Gestational age at cervical length measurement and preterm birth in twins

Ultrasonographic cervical length screening at 20-24 weeks of gestation in twin pregnancies for prediction of spontaneous preterm birth: A 10-year Taiwanese cohort

BACKGROUND

Shortened cervical length is one of the primary predictors for spontaneous preterm deliveries in twin pregnancies. However, there is lack of consensus regarding cut-off values. Recent evidence highlights that established cut-offs for cervical length screening might not always apply across different populations. This study aims to present the distribution of cervical length in Taiwanese twin pregnancies and to assess its predictive value for spontaneous preterm birth during mid-trimester screening.

MATERIALS AND METHODS

This retrospective analysis of cervical length screening in Taiwan evaluated 469 twin pregnancies between 20-24 weeks of gestation. Outcome data were obtained directly from the medical records of the delivery hospital. The study explored the predictive value of cervical length screening for spontaneous preterm birth and the characteristics of cervical length distribution in Taiwanese twin pregnancies.

RESULTS

The average gestational age at screening was 22.7 weeks. Cervical length values displayed a non-normal distribution (p-value <0.001). The median, 5th and 95th centiles were 37.5 mm 25.1 mm, and 47.9 mm, respectively. Various cut-off values were assessed using different methods, yielding positive [negative] likelihood ratios for spontaneous preterm births between 32-37 weeks of gestational age (GA) (1.3-30.1 and [0.51-0.92]) and for very preterm births between 28-32 weeks GA (5.6-51.1 and [0.45-0.64]).

CONCLUSIONS

The findings from our analysis of Taiwanese twin pregnancies uphold the moderate predictive potential of cervical length screening, consistent with prior investigations. The presented likelihood ratios for predicting preterm birth at different gestational ages equip clinicians with valuable tools to enhance their diagnostic rationale and resource utilization. By fine-tuning screening parameters according to the spontaneous preterm birth prevalence and clinical priorities of the particular population, healthcare providers can enhance patient care. Our data implies that a cervical length below 20 mm might provide an optimal balance between minimizing false negatives and managing false positives when predicting spontaneous preterm birth.

Cervical pessary for preterm twin pregnancy in women with a short cervix

Objective

We aimed to evaluate the effectiveness of cervical pessary for extending twin pregnancy in women with a short cervix.

Methods

Between January 2014 and March 2019, the use of a cervical pessary for twin pregnancy in women with a cervical length of ≤15 mm was investigated between 16 and 28 weeks of gestation. We included women with a shortened cervix after a cerclage procedure and visible fetal membranes and cervical dilatation. Thirteen patients underwent pessary insertion and were matched with a control group of 15 patients. Pregnancy and neonatal outcomes were compared between the groups. We excluded women with major fetal anomalies discovered before or after birth and known placenta previa.

Results

Women who underwent pessary insertion were diagnosed with a short cervix (0.65±0.47 vs. 0.66±0.51 cm in the pessary and control groups, respectively; P=0.957) at a gestational age similar to that of the controls (23.29 vs. 25.14 weeks, P=0.294). There was no significant difference in gestational age at delivery between them (33.29 vs. 27.29 weeks in the pessary and control groups, respectively, P=0.058). The pessary group had a longer interval between the diagnosis and delivery than the control group (60.7±28.3 vs. 22.6±24.5 days, P=0.001). The number of adverse neonatal outcomes was significantly lower in the pessary group (n=7; 28.0%) than in the control group (n=14; 58.3%; P=0.032).

Conclusion

The use of a cervical pessary may prolong gestation in twin pregnancies in women with an extremely short cervix until viable gestational age.

Short cervical lengths initially detected in mid-trimester and early in the third trimester in asymptomatic twin gestations: Association with histologic chorioamnionitis and preterm birth

Objective

To determine whether short cervical lengths (≤20 mm) that were initially detected in mid-trimester and early in the third trimester are independently associated with increased risks of subsequent histologic chorioamnionitis and spontaneous preterm birth (SPTB, defined as a delivery before 34 weeks) in asymptomatic women with twin pregnancies.

Material and methods

This is a prospective study including 292 consecutive asymptomatic women with twin gestations. Cervical length measurements were carried out at 20 to 24 weeks’ gestation and at 28 to 32 weeks’ gestation. Both placentas of each twin pair were examined histologically after delivery. The generalized estimation equations models and logistic regression analysis were used for statistical analyses.

Results

Multivariable generalized estimation equations analysis revealed that short cervical length at mid-trimester was independently associated with an increased risk for subsequent histologic chorioamnionitis, whereas short cervical length initially detected early in the third trimester was not. By using the likelihood of SPTB as an outcome variable, multivariable logistic regression analysis indicated that short mid-trimester cervical length and histologic chorioamnionitis were independently associated with a greater risk for SPTB. Similarly, based on the multivariable analysis, a short third trimester cervical length was independently and significantly associated with a greater risk for SPTB.

Conclusions

In asymptomatic women with twin pregnancies, a short mid-trimester cervical length is independently associated with an increased risk of both subsequent histologic chorioamnionitis and SPTB, whereas a short cervical length initially detected early in the third trimester is independently associated with preterm delivery, but not subsequent histologic chorioamnionitis.

Association between change in cervical length and spontaneous preterm birth in twin pregnancies

BACKGROUND

There is a lack of consensus on the optimal transvaginal cervical length for determining risk for spontaneous preterm birth in twin pregnancies. Change in transvaginal cervical length over time may reflect early activation of the parturition process, as has been demonstrated in singleton pregnancies. The association between change in transvaginal cervical length and the risk for spontaneous preterm birth has not yet been described in the population of women with diamniotic twin pregnancies.

OBJECTIVE

Our primary objective is to determine whether rate of change in transvaginal cervical length in the midtrimester is associated with spontaneous preterm birth in twin gestations. Our secondary objective is to describe parameters for identifying patients at increased risk for spontaneous preterm birth based on change in transvaginal cervical length over time.

STUDY DESIGN

This is a retrospective cohort of serial transvaginal cervical length performed for twin pregnancies at a single institution from 2008 through 2015. Women with diamniotic twin pregnancies who had transvaginal cervical length measurements at 18 and 22 weeks' gestation and outcome data available were included. Logistic regression was used to determine the relationship between the rate of change in transvaginal cervical length and the risk for the primary outcome of spontaneous preterm birth <35 weeks as well as spontaneous preterm birth <32 weeks.

RESULTS

In all, 527 subjects met inclusion criteria for this study. The average rate of change in transvaginal cervical length for patients with spontaneous preterm birth <35 weeks was -0.21 cm/wk (SD 0.27) vs -0.10 cm/wk (SD 0.24) for patients who delivered ≥35 weeks (P < .01). The rate of change in transvaginal cervical length was associated with spontaneous preterm birth <35 weeks when controlling for initial transvaginal cervical length and other important risk factors for spontaneous preterm birth. Results for spontaneous preterm birth <32 weeks were similar. This association remained significant when the rate of weekly change was treated as a dichotomous variable based on an apparent inflection point in the risk for spontaneous preterm birth: women with rapid change in transvaginal cervical length, ≥-0.2 cm/wk, had 3.45 times the odds of spontaneous preterm birth as those with less rapid change (95% confidence interval, 2.15-5.52) when controlling for initial transvaginal cervical length.

CONCLUSION

Change in transvaginal cervical length in the midtrimester is associated with spontaneous preterm birth, and therefore protocols for serial transvaginal cervical length measurement can provide the clinician with information to identify at-risk patients. A decrease of ≥0.2 cm/wk of transvaginal cervical length identifies patients at increased risk for spontaneous preterm birth <35 weeks.

The effect of gestational age and cervical length measurements in the prediction of spontaneous preterm birth in twin pregnancies: an individual patient level meta-analysis

OBJECTIVE

To assess the effect of gestational age (GA) and cervical length (CL) measurements at transvaginal ultrasound (TVUS) in the prediction of preterm birth in twin pregnancy.

DESIGN

Individual patient data (IPD) meta-analysis.

SETTING

International multicentre study.

POPULATION

Asymptomatic twin pregnancy.

METHODS

MEDLINE and EMBASE searches were performed and IPD obtained from authors of relevant studies. Multinomial logistic regression analysis determined probabilities for birth at ≤28(+0) , 28(+1) to 32(+0) , 32(+1) to 36(+0) , and ≥36(+1) weeks as a function of GA at screening and CL measurements.

MAIN OUTCOME MEASURES

Predicted probabilities for preterm birth at ≤28(+0) , 28(+1) to 32(+0) , and 32(+1) to 36(+0) .

RESULTS

A total of 6188 CL measurements were performed on 4409 twin pregnancies in 12 studies. Both GA at screening and CL had a significant and non-linear effect on GA at birth. The best prediction of birth at ≤28(+0) weeks was provided by screening at ≤18(+0) weeks (P < 0.001), whereas the best prediction of birth between 28(+1) and 36(+0) weeks was provided by screening at ≥24(+0) weeks (P < 0.001). Negative prediction value of 100% for birth at ≤28(+0) weeks is achieved at CL 65 mm and 43 mm at ultrasound GA at ≤18(+0) weeks and at 22(+1) to 24(+0) weeks, respectively.

CONCLUSION

In twin pregnancies, prediction of preterm birth depends on both CL and the GA at screening. When CL is <30 mm, screening at ≤18(+0) weeks is most predictive for birth at ≤28(+0) weeks. Later screening at >22(+0) weeks is most predictive of delivery at 28(+1) to 36(+0) weeks. In twins, we recommend CL screening in twins to commence from ≤18(+0) weeks.

TWEETABLE ABSTRACT

An individual patient meta-analysis assessing gestation and CL in the prediction of preterm birth in twins.

Gestational age at cervical length and fetal fibronectin assessment and the incidence of spontaneous preterm birth in twins

OBJECTIVES

To estimate the risk of spontaneous preterm birth in twin pregnancies based on transvaginal sonographic cervical length, fetal fibronectin (fFN) testing, and the gestational age at which these tests were performed.

METHODS

Women with twin pregnancies, cervical length assessment, and fFN testing between 22 weeks and 31 weeks 6 days in a single maternal-fetal medicine practice from 2005 to 2013 were included. All testing was done on asymptomatic women on an out-patient basis. Women with monochorionic monoamniotic twins and twin-twin transfusion were excluded. Logistic regression analysis was used to estimate the risk of spontaneous preterm birth before 35, 32, and 28 weeks.

RESULTS

Six hundred eleven patients were included and underwent a total of 2406 cervical length measurements and 2279 fFN tests over the course of the study period. The likelihood values for spontaneous preterm birth before 35, 32, and 28 weeks were 19.1%, 6.3%, and 2.3%, respectively. The risk of spontaneous preterm birth before 35 weeks increased with a decreasing cervical length (coefficient for the log of the odds ratio [OR coefficient], -0.13; P < .01; 95% confidence interval [CI], -0.22 to -0.037), a positive fFN result (OR coefficient, 1.04; P < .01; 95% CI, 0.45 to 1.64), as well as earlier gestational ages at testing (OR coefficient, -0.214; P < .01; 95% CI, -0.33 to -0.10). Similar results were seen for spontaneous preterm birth before 32 and 28 weeks.

CONCLUSIONS

In asymptomatic patients with twin pregnancies, the cervical length, fFN, and gestational age are all significantly associated with spontaneous preterm birth.

Efficacy of ultrasound-indicated cerclage in twin pregnancies

OBJECTIVE

We sought to compare the perinatal outcomes in twin pregnancies with short cervical length (CL) with ultrasound-indicated cerclage (UIC) vs no cerclage (control).

STUDY DESIGN

This was a retrospective cohort study of asymptomatic twin pregnancies with transvaginal ultrasound (TVU) CL ≤25 mm at 16-24 weeks from 1995 through 2012 at 4 separate institutions. Exclusion criteria were: genetic or major fetal anomaly, multifetal reduction >14 weeks, monochorionic-monoamniotic placentation, or medically indicated preterm birth (PTB). Primary outcome was spontaneous PTB (SPTB) <34 weeks. Secondary outcome was SPTB <28, <32, and <37 weeks. We also planned to evaluate primary and secondary outcome for the subgroup of twin pregnancies with CL ≤15 mm.

RESULTS

In all, 140 women with twin pregnancy and TVU-CL ≤25 mm were managed with either UIC (n = 57) or no cerclage (n = 83). Demographic characteristics were not significantly different except women who underwent UIC presented at an earlier gestational age (GA) at diagnosis of short CL. After adjusting for GA at presentation, there were no differences in GA at delivery or SPTB <28 weeks: 12 (21.2%) vs 20 (24.1%) (adjusted odds ratio [aOR], 0.3; 95% confidence interval [CI], 0.68-1.37), <32 weeks: 22 (38.6%) vs 36 (43.4%) aOR, 0.34; 95% CI, 0.1-1.13), or <34 weeks: 29 (50.9%) vs 53 (63.9%) (aOR, 0.37; 95% CI, 0.16-1.1). In the subgroup of women with CL ≤15 mm (32 with UIC and 39 controls) the interval between diagnosis to delivery was significantly prolonged by 12.5 ± 4.5 vs 8.8 ± 4.6 weeks (P < .001); SPTB <34 weeks was significantly decreased: 16 (50%) vs 31 (79.5%) (aOR, 0.51; 95% CI, 0.31-0.83) as was admission to neonatal intensive care unit: 38/58 (65.5%) vs 63/76 (82.9%) (aOR, 0.42; 95% CI, 0.24-0.81) when the UIC group was compared with the control group, respectively.

CONCLUSION

UIC in asymptomatic twin pregnancies with TVU-CL ≤25 mm was not associated with significant effects on perinatal outcomes compared to controls. However, in the planned subgroup analysis of asymptomatic twin pregnancies with TVU-CL ≤15 mm before 24 weeks, UIC was associated with a significant prolongation of pregnancy by almost 4 more weeks, significantly decreased SPTB <34 weeks by 49%, and admission to neonatal intensive care unit by 58% compared with controls.

The role of cervical length in women with threatened preterm labor: is it a valid predictor at any gestational age?

OBJECTIVE

To determine whether the predictive accuracy of sonographic cervical length (CL) for preterm delivery (PTD) in women with threatened preterm labor (PTL) is related to gestational age (GA) at presentation.

STUDY DESIGN

A retrospective cohort study of all women with singleton pregnancies who presented with PTL at less than 34 + 0 weeks and underwent sonographic measurement of CL in a tertiary medical center between 2007 and 2012. The predictive accuracy of CL for PTD was stratified by GA at presentation.

RESULTS

Overall, 1077 women who presented with PTL have had sonographic measurement of CL and met the study inclusion criteria. Of those, 223 (20.7%) presented at 24 + 0-26 + 6 weeks (group 1), 274 (25.4%) at 27 + 0-29 + 6 weeks (group 2), 283 (26.3%) at 30 + 0-31 + 6 weeks (group 3), and 297 (27.6%) at 32 + 0-33 + 6 weeks (group 4). The overall performance CL as a predictive test for PTD was similar in the 4 GA groups, as reflected by the similar degree of correlation between CL with the examination to delivery interval (r = 0.27, r = 0.26, r = 0.28, and r = 0.29, respectively, P = .8), the similar area under the receiver-operator characteristic curve (0.641-0.690, 0.631-0.698, 0.643-0.654, and 0.678-0.698, respectively, P = .7), and a similar decrease in the risk of PTD of 5-10% for each additional millimeter of CL. The optimal cutoff of CL, however, was affected by GA at presentation, so that a higher cutoff of CL was needed to achieve a target negative predictive value for delivery within 14 days from presentation for women who presented later in pregnancy. The optimal thresholds to maximize the negative predictive value for delivery within 14 days were 36 mm, 32.5 mm, 24 mm and 20.5 mm for women who presented at 32 + 0 to 33 + 6 weeks, 30 + 0 to 31 + 6 weeks, 27 + 0 to 29 + 6 weeks and 24 + 0 to 26 + 6, respectively.

CONCLUSION

CL has modest predictive accuracy in women with threatened PTL, regardless of GA at presentation. However, the optimal cutoff of CL for the purpose of clinical decision making in women with PTL needs to be adjusted based on GA at presentation.

The association between maternal biomarkers and pathways to preterm birth in twin pregnancies

OBJECTIVE

We sought to estimate the association between cervical length (CL) and fetal fibronectin (fFN) and each pathway leading to preterm birth in twin pregnancies.

METHODS

Cohort study of 560 patients with twin pregnancies who underwent routine serial CL and fFN screening from 22 to 32 weeks in one maternal fetal medicine practice during 2005-2013. We calculated the association between a short CL (≤20 mm) or positive fFN with overall preterm birth <32 weeks, and then subdivided the analysis into preterm birth <32 weeks from preterm labor, preterm premature rupture of membranes (PPROM) and indicated causes. We excluded cases of monochorionic-monoamniotic placentation, vasa previa, twin-twin transfusion and patients with cerclage.

RESULTS

The overall rate of preterm birth <32 weeks was 6.9% (3.9% from preterm labor, 1.6% from PPROM and 1.4% indicated). A short cervix was associated with preterm birth <32 weeks arising from preterm labor (12.4% versus 2.0%, p < 0.001), but not PPROM (1.9% versus 1.3%, p = 0.651). Positive fFN was associated with preterm birth <32 weeks both from preterm labor (17.0% versus 2.4%, p < 0.001) as well as from PPROM (5.7% versus 1.0%, p = 0.034). Neither was significantly associated with preterm birth <32 weeks from indicated causes.

CONCLUSIONS

The mechanism leading toward preterm influences the accuracy of screening tests chosen to assess risk in twin pregnancies. A shortened cervical length and positive fFN is associated with spontaneous preterm labor and birth <32 weeks. However, PPROM does not appear to be preceded by a short cervix, but is preceded by a positive fFN. Neither test is associated with an indicated preterm birth.

The effect of cerclage in twin gestations with short cervix: a Bayesian evaluation

OBJECTIVE

Bayesian inference allows the revision of prior clinical estimates of treatment effectiveness based on current data. We apply it to a published dataset evaluating the effect of cerclage upon preterm delivery in twin gestations with a short cervix.

STUDY DESIGN

Prior probability distributions for delivery <35 weeks gestation for the control group and the treatment (cerclage) group were constructed under assumptions ranging from treatment having no effect (prior A) to halving early deliveries (prior C). Likelihood functions were calculated based on a published meta-analysis. Posterior probability densities were derived from which risk ratios for early delivery were computed, with 95% credible intervals and the probability of cerclage benefit.

RESULTS

Median posterior risk ratios (95% credible intervals) for delivery <35 weeks with cerclage are 1.51 (1.02-2.33) for prior A and 1.11 (0.72-1.77) for prior C. The probability of cerclage benefit ranged from 2.1% for prior A to 31.4% for prior C. By comparison, the conventional risk ratio (95% confidence interval) for early delivery, based on the data alone, is 2.08 (1.18-3.69).

CONCLUSIONS

As might be anticipated, those with low expectation of cerclage benefit remain more convinced of the ineffectiveness (or harm) of the procedure than those with higher expectations.