Comparison of First Trimester Cervical Consistency Index and Cervical Length as a Predictor for Preterm Birth

Abstract

Introduction

Spontaneous preterm birth (sPTB) is a leading cause of neonatal morbidity and mortality. The low sensitivity of short cervical length (CL) for sPTB in low-risk populations highlights the need to explore other predictors. Since cervical softening occurs before its shortening, a marker for cervical compressibility, such as the cervical consistency index (CCI), could improve sPTB prediction.

Objectives

The aim of our study was to evaluate the role of CCI measurement in predicting sPTB in low-risk pregnant women during their first trimester scan. Additionally, CCI's effectiveness was compared with that of CL measured during the same visit. To our knowledge, this is the first study to prospectively assess the ability of the first-trimester (T1) CCI to predict sPTB in a low-risk population.

Methods

Our study was a prospective cohort study that included 518 low-risk singleton pregnancies referred to a single tertiary center (Habashy 4D scan; Alexandria, Egypt) between September 2022 and September 2024. The low-risk population includes individuals without maternal medical disorders, maternal Mullerian anomalies, or a history of sPTB. CL and CCI were measured using transvaginal ultrasound during the T1 scan (11–14 weeks of gestation) from the internal to external os. CL was measured in the sagittal plane without applying probe pressure or fundal pressure. The CCI was calculated as the ratio of the anteroposterior diameter of the cervix at its midpoint under maximal probe pressure (maintained for 10 seconds) to the same diameter without pressure. Cases were then followed by phone calls every 2 weeks until delivery.

Results

A total of 450 cases (87%) delivered full term (≥ 37 weeks). Fifty-seven cases (11%) delivered late preterm (≥ 34 weeks–< 37 weeks). Eleven cases (2%) delivered early preterm (< 34 weeks). The diagnostic performance of T1-CCI surpasses that of T1-CL for predicting sPTB, as the area under the curve for full term versus sPTB and early versus late preterm were 0.858 and 0.738 versus 0.659 and 0.554. The optimal cutoffs for T1-CCI are 75% (for full term vs. preterm) and 67% (for early vs. late preterm). At these cutoffs, T1-CCI shows much higher sensitivity for predicting preterm birth than T1-CL (73.53% vs. 47.06%), with nearly similar specificities (76.89% vs. 83.78%). The specificity of combined T1-CL and T1-CCI is 100%.

Conclusion

The T1-CCI is a better predictor of sPTB before 37 weeks and before 34 weeks than T1-CL in a low-risk population. The optimal cutoffs for T1-CCI are 75% (for full term vs. preterm) and 67% (for early vs. late preterm). The high sensitivity of T1-CCI reduces the false positive rate, thus avoiding unnecessary interventions. Further studies are needed before it can be implemented in routine obstetric practice.

 

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Keywords

cervical consistency index - cervical length - spontaneous preterm birth - first trimester ultrasound

Introduction

Spontaneous preterm birth (sPTB) is defined as delivery before 37 weeks of gestation. It affects about 10% of all deliveries worldwide. Its consequences on neonatal morbidities and mortality are observed in everyday obstetric practice.[1] Cervical length (CL) is a well-established predictor for preterm birth (PTB) for about three decades.[2] The probability of sPTB in those with short cervices at mid-trimester scan is higher in high-risk populations than in low-risk women.[3] [4] [5] [6] [7]

The low sensitivity of short CL at mid-trimester scan for sPTB in low-risk pregnant females makes its value for screening in such populations controversial.[3] [4] [5] [6] [7] On the other hand, the biochemical marker of sPTB (like fetal fibronectin) has low availability and high cost.[8] All of these points warrant further exploration in the pathophysiology of preterm labor as we try to find a more reliable predictor.

It is well known that cervical softening precedes cervical shortening in both term births and PTBs. Cervical softening involves a remodeling of the cervical microstructure, characterized by changes in water content and the alignment of collagen within the cervical stroma. Therefore, methods that detect cervical softening could serve as better predictors for sPTB than CL measurement.[9] [10] [11]

The cervical consistency index (CCI) was first introduced by Parra-Saavedra et al in 2011 as an objective way to assess cervical softness during pregnancy.[12] They measured the percentage of the anteroposterior diameter of the cervix before and at maximum pressure applied with a transvaginal ultrasound (TVUS) probe. They found that CCI is lower in women who deliver preterm compared with those who deliver at term.

CL measurement as a predictor for PTB was first introduced in 1996 and became supported by evidence 20 years later in 2015, after more than 400 publications.[2] [13] On the other hand, CCI has been described for about 15 years, and to this day, fewer than 20 articles have been published about it and it has not yet become established for routine obstetric practice.

Most studies on CL and CCI have evaluated their roles during the mid-trimester scan visit. Few studies have assessed their roles during the first trimester (T1) scan visit.[14] [15] The aim of our study was to evaluate the usefulness of CCI measurement in predicting sPTB in low-risk pregnant women at their T1 scan. Additionally, the effectiveness of CCI was compared with that of CL measured during the same visit.

The primary objective of our study was to evaluate the role of CCI during T1 (T1-CCI) in predicting sPTB before 37 weeks and before 34 weeks of gestation in a low-risk population. The secondary objective was to compare the effectiveness of T1-CCI with that of T1-CL for sPTB prediction. We chose the T1 scan rather than the mid-trimester scan because acceptance of TVUS scanning is higher in the former among our population. To the best of our knowledge, our study is the first to prospectively evaluate the ability of the T1-CCI to predict sPTB in a low-risk population.

 

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Methods

Our study was a prospective cohort involving 518 low-risk pregnant women with singleton pregnancies. It was conducted at a single tertiary center (Habashy 4D scan; Alexandria, Egypt) from September 2022 to September 2024. We used three criteria for including cases: (1) singleton pregnancy, (2) T1 (between 11 and 14 weeks of gestation), and (3) low-risk pregnant women.

To ensure the enrolled cases are from a low-risk population, we applied these 11 exclusion criteria: (1) history of PTB or spontaneous abortion at 16 weeks of gestation or later, (2) cerclage in current or previous pregnancies, (3) maternal medical disorders, especially preeclampsia, thrombophilias, systemic lupus erythematosus, and diabetes mellitus, (4) fetal anomalies, (5) preterm premature rupture of membranes or oligohydramnios, (6) placenta previa, (7) maternal Mullerian anomalies, (8) use of assisted conception, (9) iatrogenic PTB in the current pregnancy, (10) CL of 20 mm or less at enrolment, and (11) spontaneous abortion of the current pregnancy (delivery before 28 weeks of gestation).

At the start of our study, 539 cases had been enrolled. Twenty-one cases were excluded during follow-up; therefore, the total number of cases was 518. The reasons for exclusion after enrolment included: development of preeclampsia (4 cases), development of gestational diabetes mellitus (2 cases), development of preterm premature rupture of membranes (4 cases), diagnosis of fetal gross anomaly (3 cases), undergoing cerclage (91 cases), loss to follow-up (7 cases), having iatrogenic PTB (6 cases), and experiencing spontaneous abortion (4 cases).

All participants provided informed consent before enrolling in our study. The study received approval from the ethical committee for medical research at the Faculty of Medicine, Alexandria University, Alexandria, Egypt. All participants were scanned during the T1 (between 11 and 14 weeks of gestation) using a TVUS probe (RIC5–9A-RS, General Electric GE; Voluson S10-Expert). The scans were performed by Ahmed Elhabashy, an assistant professor of obstetrics and gynecology at Alexandria University and a fellow of Medicina Fetal Barcelona, Spain, who has 15 years of experience in obstetric and gynecological sonography.

CL was measured following this protocol[13]: (1) on the sagittal plane of the cervix, (2) using a zoomed image that fills about two-thirds of the screen, (3) without applying probe or fundal pressure, and (4) measuring from the internal os to the external os with trace calipers in millimeters.

The CCI was measured using the following protocol[12]: (1) follow the first three steps of the CL measurement protocol, (2) measure the anteroposterior diameter of the cervix (in millimeters) perpendicular to its longitudinal axis at the midpoint (this measurement is AP), (3) apply pressure with the probe to the cervix until no more compression is possible, and hold this pressure for 10 seconds, (4) repeat step 2 (i.e. measure the anteroposterior diameter of the cervix in millimeters perpendicular to its longitudinal axis at the midpoint after the 10 seconds of pressure; this measurement is AP'), and (5) calculate the CCI as the result of step 4 (i.e. AP') divided by the result of step 2 (i.e. AP), multiplied by 100, and expressed as a percentage. [Fig. 1] illustrates the steps for measuring CL and CCI.

Fig. 1 The diagram illustrates how to measure the cervical length and the cervical consistency index.

We tracked our cases with phone calls every 2 weeks until delivery. Cases that were lost to follow-up or met any exclusion criteria during their follow-up were excluded from the study.

Statistical Analysis of the Data

The statistical analysis of the data was conducted using IBM SPSS software version 20.0 (IBM Corp, released 2011, Armonk, New York, United States). Categorical data were summarized as counts and percentages. To compare the studied groups, the chi-square test was used. For continuous data, normality was evaluated using the Kolmogorov–Smirnov test. Quantitative data were presented as range, mean, standard deviation, median, and interquartile range. For nonnormally distributed quantitative variables, the Kruskal–Wallis test was employed to compare more than two groups, followed by post hoc analysis using Dunn's multiple comparisons test for pairwise comparisons. A receiver operating characteristic (ROC) curve was generated by plotting sensitivity (true positives, TP) on the Y-axis versus 1-specificity (false positives, FP) on the X-axis at various cutoff values. The area under the ROC curve reflects the diagnostic performance of the test. An area greater than 50% indicates acceptable performance, while an area near 100% signifies excellent performance. The ROC curve also enables comparison of the performance between two tests. The significance level for all statistical tests was set at 5%.

 

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Results

[Table 1] presents the descriptive analysis of the studied cases across various parameters. We classified the cases into three groups based on gestational age at delivery: full-term (≥ 37 weeks), late preterm (34–37 weeks), and early preterm (< 34 weeks). A total of 450 cases (87%) were full-term deliveries (≥ 37 weeks). Fifty-seven cases (11%) were late preterm (≥ 34–< 37 weeks), and 11 cases (2%) were early preterm (< 34 weeks).

Table 1 Descriptive analysis of the cases studied based on various parameters in each group according to GA at delivery

	Total (n = 518)	GA delivery			Test of significance	p
		Full-term (≥ 37) (n = 450) 87%	Preterm (< 34–< 37) (n = 68) 13%
			Late (≥ 34–< 37) (n = 57) 11%	Early (< 34) (n = 11) 2%
Age (y)	20–41	22–39	21–41	20–40	H = 3.453	0.178
Min. – Max.
Mean ± SD	30.47 ± 5.79	30.30 ± 5.85	31.81 ± 5.17	30.91 ± 6.17
Median (IQR)	30 (26–36)	30 (25–35)	32 (28–36)	32 (27–35)
GA US (wk, d)	11 wk 6 d–14 wk	11 wk 6 d–14 wk	12 wk–13 wk 6 d	12 wk 1 d–14 wk	H = 0.265	0.876
Min. – Max.
Mean ± SD	13 wk ± 5 d	13 wk ± 6 d	13 wk ± 4 d	13 wk 4 d ± 4 d
Median (IQR)	13.0 (12 wk 1 d–12 wk 5 d)	13.0 (12 wk 1 d–13 wk 5 d)	13.0 (12 wk 2 d–13 wk 4 d)	13 wk 6 d (12 wk 6 d–13 wk 3 d)
Parity	173 (33.4%)	153 (34.0%)	17 (29.8%)	3 (27.3%)	χ 2 = 0.586	0.7446
P0 (nullipara)
P ≥ 1	345 (66.6%)	297 (66.0%)	40 (70.2%)	8 (72.7%)
BMI (kg/m2)	21–37	23–36	21–34	24–37	H = 0.200	0.905
Min. – Max.
Mean ± SD	29.77 ± 4.62	29.73 ± 4.76	30 ± 3.52	30.35 ± 4.20
Median (IQR)	29.70 (25.60–34)	29.6 (24.8–34.6)	30.40 (27.40–33.10)	29.70 (27.25–33.80)
GA delivery (wk, d)	28 wk–40 wk 5 d	37 wk 1 d–40 wk 5 d	34 wk 1 d–36 wk 4 d	28 wk–33 wk 4 d	H = 178.599[b]	< 0.001[b]
Min. – Max.
Mean ± SD	38 wk 1 d ± 13 d	38 wk 5 d ± 9 d	35 wk 1 d[a] ± 5 d	31 wk 1 d[a] ± 13 d
Median (IQR)	38 wk 2 d (37 wk 1 d–39 wk 4 d)	38 wk 4 d (37 wk 3 d–39 wk 5 d)	35 wk (34 wk 4 d–36 wk)	31 wk 2 d (29 wk 5 d–32 wk 5 d)
T1-CL (mm)	23–42	24–40	23–42	24–39	H = 18.627[b]	< 0.001[b]
Min. – Max.
Mean ± SD	31.08 ± 5.29	31.42 ± 5.22	29.01[a] ± 5.42	27.82[a] ± 4.51
Median (IQR)	30 (27–35)	30.45 (27.10–35.40)	27 (24.40–32)	27 (24–29.5)
T1-CCI	0.66–0.96	0.71–0.96	0.69–0.81	0.66–0.83	H = 91.805[b]	< 0.001[b]
Min. – Max.
Mean ± SD	0.83 ± 0.09	0.84 ± 0.09	0.73[a] ± 0.04	0.70[a] ± 0.06
Median (IQR)	0.83 (0.73–0.92)	0.85 (0.76–0.93)	0.72 (0.69–0.76)	0.67 (0.66–0.73)

Abbreviations: BMI, body mass index; CCI, cervical consistency index; CL, cervical length; GA delivery, gestational age at delivery; GA US, gestational age at the time of ultrasound; IQR, interquartile range; SD, standard deviation; T1, first trimester; χ ², chi-square test.

Note: H: H for Kruskal–Wallis test, pairwise comparisons between each two groups were done using the post hoc test (Dunn's for multiple comparisons).

^a Statistically significant with full-term group.

^b Statistically significant at p ≤ 0.05.

[Table 1] shows that there was no statistically significant difference between the three groups based on maternal age, gestational age at the time of the ultrasound, parity, and body mass index. T1-CL and T1-CCI were significantly lower among cases who delivered preterm (68 cases) than those who delivered at full term (450 cases).

[Fig. 2] shows the ROC curves for T1-CL and T1-CCI. It illustrates the data presented in [Table 2]. ROC curve [Fig. 2A] demonstrates the diagnostic performance of T1-CL and T1-CCI in differentiating preterm cases from full-term cases. ROC curve [Fig. 2B] shows the diagnostic performance of T1-CL and T1-CCI in distinguishing early preterm cases from late preterm cases.

Fig. 2 Receiver operating characteristic (ROC) curves illustrating the performance of first-trimester cervical length (T1-CL) and first-trimester cervical consistency index (T1-CCI). (A) ROC curve for T1-CL and T1-CCI to distinguish preterm cases (n = 68) from full-term cases (n = 450). (B) ROC curve for T1-CL and T1-CCI to differentiate early preterm cases (n = 11) from late preterm cases (n = 57).

Table 2 Diagnostic performance of first trimester cervical length (T1-CL) and first trimester cervical consistency index (T1-CCI) in differentiating preterm cases (n = 68) from full-term cases (n = 450), and early preterm cases (n = 11) from late preterm cases (n = 57)

		AUC	p	95% CI	Cutoff	Sensitivity	Specificity	PPV	NPV
Discriminate all preterm cases (n: 68) from full-term cases (n: 450)	T1-CL	0.659	< 0.001[a]	0.583–0.735	≤ 24 mm	20.59	98.22	63.4	89.11
					≤ 25 mm	32.35	83.78	23.16	89.13
					≤ 26 mm	41.18	100.0	100.0	87.89
					≤ 26.4 mm[b]	47.06	83.78	30.48	91.28
					≤ 27 mm	51.47	75.33	23.97	91.13
	T1-CCI	0.858	< 0.001[a]	0.817–0.900	≤ 0.73	66.18	76.89	30.20	93.77
					≤ 0.74	67.65	76.89	30.67	94.02
					≤ 0.75[b]	73.53	76.89	32.47	95.05
					≤ 0.8	91.18	61.11	26.16	97.86
	T1-CL (≤ 26.4 mm) and T1-CCI (≤ 0.75)					45.59	100.0	100.0	92.4
	T1-CL (≤ 26.4 mm) and/or T1-CCI (≤ 0.75)					75.0	60.67	22.37	94.14
Discriminate late preterm cases (n: 57) from early preterm cases (n: 11)	T1-CL	0.554	0.571	0.384–0.724	≤ 28 mm	63.64	47.37	18.92	87.10
					≤ 29 mm	72.73	40.35	19.05	88.46
					≤ 30 mm	81.82	36.84	20.0	91.30
					≤ 31 mm[b]	90.91	29.82	20.0	94.4
					≤ 32 mm	90.91	24.52	18.87	93.33
	T1-CCI	0.738	0.013[a]	0.521–0.954	≤ 0.66	45.45	100.0	100.0	90.48
					≤ 0.67[b]	63.64	100.0	100.0	93.4
					≤ 0.68	63.64	100.0	100.0	93.44
					≤ 0.69	63.64	73.68	31.82	91.30
					≤ 0.70	63.64	61.40	24.14	89.74

Abbreviations: AUC, area under the curve; CI, confidence interval; NPV, negative predictive value; PPV, positive predictive value.

^a Statistically significant at p ≤ 0.05.

^b Cutoff was chosen according to Youden index.

[Fig. 2] shows that the diagnostic performance of T1-CCI surpasses that of T1-CL in distinguishing cases who will deliver full term from those who will deliver preterm. The T1-CL cannot differentiate between early and late preterm cases, but T1-CCI can distinguish between them. [Fig. 2] provides a graphical representation of the data listed in [Table 2], which displays the areas under the curve (AUCs) of T1-CL and T1-CCI and their diagnostic performances at different cutoffs.

The upper half of [Table 2] showed that the diagnostic performance of T1-CCI in distinguishing between those who will deliver at full term and those who will deliver preterm is better than that of T1-CL, as the AUCs were 0.858 (95% confidence interval [CI]: 0.817–0.90) and 0.659 (95% CI: 0.583–0.735), respectively. The optimal cutoffs based on the ROC curve and Youden index for differentiating between full-term and preterm delivery were 26.4 mm for T1-CL and 0.75 for T1-CCI.

At these cutoffs, the sensitivity of T1-CCI for predicting PTB was much higher than that of T1-CL (73.53% vs. 47.06%), with nearly similar specificities (76.89% vs. 83.78%). The specificity of combined T1-CL and T1-CCI is 100%, meaning that if T1-CL exceeds 26.4 mm and T1-CCI is greater than 0.75, the case is unlikely to deliver preterm.

The lower half of [Table 2] showed that T1-CL is not reliable for distinguishing cases that will deliver early preterm from those that will deliver late preterm, as its AUC was 0.554 (95% CI: 0.384–0.724) and the p-value was 0.571. Conversely, T1-CCI is reliable for making that distinction, with an AUC of 0.738 (95% CI: 0.521–0.954) and a p-value of 0.013.

The optimal cutoff of the T1-CCI based on the ROC curve and Youden index to distinguish between cases that will deliver early preterm from those that will deliver late preterm was 0.67. At this cutoff, the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of T1-CCI were 63.64, 100, 100, and 93.4%, respectively. The cutoffs listed for T1-CL are clinically insignificant because the AUC was low.

From [Table 2], we see that during the TVUS performed in the T1 scan, if the T1-CCI was 0.76 or more, the case is most likely to deliver at or beyond 37 weeks; if the T1-CCI was between 0.68 and 0.75, the case is most likely to deliver late preterm (34–37 weeks); and if the T1-CCI was 0.67 or less, the case is most likely to deliver early preterm (< 34 weeks). These cutoffs are shown in [Table 3].

[Fig. 3] shows examples of normal and abnormal T1-CCI. It depicts two different cases where CCI was measured at the 14th week of gestation.

Fig. 3 Cervical consistency index (CCI) measured in the first trimester (T1) for two different cases at 14 weeks of gestation. (A) Normal T1-CCI > 0.75. (B) Abnormal T1-CCI ≤ 0.75.

Table 3 Cutoffs of the first trimester cervical consistency index (T1-CCI) to predict gestational age (GA) at delivery

Prediction of GA at delivery by first trimester cervical consistency index (T1-CCI) using TVUS
T1-CCI	≥ 0.76	0.68 - 0.75	≤ 0.67
GA at delivery (wk)	≥ 37 wk (full term)	≥ 34–< 37 wk (late preterm)	< 34 wk (early preterm)

Abbreviation: TVUS, transvaginal ultrasound.

 

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Discussion

sPTB is a major cause of neonatal illness and death. The low sensitivity of short CL for predicting sPTB in low-risk groups calls for more research into other predictors. Since cervical softening occurs before its shortening, a marker for cervical flexibility, such as the CCI, might help predict sPTB.

The aim of our study was to assess the role of CCI measurement in predicting sPTB (< 37 and < 34 weeks) in low-risk pregnant women during their T1 scan. Additionally, CCI's effectiveness was compared with that of CL measured during the same visit.

Our study was a prospective cohort that included 518 singleton pregnancies. CL and CCI were measured using TVUS during the T1 scan (11–14 weeks of gestation). CL was measured in the sagittal plane without applying probe pressure or fundal pressure, from the internal to the external os, using trace calipers. The CCI is the ratio of the anteroposterior diameter of the cervix at its midpoint, with maximal probe pressure (maintained for 10 seconds), to the same diameter without probe pressure. Cases were followed up by phone calls every 2 weeks until delivery.

T1-CL and T1-CCI were significantly lower in cases who delivered preterm (68 cases) compared with those who delivered at full term (450 cases). The diagnostic performance of T1-CCI was better than that of T1-CL in distinguishing cases who will deliver at full term from those who will deliver preterm, as shown by the AUCs of 0.858 (95% CI: 0.817–0.90) and 0.659 (95% CI: 0.583–0.735), respectively. The optimal cutoffs based on the ROC curve and Youden index for differentiating between full-term and preterm deliveries were 26.4 mm for T1-CL and 0.75 for T1-CCI.

At these thresholds, the sensitivity of T1-CCI for predicting PTB was significantly higher than that of T1-CL (73.53% vs. 47.06%, respectively), with nearly comparable specificities (76.89% vs. 83.78%). The combined specificity of T1-CL and T1-CCI is 100%, indicating that if T1-CL exceeds 26.4 mm and T1-CCI is greater than 0.75, the case is unlikely to deliver preterm.

The T1-CL is unreliable for distinguishing cases likely to deliver early preterm from those delivering late preterm, with an AUC of 0.554 (95% CI: 0.384–0.724) and a p-value of 0.571. In contrast, T1-CCI is reliable for differentiating between them, showing an AUC of 0.738 (95% CI: 0.521–0.954) and a p-value of 0.013.

The optimal cutoff for the T1-CCI, determined by the ROC curve and Youden index to distinguish between early preterm and late preterm cases, was 0.67. At this cutoff, the sensitivity, specificity, PPV, and NPV of T1-CCI were 63.64, 100, 100, and 93.4%, respectively.

From the data previously mentioned, we can see that during the T1 TVUS scan, if the T1-CCI was 0.76 or more, the case will most likely deliver at 37 weeks or later; if the T1-CCI was between 0.68 and 0.75, the case will mostly deliver late preterm (34–37 weeks); and if the T1-CCI was 0.67 or less, the case will mostly deliver early preterm (< 34 weeks).

Becerra-Mojica et al[14] conducted a prospective study on the performance of T1-CCI to predict sPTB. To our knowledge, this is the only published work on the CCI in the T1. Their study included 667 low-risk singleton pregnancies; 9.2% delivered before 37 weeks and 1.8% delivered before 34 weeks. They found that, at a cutoff of 0.74, the sensitivity of T1-CCI to predict sPTB before 37 weeks was 19.7%, and it was 33.3% for PTB before 34 weeks. The specificity was 90.4% for sPTB before 37 weeks and 90% for sPTB before 34 weeks.

The NPV in their study was 91.8% for sPTB < 37 weeks, and it was 98.7% for sPTB < 34 weeks. The AUC in their study was 0.62 (95% CI: 0.54–0.69) for sPTB < 37 weeks, and it was 0.8 (95% CI: 0.71–0.89) for sPTB < 34 weeks.

Our findings regarding the T1-CCI NPV and AUC were similar to what Becerra-Mojica et al concluded in their study. However, there was a difference between our results and theirs regarding the specificity and sensitivity of T1-CCI for predicting sPTB. This discrepancy can be explained by two reasons. First, we added a step for CCI calculation in our methodology: applying 10 seconds of probe pressure before measuring the AP (the anteroposterior cervical diameter after probe pressure). Additionally, their studied cases included both low-risk and high-risk populations, while our cases were only low-risk.

Becerra-Mojica et al found that the T1-CL showed weak performance in distinguishing cases who will deliver at full term from those who will have sPTB (p-value: 0.843). This finding aligns with our results.

Berghella et al[16] studied 183 high-risk singleton pregnancies to assess the performance of T1-CL in predicting sPTB < 35 weeks. They used CL < 25 mm as the cutoff, similar to what we used in our study. They concluded that the sensitivity, specificity, and NPV of T1-CL < 25 mm were 14, 97, and 82%, respectively. Their results were similar to ours, despite studying a high-risk population.

Antsaklis et al[17] studied 1113 low-risk singleton pregnancies to evaluate T1-CL for predicting sPTB. They used CL < 27 mm as the cutoff. They concluded that the sensitivity, specificity, and NPV of T1-CL < 27 mm for predicting sPTB before 37 weeks were 63, 51, and 91.6%, respectively. The AUC was 0.6 (95% CI: 0.54–0.66). They also concluded that a short cervix (T1-CL < 27 mm) did not have predictive value for PTB before 35 weeks (AUC = 0.55, 95% CI: 0.43–0.65).

Our findings regarding the T1-CL NPV and AUC were similar to what Antsaklis et al concluded in their study. However, there was a discrepancy between our results and theirs in terms of the specificity and sensitivity of T1-CL for predicting sPTB < 37 weeks and < 34 weeks. This discrepancy could be explained by four main factors. First, differences in sample size. Second, we did not use fundal pressure during T1-CL measurement. Third, we used a trace caliper for T1-CL, whereas they used a single-line measurement method. Lastly, we used a 25-mm cutoff for T1-CL, while they used 27 mm.

We have five key strengths in our study. First, to the best of our knowledge, our study is the first to prospectively evaluate the ability of the T1-CCI to predict sPTB in a low-risk population. Our study was designed to screen only low-risk individuals, where it remains debatable whether TVUS CL screening effectively predicts sPTB.

Our study is the first to establish cutoffs of T1-CCI for distinguishing between full-term deliveries and sPTB, as well as between early and late preterm deliveries (0.75 and 0.76, respectively).

Another strength of our study is that we found the sensitivity of the T1-CCI is higher than that of the T1-CL for predicting sPTB (73.53 and 47.06%, respectively). This finding makes this marker (T1-CCI) an important predictor for sPTB. This high sensitivity rate will result in a low FP rate and thus help prevent unnecessary interventions for those with a short CL.

Additionally, the combined use of T1-CL and T1-CCI achieved 100% specificity in our cases. The final strength of our study is that adding a 10-second probe pressure step before measuring P' (P') significantly enhanced the sensitivity of T1-CCI for predicting sPTB compared with previously published literature on the CCI methodology.

The main limitation of our study is the small sample size, which resulted in a low number of preterm deliveries (68 cases). Another limitation is that all cases were scanned by the same sonographer; therefore, more research is needed to assess the reproducibility of CCI measurement among practitioners with different experience levels and to determine interobserver variability. Larger multicenter studies are also necessary before adopting T1-CCI as a prognostic indicator for sPTB in clinical practice.

 

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Conclusion

T1-CCI is a better predictor for sPTB < 37 and < 34 weeks than the T1-CL in a low-risk population. The optimal cutoffs for T1-CCI are 75% (for full term vs. preterm) and 67% (for early vs. late preterm). The high sensitivity of T1-CCI reduces the FP rate, thereby avoiding unnecessary interventions. Further studies are needed before it can be implemented in routine obstetric practice.

 

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Conflict of Interest

None declared.

Ethical Approval

The study was approved by the Institutional Ethics Committee.

• References

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Publikationsverlauf

Artikel online veröffentlicht:
14. Oktober 2025