significant negative linear correlation between UCA and the gestational age at delivery in all patients (p = 0.04), which was even profound in the group without funneling (p = 0.0002). However, we found no significant correlation between cervical length and gestational age at delivery in all patients (p = 0.42) as well as in the group without funneling (p = 0.28).

CONCLUSION

In spite of pessary treatment, patients with UCA ≥ 95° presented with a higher risk of sPTB compared to patients with UCA < 95°. This suggests that the UCA seems to be a better predictor of sPTB than the cervical length in patients receiving pessary treatment.

Screening vs. no screening for preterm delivery in low-risk singleton pregnancies: comparison by propensity score analysis

PURPOSE

To compare the effect of a policy of screening for spontaneous preterm delivery (SPD) by transvaginal cervical length (CL) measurement versus a no screening policy in the prevention of severe prematurity.

METHODS

Retrospective study on low-risk singleton pregnancies examined at 20-24 weeks. Two cohorts, one with SPD screening and the other without screening, were matched using propensity analysis to create the study groups. Women with short CL were treated with vaginal progesterone and/or cervical cerclage/pessary. The outcomes examined were SPD < 32 weeks (SPD 32) and SPD between 20 and 32 weeks (SPD 20-32).

RESULTS

Screening for SPD was associated with a significant reduction in the rate of SPD at less than 32 weeks (0.3 vs. 0.8%, p = 0.001 in the screened and no screened pregnancies, respectively) and in the rate of SPD 20-32 (0.3 vs. 0.9%, p = 0.005 in the screened and no screened pregnancies, respectively). After adjusting for maternal age, parity, body mass index, smoking and mode of conception, the screening group had significantly lower hazard for SPD 20-32 (HR = 0.36, 95% CI: 0.18-0.75, p = 0.006) and SPD32 (HR = 0.39, 95% CI: 0.19-0.82, p = 0.013).

CONCLUSION

Screening for SPD by transvaginal CL measurement in mid-pregnancy may reduce the incidence of severe prematurity in low-risk singleton pregnancies.

Maternal Characteristics, Short Mid-Trimester Cervical Length, and Preterm Delivery

We aimed to determine the maternal characteristics (demographics, an obstetric history, and prior cervical excisional procedure) associated with a short mid-trimester cervical length (CL, defined as a CL of ≤ 25 mm) and whether having a short cervix explains the association between these maternal characteristics and spontaneous preterm delivery (SPTD, defined as a delivery before 34 weeks). This is a single-center retrospective cohort study of 3,296 consecutive women with a singleton pregnancy who underwent routine CL measurement between 20 and 24 weeks. Data were collected on maternal age, weight, height, parity, obstetric history (nulliparity; a history of at least 1 SPTD; and at least 1 term birth and no preterm birth [low-risk history group]), and prior cervical excisional procedure. In the multivariate regression analysis, an obstetric history, prior cervical excisional procedure, and gestational age at measurement were the variables significantly associated with short CL. In contrast, maternal weight, height, age, and parity were not significantly associated with short CL. By using the likelihood of SPTD as an outcome variable, logistic regression indicated that short CL and obstetric history, but not prior cervical excisional procedure, were significantly associated with SPTD after adjustment for potential confounders. A history of SPTD and prior cervical excisional procedure were associated with an increased risk of a short mid-trimester CL. A history of SPTD, but not prior cervical excisional procedure, is associated with an increased risk of SPTD, independent of a short CL.

Prognostic models in obstetrics: available, but far from applicable

Health care provision is increasingly focused on the prediction of patients' individual risk for developing a particular health outcome in planning further tests and treatments. There has been a steady increase in the development and publication of prognostic models for various maternal and fetal outcomes in obstetrics. We undertook a systematic review to give an overview of the current status of available prognostic models in obstetrics in the context of their potential advantages and the process of developing and validating models. Important aspects to consider when assessing a prognostic model are discussed and recommendations on how to proceed on this within the obstetric domain are given. We searched MEDLINE (up to July 2012) for articles developing prognostic models in obstetrics. We identified 177 papers that reported the development of 263 prognostic models for 40 different outcomes. The most frequently predicted outcomes were preeclampsia (n = 69), preterm delivery (n = 63), mode of delivery (n = 22), gestational hypertension (n = 11), and small-for-gestational-age infants (n = 10). The performance of newer models was generally not better than that of older models predicting the same outcome. The most important measures of predictive accuracy (ie, a model's discrimination and calibration) were often (82.9%, 218/263) not both assessed. Very few developed models were validated in data other than the development data (8.7%, 23/263). Only two-thirds of the papers (62.4%, 164/263) presented the model such that validation in other populations was possible, and the clinical applicability was discussed in only 11.0% (29/263). The impact of developed models on clinical practice was unknown. We identified a large number of prognostic models in obstetrics, but there is relatively little evidence about their performance, impact, and usefulness in clinical practice so that at this point, clinical implementation cannot be recommended. New efforts should be directed toward evaluating the performance and impact of the existing models.

Cervical length in late second and third trimesters: a mixture model for predicting delivery

OBJECTIVES

To examine the distribution of cervical length (CL) in the late second and third trimesters of pregnancy and construct survival models for spontaneous delivery.

METHODS

This cross-sectional study included 647 women with a singleton pregnancy who had routine CL measurements taken by transvaginal ultrasonography between 24 and 40 weeks' gestation. Only one measurement per patient was included in the analysis. Exploratory data analysis revealed that the distribution of CL measurements was a mixture of two Gaussian distributions, and subsequently a mixture model was applied to describe the distribution of CL. Changes in CL in relation to gestational age were examined by regression analysis and measurements were converted to Z-scores. Survival analysis was applied to the subgroups identified, to describe the probability of delivery throughout gestation.

RESULTS

CL was best described by a mixture model of two subgroups with Gaussian distribution, one including women with a long cervix (73.85% of the study population, mean CL of 28.2 ± 4.45 mm) and the other including women with a short cervix (26.15% of the study population, mean CL of 12.3 ± 5.14 mm). CL was dependent on gestational age (GA), therefore conversion to Z-scores was employed in the analysis. Women with a short cervix had a higher probability for spontaneous delivery (hazard ratio (HR), 1.807; P < 0.001) than did women with a long cervix, after adjustment for GA at the time of measurement (GA HR, 1.115; P < 0.001). In both subgroups, the probability of spontaneous delivery was predicted by the GA and CL Z-scores. Survival models for the prediction of spontaneous delivery were constructed separately for the short-cervix subgroup (GA HR, 1.085; P < 0.001 and CL Z-score HR, 0.819; P = 0.003) and the long-cervix subgroup (GA HR, 1.130; P < 0.001 and CL Z-score HR, 0.864; P = 0.005).

CONCLUSIONS

CL follows a mixture of two Gaussian distributions, one for a short and one for a long cervix. Late second-trimester/third-trimester CL measurement may be of value in estimating the probability for spontaneous delivery at any given gestational age.

In vivo assessment of the biomechanical properties of the uterine cervix in pregnancy

Measuring the stiffness of the cervix might be useful in the prediction of preterm delivery or successful induction of labor. For that purpose, a variety of methods for quantitative determination of physical properties of the pregnant cervix have been developed. Herein, we review studies on the clinical application of these new techniques. They are based on the quantification of mechanical, optical, or electrical properties associated with increased hydration and loss of organization in collagen structure. Quasi-static elastography determines relative values of stiffness; hence, it can identify differences in deformability. Quasi-static elastography unfortunately cannot quantify in absolute terms the stiffness of the cervix. Also, the current clinical studies did not demonstrate the ability to predict the time point of delivery. In contrast, measurement of maximum deformability of the cervix (e.g. quantified with the cervical consistency index) provided meaningful results, showing an increase in compliance with gestational age. These findings are consistent with aspiration measurements on the pregnant ectocervix, indicating a progressive decrease of stiffness along gestation. Cervical consistency index and aspiration measurements therefore represent promising techniques for quantitative assessment of the biomechanical properties of the cervix.

Opening of the uterine isthmus at 11-13 weeks' gestation is not related to developmental abnormalities of the placenta

OBJECTIVES

To clarify whether openning of the uterine isthmus between 11 and 13weeks' gestation adversely affects the placental development.

METHODS

The uterine cervix and isthmus lengths were measured prospectively using transabdominal ultrasound at 11 to 13+6 weeks' gestation. Following delivery, the pregnancy and delivery course were reviewed. The associations between the conditions of the uterine isthmus during the first trimester and the perinatal complications associated with placental abnormalities were analyzed.

RESULTS

A total of 653 cases were analyzed. The isthmus had been completely opened (isthmus length = 0mm) in 15.9%, 21.6% and 24.1% of the cases at 11, 12 and 13 weeks' gestation. The frequencies of perinatal complications in the cases whose isthmus had been opened (cases) and the other cases (controls) were as follows; 1.4% and 1.0% (ns) for placenta previa, 1.4% and 1.2% (ns) for abnormal cord insertion, 3.5% and 4.3% (ns) for pre-eclampsia, 9.9% and 9.0% (ns) for small for gestational age, and 12.0% and 7.6% (ns) for preterm delivery, respectively.

CONCLUSION

Early opening of the uterine isthmus at 11 to 13 weeks' gestation does not appear to adversely affect either the placental development or the course of pregnancy.

Cervical softening occurs early in pregnancy: characterization of cervical stiffness in 100 healthy women using the aspiration technique

OBJECTIVE

To quantitatively describe the evolution of ectocervical stiffness in normal pregnancy.

METHODS

The stiffness of ectocervical tissue was measured by using the aspiration method. This non-invasive technique allows to safely and objectively determine the pressure required to displace cervical tissue to a predefined deformation level (pcl ). In this prospective study, 448 aspiration measurements were carried out on pregnant women (n = 50) at each of the eight routine pregnancy consultations and on nonpregnant subjects (reference, n = 50). pcl values were grouped as nonpregnant, first, second, third trimester, and postpartum.

RESULTS

Stiffness in early pregnancy (first trimester) is significantly lower, by a factor >2 for the mean value than for the nonpregnant group. pcl continuously decreases during gestation, with significant differences between first and second trimester, but not between second and third trimester. After delivery, consistency is recovered to the level of early pregnancy.

CONCLUSIONS

The aspiration method allows an objective description of the consistency of the ectocervix during pregnancy, indicating that the tissue softens already at the beginning of gestation, transforms continuously to lower consistency in the first two trimesters, stabilizes at a low level in the third trimester, and recovers its stiffness after delivery.

Cervical length vs VOCAL cervical volume for predicting pre-term delivery in asymptomatic women at 20-22 weeks' pregnancy

We conducted a prospective observational study of 306 asymptomatic women at 20-22 weeks of pregnancy to compare 3-dimensional ultrasound measurements of cervical volume with 2-dimensional ultrasound measurements of cervical length to evaluate the performance of cervical volume as a predictor of pre-term delivery, compared with the current standard, cervical length. Participants underwent transvaginal ultrasound measurements of cervical length (mm) and cervical volume (cm(3)). Cervical volume as measured by 3-dimensional ultrasound was found to be a useful tool for predicting pre-term delivery; however, due to the high correlation between cervical length and cervical volume and the lack of differences in the sensitivity, specificity, positive predictive value, negative predictive value and relative risk between the two methods, replacing cervical length measurements with cervical volume calculations does not seem to be justified for this purpose, because of increased difficulty in volume acquisition.

Cervical length changes from the first to second trimester of pregnancy, and prediction of preterm birth by first-trimester sonographic cervical measurement

OBJECTIVES

The purpose of this study was to examine the evolution of cervical length from the first to second trimester of pregnancy and the value of first-trimester cervical measurement in the prediction of preterm delivery.

METHODS

We conducted a longitudinal prospective study. Cervical length was measured by transvaginal sonography at 11 to 14 weeks (Cx1), 16 to 19 weeks (Cx2), and 20 to 24 weeks (Cx3).

RESULTS

Eight hundred singleton pregnancies were studied. The median cervical lengths were 33 mm for Cx1 and 31 mm for Cx2 and Cx3. Significant independent predictors for cervical length were maternal weight, height, and history of cervical surgery for Cx1, maternal height, history of cervical surgery, and history of preterm delivery for Cx2, and history of cervical surgery, history of first-trimester miscarriage, and history of spontaneous preterm delivery for Cx3. Mean cervical length shortening was 2.36 mm between Cx1 and Cx3. In the subgroups of women with previous cervical surgery and history of previous preterm birth, cervical shortening was significantly more prominent. The median Cx1 was significantly shorter in the women who subsequently delivered preterm; Cx1 predicted preterm delivery before 34 weeks (odds ratio, 0.746; 95% confidence interval, 0.649-0.869) and preterm delivery before 32 weeks (odds ratio, 0.734; 95% confidence interval, 0.637-0.912).

CONCLUSIONS

Cervical length in the first trimester depends on maternal characteristics and a history of cervical surgery. The cervix exhibits minimal changes from 11 to 24 weeks for most women, although the shortening is more prominent in women with a history of cervical surgery or preterm delivery. First-trimester cervical length measurement can predict preterm delivery.