Transvaginal sonographic cervical length for the prediction of spontaneous preterm birth in twin pregnancies: a systematic review and metaanalysis

Assessment of novel sonographic and biochemical tools for spontaneous preterm birth prediction in asymptomatic twin pregnancies

INTRODUCTION

Prematurity is a major global health issue. Twin pregnancies are a group at especially high risk of preterm birth. Sonographic mid-trimester cervical length has limited accuracy in predicting preterm birth. This study aimed to evaluate the association between mid-trimester sonographic markers of early cervical remodeling and cervical inflammatory biomarkers and fetal fibronectin, alone or in combination, as predictors of preterm birth before 34+0 weeks in asymptomatic twin pregnancies.

MATERIAL AND METHODS

Prospective cohort study, including uncomplicated dichorionic or monochorionic-diamniotic twin pregnancies, recruited and assessed between 18+0 and 24+6 weeks, from a single tertiary referral center between 2020 and 2023. At inclusion, transvaginal ultrasound was performed to assess the following sonographic markers (cervical length, uterocervical angle, cervical consistency index, cervical texture) and an endocervical sample was obtained prior to ultrasound to quantify the following cervical inflammatory biomarkers (tumor necrosis factor alpha, interleukins 1b, 6, 8, 18, matrix metalloproteinase-8 and 9) and fetal fibronectin. The diagnostic performance of those sonographic and biochemical markers independently associated with spontaneous preterm birth before 34 weeks was analyzed by receiver operating characteristic curves and assessed through sensitivity and specificity analysis for several cutoffs.

RESULTS

Of the 172 women included, cervical length was shorter (36 mm vs. 40 mm; p = 0.025) and uterocervical angle was wider (137° vs. 120°; p = 0.004) in the preterm group. Cervical consistency index, cervical texture score, cervical inflammatory biomarkers, and fetal fibronectin were similar among the study groups. The area under the curve to predict spontaneous preterm birth before 34+0 weeks was 0.722 (95% CI 0.577 to 0.866) for cervical length, 0.789 (95% CI 0.683 to 0.895) for uterocervical angle, and 0.852 (95% CI 0.752 to 0.952) for a combination of both. Based on the receiver operating characteristics curve cutoff, sensitivity and specificity for cervical length ≤37 mm was 55.6% and 66.3%, for an uterocervical angle ≥135° was 77.8% and 76.1%, and for both criteria present 44.4% and 93.3%, respectively.

CONCLUSIONS

This finding of this study suggests that the combination of cervical length and uterocervical angle in mid-trimester sonographic assessment may improve the prediction of preterm birth before 34 weeks in asymptomatic and uncomplicated twin pregnancies.

Prevention of preterm birth in twin pregnancy: international Delphi consensus

OBJECTIVE

To use the Delphi method to gain insight into approaches to prenatal diagnosis and management of preterm birth (PTB) in twin pregnancies, including complications such as twin-to-twin transfusion syndrome (TTTS) and a short and/or dilated cervix.

METHODS

A three-round Delphi process was conducted among an international panel of experts to assess their approach to prevention, monitoring and management strategies for PTB in twin pregnancies. Experts were selected based on their publication record or membership of related organizations. Response options were multiple-choice answers or a five-point Likert scale. A priori, a cut-off of ≥ 70% agreement was used to define consensus.

RESULTS

A total of 117 experts participated in the first round, of whom 94/117 (80.3%) completed all subsequent rounds. Representatives came from at least 22 countries (across five continents), most commonly the USA (50.4%) and the UK (12.0%). Over 70% of experts performed routine screening of cervical length (CL) using transvaginal ultrasound at 18-23 weeks' gestation, using CL ≤ 25 mm to diagnose short cervix in twin pregnancies, regardless of a history of PTB. In twin pregnancies with a short non-dilated cervix, most experts offered vaginal progesterone rather than pessary or cervical cerclage, regardless of a history of PTB. In twin pregnancies with asymptomatic dilated cervix, consensus was reached (88.3% agreement) for placement of cervical cerclage, performed up to 24 weeks' gestation (67.5% agreement; no consensus). Similarly, 96.1% of experts agreed that performing serial transvaginal ultrasound measurements of CL at 16-24 weeks' gestation was warranted in women with a current singleton pregnancy who had a previous twin pregnancy that required physical examination-indicated cerclage; these patients should be considered high risk for PTB (83.1% agreement). In twin pregnancies with TTTS, laser surgery is offered by most experts, regardless of preoperative CL. In patients with TTTS and short CL, most experts would recommend cervical cerclage (71.9%) or vaginal progesterone (65.6%) rather than pessary or expectant management. However, no consensus was reached on measures to prevent PTB in cases of TTTS with cervical dilation.

CONCLUSIONS

This Delphi consensus study highlights practice variations among healthcare providers worldwide in the evaluation and management of PTB in twin pregnancies, which often differ from recommendations given by national and international societies. © 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.

Management of twin pregnancies: Remaining challenges and unanswered questions

Several professional societies have published guidelines on twin pregnancies over the past few years. These documents provide recommendations on antenatal surveillance and management of twin pregnancies. At the same time, these guidelines identify several key areas where evidence is limited and additional research is needed. In the present review, we summarize available evidence regarding some of these key areas, including the screening and prevention of preterm birth, the definition and management of fetal growth restriction, the diagnosis and management of gestational diabetes, the optimal maternal gestational weight gain, and the mode and timing of delivery. In addition, we describe several online tools related to these areas that can empower individuals with twin pregnancies and assist care providers in counseling these patients.

Perinatal deaths in twin and singleton infants in Ireland: A comparison of characteristics and causes

INTRODUCTION

Twin pregnancies are associated with significantly higher perinatal mortality (PM) rates compared to singletons, primarily due to complications like fetal growth restriction, preterm birth, and congenital anomalies. This study aimed to compare the characteristics associated with PM in twin pregnancies and compare maternal and obstetric factors and cause of death among twins and singletons in the Republic of Ireland.

MATERIALS AND METHODS

Data spanning 2011 to 2022 from the National Perinatal Epidemiology Centre's annual perinatal mortality clinical audit included 4494 perinatal deaths. Maternal characteristics, antenatal care factors and cause of death were analysed with relative risk calculated using national Hospital In-Patient Enquiry data. Pearson's chi-squared tests studied the difference between mortality in twins and singletons.

RESULTS

Twins accounted for 10.4% of all perinatal deaths, despite representing only 3.6% of total births. The PM rate for twins was 17.3 per 1000 births, 3.1 times higher than for singletons. Early neonatal deaths (ENNDs) were more frequent in twins (54.2%), while stillbirths predominated among singletons (68.6%). Younger maternal age and lower BMI were associated with higher PM risks in twins. A considerable proportion of twin deaths with major congenital anomalies or birth before 28 weeks gestation occurred in non-tertiary hospitals, suggesting limitations in referral pathways to centres with appropriate neonatal expertise.

CONCLUSION

Twin pregnancies pose a higher risk of perinatal mortality, particularly among younger mothers and preterm births. The findings highlight the need for updated guidelines that prioritise early risk assessment, targeted interventions, and improved referral systems.

Cervical cerclage versus cervical pessary with or without vaginal progesterone for preterm birth prevention in twin pregnancies and a short cervix: A two-by-two factorial randomised clinical trial

BACKGROUND

Pregnant women with twins and a short cervical length (CL) are at greater risk of preterm birth (PTB). The comparative efficacy of cervical cerclage and cervical pessary with or without additional progesterone to prevent PTB is unknown. We aimed to assess, in women with twin pregnancies and a short CL, the effectiveness of cerclage versus pessary and the additional treatment with 400 mg vaginal progesterone versus no progesterone in preventing PTB.

METHODS AND FINDINGS

This multicenter, two-by-two factorial randomised trial was conducted in 2 hospitals in Ho Chi Minh City, Vietnam. Asymptomatic women with twin pregnancies and a CL ≤28 mm at 16 to 22 gestational weeks were recruited. Between March 2019 and July 2023, we randomised 219 participants (64.4% of the planned sample size) to cerclage plus progesterone (n = 55), Arabin pessary plus progesterone (n = 56), cerclage alone (n = 54) or Arabin pessary alone (n = 54). Primary outcome was any PTB <34 weeks. Following the second interim analysis, the study was terminated due to significantly lower rates of perinatal deaths and deliveries <28 weeks in the cerclage group. The primary outcome occurred in 20 (19.8%) participants receiving cerclage versus 20 (19%) participants receiving pessary (relative risk [RR] 1.04; 95% confidence interval [CI], 0.60 to 1.8). Delivery <28 weeks occurred in 1% versus 8.6% (RR 0.12; 95% CI, 0.01 to 0.52) and perinatal death occurred in 1% versus 5.8% (RR 0.17; 95% CI, 0.05 to 0.62) in the cerclage group and the pessary group, respectively. However, PTB <24 weeks, <32 weeks, and other neonatal outcomes were not significantly different between the 2 groups. For maternal side effects, vaginal discharge was significantly less frequent in the cerclage group. In participants allocated to progesterone, PTB <34 weeks occurred in 19 (18.4%) versus 21 (20.4%) participants who did not have progesterone (RR 0.90; 95% CI, 0.52 to 1.6).

CONCLUSIONS

In this prematurely halted study on pregnant women with twins and a CL ≤28 mm, cerclage and cervical pessary were comparably effective on PTB <34 weeks prevention. However, compared to pessary, cerclage was associated with significantly lower rates of PTB <28 weeks and perinatal mortality. ClinicalTrials.gov Registration: NCT03863613 (https://clinicaltrials.gov/study/NCT03863613).

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.

Prediction of preterm birth using machine learning: a comprehensive analysis based on large-scale preschool children survey data in Shenzhen of China

BACKGROUND

Preterm birth (PTB) is a significant cause of neonatal mortality and long-term health issues. Accurate prediction and timely prevention of PTB are essential for reducing associated child mortality and morbidity. Traditional predictive methods face challenges due to heterogeneous risk factors and their interaction effects. This study aims to develop and evaluate six machine learning (ML) models to predict PTB using large-scale children survey data from Shenzhen, China, and to identify key predictors through Shapley Additive Explanations (SHAP) analysis.

METHODS

Data from 84,050 mother-child pairs, collected in 2021 and 2022, were processed and divided into training, validation, and test sets. Six ML models were tested: L1-Regularised Logistic Regression, Light Gradient Boosting Machine (LightGBM), Naive Bayes, Random Forests, Support Vector Machine, and Extreme Gradient Boosting (XGBoost). Model performance was evaluated based on discrimination, calibration and clinical utility. SHAP analysis was used to interpret the importance and impact of individual features on PTB prediction.

RESULTS

The XGBoost model demonstrated the best overall performance, with the area under the receiver operating characteristic curve (AUC) scores of 0.752 and 0.757 in the validation and test sets, respectively, along with favorable calibration and clinical utility. Key predictors identified were multiple pregnancies, threatened abortion, and maternal age of conception. SHAP analysis highlighted the positive impacts of multiple pregnancies and threatened abortion, as well as the negative impact of micronutrient supplementation on PTB.

CONCLUSION

Our study found that ML models, particularly XGBoost, show promise in accurately predicting PTB and identifying key risk factors. These findings provide the potential of ML for enhancing clinical interventions, personalizing prenatal care, and informing public health initiatives.

Counselling in Fetal Medicine: Uncomplicated Twin Pregnancies

Twin pregnancies account for 3% of all pregnancies and they are burdened by higher morbidity and mortality compared to singletons. The role of ultrasound in the screening, diagnosis and management of possible complications of twin pregnancies has been widely investigated in the current literature. However, despite the progress that have been made in the last decades regarding treatment and evidence-based management of complications, twin pregnancies remain at higher risk of adverse outcomes, requiring therefore dedicated surveillance. Thorough counselling regarding the risks and prenatal care should be offered to all future parents of twin pregnancies. This review aims to summarize the current evidence regarding the management of uncomplicated dichorionic and monochorionic pregnancies.

Preterm birth in low-middle income Countries

Preterm birth (PTB), remains a major cause of significant morbidity and mortality world-wide with about 12-15million preterm births occurring every year. Although the overall trend is decreasing, this is mainly in high-income countries (HIC). The rate remains high in low-and middle-income countries (LMIC) varying on average between 10 and 12% compared to 9% in HIC. The pathogenesis of PTB is complex and multifactorial. Attempts to reduce rates that have focused on PTB as a single condition have in general been unsuccessful. However, more recent attempts to phenotype PTB have resulted in targeted preventative approaches which are yielding better results. Prevention (primary or secondary) is the only approach that has been shown to make a difference to rates of PTB. These include identifying risk factors pre-pregnancy and during pregnancy and instituting appropriate measures to address these. In LMIC, although some approaches that have been shown to be effective in some HIC are adaptable, there is a need to involve stakeholders at all levels in utilizing evidence preferrably generated in LMIC to implement strategies that are likely to reduce the rate of PTB. In this review, we focus on prevention and how to involve policy makers in the process of applying evidence into policy that would reduce PTB in LMIC.

PROMPT: Prospective Meta-analysis for Pessary Trials Study Protocol

OBJECTIVE

Preterm birth, defined as birth before 37 weeks of gestation, is a leading cause of perinatal and infant mortality throughout the world. Preterm birth is also associated with long-term neurological disabilities and other significant health issues in children. A short cervix in the second trimester has been noted to be one of the strongest predictors of subsequent spontaneous preterm birth in both singleton and multiple pregnancies. Some studies have shown that cervical support in the form of an Arabin pessary lowers the risk of preterm birth in women with a singleton gestation and short cervical length; however, other studies have conflicting results. Our objective was to form an international collaborative of planned or ongoing randomized trials of pessary in singleton and twin gestations with a short cervix.

STUDY DESIGN

In November 2014, an international group of investigators, who had initiated or were planning randomized trials of pessary for pregnant people with a short cervix and singleton or twin gestation to prevent preterm birth, formed a collaboration to plan a prospective individual patient data (IPD) meta-analysis of randomized trials (PROspective Meta-analysis of Pessary Trials [PROMPT]). The PROMPT investigators agreed on meta-analysis IPD hypotheses for singletons and twins, eligibility criteria, and a set of core baseline and outcome measures. The primary outcome is a composite of fetal death or preterm delivery before 32 weeks' gestation. Secondary outcomes include maternal and neonatal morbidities. The PROMPT protocol may be viewed as a written agreement among the study investigators who make up the PROMPT consortium (PROSPERO ID# CRD42018067740).

RESULTS

Results will be published in phases as the individual participating studies are concluded and published. Results of the first phase of singleton and twin pessary trials are expected to be available in late 2022. Updates are planned as participating trials are completed and published.

KEY POINTS

· Short cervical length predicts preterm birth.. · Results of prior cervical pessary trials are mixed.. · Meta-analysis of pessary trials protocol..

The effect of cervical pessary on increasing gestational age at delivery in twin pregnancies with asymptomatic short cervix: a systematic review and meta-analysis of randomized controlled trials

Objective

The incidence of preterm delivery is much higher in twin pregnancies than in singletons and even higher if a short cervical length is detected in the second trimester. Studies are contradictory regarding the efficacy of a cervical pessary to decrease preterm birth in twin pregnancies and short cervical length. To conduct a systematic review and meta-analysis investigating the efficacy of cervical pessary in prolonging gestation, preventing preterm birth, and reducing adverse neonatal outcomes in twin pregnancies with an asymptomatic short cervix.

Data sources

PubMed, Scopus, Web of Science, and ClinicalTrials.org were searched for randomized controlled trials from inception to June 2023.

Study eligibility criteria

In this study, randomized controlled trials comparing the cervical pessary to expectant management in the pregnant population with twin gestations and asymptomatic short cervix were included.

Methods

The Cochrane risk-of-bias-2 tool for randomized controlled trials was used for the evaluation of the risk of bias in included studies. A meta-analysis was performed by calculating risk ratio and mean difference with their 95% confidence interval using the random effects model or fixed effect model on the basis of heterogeneity and accounting for potential covariates among the included randomized controlled trials.

Results

A total of 6 randomized controlled trials were included in the analysis. Cervical pessary did not significantly increase the gestational age at delivery in twin pregnancies with asymptomatic patients (mean difference, 0.36 weeks [-0.27 to 0.99]; P=.270; I2=72.0%). Moreover, the cervical pessary use did not result in a reduction of spontaneous or all-preterm birth before 37 weeks of gestation (risk ratio, 0.88 [0.77-1.00]; P=.061; I2=0.0%). There was no statistically significant difference in the composite neonatal adverse outcomes (risk ratio, 1.001 [0.86-1.16]; P=.981; I2=20.9%), including early respiratory morbidity, intraventricular hemorrhage, necrotizing enterocolitis, and confirmed sepsis.

Conclusion

The use of cervical pessary in twin pregnancies with asymptomatic short cervix does not seem to be effective in increasing the gestational age at delivery, preventing preterm birth, or reducing adverse neonatal outcomes. This indicates that alternative interventions should be sought for the management of this patient population.

Randomized controlled trials: not always the "gold standard" for evidence in obstetrics and gynecology

Randomized controlled trials are considered the "gold standard" for therapeutic interventions, and it is not uncommon for sweeping changes in medical practice to follow positive results from such trials. However, randomized controlled trials are not without their limitations. Physicians frequently view randomized controlled trials as infallible, whereas they tend to dismiss evidence derived from sources other than randomized controlled trials as less credible or reliable. In several situations in obstetrics and gynecology, there are no randomized controlled trials to help guide the clinician. In these circumstances, it is important to evaluate the entire body of evidence including observational studies, rather than dismiss interventions altogether simply because no randomized controlled trials exist. Randomized controlled trials and observational studies should be viewed as complementary rather than at odds with each other. Some reversals in widely adopted clinical practice have recently been implemented following subsequent studies that contradicted the outcomes of major randomized controlled trials. The most notable of these was the withdrawal from the market of 17-hydroxyprogesterone caproate for preterm birth prevention. Such reversals could potentially have been averted if the inherent limitations of randomized controlled trials were carefully considered before implementing these universal practice changes. This Clinical Opinion underscores the limitations of an exclusive reliance on randomized controlled trials while disregarding other evidence in determining how best to care for patients. Solutions are proposed that advocate that clinicians adopt a more balanced perspective that considers the entirety of the available medical evidence and the individual patient characteristics, needs, and wishes.

Utility of cervical pessary in the prevention of preterm birth in triplet pregnancies: A single-center observational retrospective study of 165 triplet pregnancies

OBJECTIVE

Premature births are a health problem arising in triplet pregnancies, resulting in high levels of morbidity and mortality. The objective of this study is to evaluate the utility of cervical pessaries in reducing prematurity (<34 weeks) in triplet pregnancies.

METHODS

This is a single-center, retrospective case-control study regarding triplet pregnancies with follow-up at the La Paz University Hospital between 2000 and 2023. Maternal characteristics, obstetric and perinatal outcomes, and the use of cervical pessaries were examined.

RESULTS

165 triplet pregnancies were analyzed: 87 (52.7 %) in the case group (premature triplet pregnancies) and 78 in the control group (non-premature triplet pregnancies). A cervical pessary was inserted in 15 (17.2 %) triplet pregnancies in the case group and in 12 (16.7 %) triplet pregnancies in the control group (p = 0.92; OR = 1.04 (0.46-2.35)). A pessary was later inserted in the non-premature group (p = 0.01). The risk of preterm labor and the use of tocolytics ± glucocorticoids were found to be significantly more frequent in the premature group, with p = 0.01; OR = 2.30 (1.21-4.36) and p < 0.01; OR = 2.36 (1.23-4.44), respectively. Protocol-based cesarean sections were more frequent in the non-premature group (p < 0.01), while cesarean sections due to maternal complications (p < 0.01) and premature membrane rupture (p < 0.01) were more frequent in the premature group.

CONCLUSION

The cervical pessary is not useful in preventing preterm births (< 34 weeks) in triplet pregnancies. It is likely that being pregnant with triplets is a powerful independent factor associated with prematurity, despite other pregnancy conditions. Women who are pregnant with triplets and at risk of preterm labor and those taking tocolytics ± glucocorticoids may benefit from pessary insertion.

Cervical assessment certification and its impact on performance quality in the context of universal cervical screening

OBJECTIVE

To assess the impact of the introduction of universal transvaginal cervical screening and certification on the quality of cervical length ultrasound images.

METHODS

The present study included a retrospective cohort of singleton pregnancies that underwent transvaginal cervical length measurement at the anatomical scan (180/7 and 236/7 weeks) before (period A, 2015-2017) and after (period B, 2017-2019) the introduction of universal transvaginal cervical length screening. Independent observers blindly evaluated the images obtained for cervical length using a qualitative scoring method based on five criteria, according to the Fetal Medicine Foundation.

RESULTS

In all, 6013 patients met the inclusion criteria, 3333 in period A and 2680 in period B. Maternal characteristics and risk factors for preterm birth were similar between the two periods. The acceptance of transvaginal cervical length measurement in period B was 95.5% in the overall cohort and 100% in the subgroup of high-risk patients. The quality score was significantly higher in period B than in period A. Among the image quality criteria, the anterior/posterior ratio, the correct magnification of the images, and the calipers' placement contributed significantly to the improved quality score in period B. Most of the sonographers performed better in period B, irrespective of the years of experience, but certificate holders obtained higher scores than non-certified sonographers, particularly those in mid-career. The identification of short cervix was significantly higher in period B than in period A.

CONCLUSION

The implementation of universal transvaginal cervical length screening and the certification process are associated with improved quality of cervical length images, even among expert sonographers and in the presence of anatomical pitfalls.

Management of short cervix in twin-to-twin transfusion syndrome: a role for pessary placement following fetoscopic laser surgery?

BACKGROUND

Preterm labor and delivery is a major concern for patients with twin-to-twin transfusion syndrome undergoing fetoscopic laser surgery. A preoperative short cervix is a risk factor for preterm labor. Pessary placement is a short-acting intervention that may be useful to reduce this adverse event.

OBJECTIVE

This study aimed to investigate the relationship between pessary placement and preterm delivery in monochorionic twin pregnancies with twin-to-twin transfusion syndrome and a short cervix before fetoscopic laser surgery.

STUDY DESIGN

This was a retrospective study in 2 centers, including all pregnancies affected by twin-to-twin transfusion syndrome that underwent fetoscopic laser surgery with the Solomon technique between 2013 and 2022 (center A) and 2014 and 2022 (center B) with a preoperative cervical length below 25 mm. This study explored the correlation between cervical length and fetoscopic laser surgery-to-delivery interval following active or expectant management and compared perinatal outcomes between patients managed expectantly and patients managed with pessary placement, using multivariate analysis to control for potential confounders. Patients with a cervical length below 5 mm were not included in the comparative analysis.

RESULTS

Of 685 patients, 134 met the inclusion criteria. Moreover, 21 patients were treated with a cervical cerclage and excluded from the analysis, leaving 113 patients for the final analysis. There was a significant negative correlation between cervical length at fetoscopic laser surgery and the risk of early delivery (adjusted odds ratio, 0.66; 95% confidence interval, 0.49-0.81; P<.001). The use of a pessary correlated with fewer patients delivering before 28 weeks of gestation (adjusted odds ratio, 0.28; 95% confidence interval, 0.09-0.75), fewer double neonatal demise (adjusted odds ratio, 0.2; 95% confidence interval, 0.05-0.75). Posthoc subgroup analysis suggested that these improvements were essentially noticeable for cervical lengths between 5 and 18 mm, where pessary placement was associated with an increased fetoscopic laser surgery-to-delivery interval (+24 days; 95% confidence interval, 0.86-42; P=.042) and later gestational age at delivery (+3.3 weeks; 95% confidence interval, 0.86-42; P=.035).

CONCLUSION

Patients with a moderately shortened cervix, between 5 and 18 mm, may benefit from pessary placement after fetoscopic surgery for twin-to-twin transfusion syndrome, resulting in a reduction of adverse neonatal outcomes, double neonatal demise, and severe preterm delivery.

Prevention of spontaneous preterm delivery – an update on where we are today

Spontaneous preterm birth (delivery before 37 completed weeks) is the single most important cause of perinatal morbidity and mortality. The rate is increasing world-wide with a great disparity between low, middle and high income countries. It has been estimated that the cost of neonatal care for preterm babies is more than 4 times that of a term neonate admitted into the neonatal care. Furthermore, there are high costs associated with long-term morbidity in those who survive the neonatal period. Interventions to stop delivery once preterm labor starts are largely ineffective hence the best approach to reducing the rate and consequences is prevention. This is either primary (reducing or minimizing factors associated with preterm birth prior to and during pregnancy) or secondary - identification and amelioration (if possible) of factors in pregnancy that are associated with preterm labor. In the first category are optimizing maternal weight, promoting healthy nutrition, smoking cessation, birth spacing, avoidance of adolescent pregnancies and screening for and controlling various medical disorders as well as infections prior to pregnancy. Strategies in pregnancy, include early booking for prenatal care, screening and managing medical disorders and their complications, and identifying predisposing factors to preterm labor such as shortening of the cervix and timely instituting progesterone prophylaxis or cervical cerclage where appropriate. The use of biomarkers such as oncofetal fibronectin, placental alpha-macroglobulin-1 and IGFBP-1 where cervical screening is not available or to diagnosis PPROM would identify those that require close monitoring and allow the institution of antibiotics especially where infection is considered a predisposing factor. Irrespective of the approach to prevention, timing the administration of corticosteroids and where necessary tocolysis and magnesium sulfate are associated with an improved outcome. The role of genetics, infections and probiotics and how these emerging dimensions help in the diagnosis of preterm birth and consequently prevention are exciting and hopefully may identify sub-populations for targeted strategies.

Preterm Birth: Screening and Prediction

Preterm birth (PTB) affects approximately 10% of births globally each year and is the most significant direct cause of neonatal death and of long-term disability worldwide. Early identification of women at high risk of PTB is important, given the availability of evidence-based, effective screening modalities, which facilitate decision-making on preventative strategies, particularly transvaginal sonographic cervical length (CL) measurement. There is growing evidence that combining CL with quantitative fetal fibronectin (qfFN) and maternal risk factors in the extensively peer-reviewed and validated QUanititative Innovation in Predicting Preterm birth (QUiPP) application can aid both the triage of patients who present as emergencies with symptoms of preterm labor and high-risk asymptomatic women attending PTB surveillance clinics. The QUiPP app risk of delivery thus supports shared decision-making with patients on the need for increased outpatient surveillance, in-patient treatment for preterm labor or simply reassurance for those unlikely to deliver preterm. Effective triage of patients at preterm gestations is an obstetric clinical priority as correctly timed administration of antenatal corticosteroids will maximise their neonatal benefits. This review explores the predictive capacity of existing predictive tests for PTB in both singleton and multiple pregnancies, including the QUiPP app v.2. and discusses promising new research areas, which aim to predict PTB through cervical stiffness and elastography measurements, metabolomics, extracellular vesicles and artificial intelligence.

Development and validation of a prediction model on spontaneous preterm birth in twin pregnancy: a retrospective cohort study

BACKGROUND

This study was conducted to develop and validate an individualized prediction model for spontaneous preterm birth (sPTB) in twin pregnancies.

METHODS

This a retrospective cohort study included 3845 patients who gave birth at the Chongqing Maternal and Child Health Hospital from January 2017 to December 2022. Both univariable and multivariable logistic regression analyses were performed to find factors associated with sPTB. The associations were estimated using the odds ratio (OR) and the 95% confidence interval (CI). Model performance was estimated using sensitivity, specificity, accuracy, area under the receiver operating characteristic curve (AUC) and decision curve analysis (DCA).

RESULTS

A total of 1313 and 564 cases were included in the training and testing sets, respectively. In the training set, univariate and multivariate logistic regression analysis indicated that age ≥ 35 years (OR, 2.28; 95% CI 1.67-3.13), pre-pregnancy underweight (OR, 2.36; 95% CI 1.60-3.47), pre-pregnancy overweight (OR, 1.67; 95% CI 1.09-2.56), and obesity (OR, 10.45; 95% CI, 3.91-27.87), nulliparity (OR, 0.58; 95% CI 0.41-0.82), pre-pregnancy diabetes (OR, 5.81; 95% CI 3.24-10.39), pre-pregnancy hypertension (OR, 2.79; 95% CI 1.44-5.41), and cervical incompetence (OR, 5.12; 95% CI 3.08-8.48) are independent risk factors for sPTB in twin pregnancies. The AUC of the training and validation set was 0.71 (95% CI 0.68-0.74) and 0.68 (95% CI 0.64-0.73), respectively. And then we integrated those risk factors to construct the nomogram.

CONCLUSIONS

The nomogram developed for predicting the risk of sPTB in pregnant women with twins demonstrated good performance. The prediction nomogram serves as a practical tool by including all necessary predictors that are readily accessible to practitioners.

Value of post-cerclage transvaginal ultrasound in predicting preterm birth at <28 weeks in twin pregnancy with ultrasound-indicated cerclage

OBJECTIVE

To evaluate the value of transvaginal ultrasound parameters before and after cerclage in twins in predicting spontaneous preterm birth (sPTB) before 28+0 weeks.

METHODS

We retrospectively studied the medical records of twin-pregnant women who underwent ultrasound-indicated cerclage between January 2016 and February 2022 at our hospital. Recorded transvaginal ultrasound images before and after cerclage were reassessed for cervical length (CL), uterocervical angle (UCA), funneling, and sludge. Multivariate logistic and Cox regression analyses were performed to identify the independent risk factors associated with sPTB before 28 weeks.

RESULTS

A total of 69 women were included. Among them, 17 women (24.64%) delivered before 28 weeks of age. Regression analysis revealed a significant association of post-cerclage CL, UCA, white blood cell (WBC) count, and gestational age (GA) at cerclage with sPTB before 28 weeks. The area under the curve of these predictors was 0.938 (95% confidence interval, 0.882-0.994; p < .001), with a sensitivity of 88.2%, specificity of 92.3%, positive predictive value of 78.9%, and negative predictive value of 96.0%. Cox analysis showed that post-cerclage UCA was an independent risk factor affecting the cerclage-to-delivery interval (hazard ratios, 1.026; 95% confidence interval (CI), 1.004-1.048; p = .019).

CONCLUSIONS

The combination of post-cerclage CL, UCA, WBC count, and GA at cerclage showed good performance in predicting sPTB at <28 weeks in twin pregnancy. Post-cerclage UCA is also associated with pregnancy latency. We found that post-cerclage cervical ultrasound may be useful to predict preterm birth before 28 weeks in twins who undergo ultrasound-indicated cerclage.

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 sliding sign at second trimester in the prediction of early preterm birth in twin pregnancy

OBJECTIVE

To examine the cervical sliding sign (CSS) alongside cervical length (CL) in twin pregnancies to predict preterm birth (PB).

METHODS

Twin pregnancies (n = 37) with no known risk factor for PB were included in this prospective study. CSS was defined as the ultrasonographic finding in which the anterior lip of the cervix slides over the posterior lip with gentle and continuous pressure application. The CSS and CL measurements were held in the second trimester. Early PB was defined as the birth of the fetus before 32 weeks of gestation. The patients were divided into two groups as CSS-positive and CSS-negative.

RESULTS

Whereas 11 (29.7%) of the twin pregnancies were CSS-positive, 26 (70.3%) were CSS-negative. CSS positivity had a sensitivity of 75.0%, a specificity of 82.2%, a positive predictive value of 54.5%, and a negative predictive value of 92.3% to predict early PB. Multivariate logistic regression analysis revealed that CSS positivity was the only significant independent factor related to early PB.

CONCLUSION

CSS was shown to be superior to CL in providing a better insight to predict early PB. CSS evaluation should be performed in twin pregnancies.

The use of cervical cerclage in asymptomatic twin pregnancies with cervical shortening or dilation: a twelve-year retrospective cohort study

BACKGROUND

To identify the effect and optimal time of cervical cerclage in asymptomatic twin pregnancies with cervical shortening or dilation.

METHODS

This observational retrospective study enrolled all women with asymptomatic twin pregnancies who were diagnosed with asymptomatic cervical shortening or dilation at the Second Affiliated Hospital of Wenzhou Medical University between 2010 and 2022. Women included were allocated into the cerclage group (n = 36) and the no cerclage group (n = 22). The cerclage group was further divided into the cerclage group (< 24 weeks group) and the cerclage group (24-28 weeks group) according to the time of cerclage. The no cerclage group was further divided into no cerclage group (< 24 weeks group) and no cerclage group (24-28 weeks group) according to the time of ultrasound-indicated or physical exam indicated cerclage. The rates of PTB < 24, 28, 32 and 34 weeks of gestation, maternal and neonatal outcomes were compared among the groups.

RESULTS

The gestational age (GA) at delivery was higher (P = 0.005) and the interval time between the presentation of the indicated cerclage and delivery was longer in the cerclage group (P < 0.001). The rates of PTB before 28, 32, and 34 weeks of gestation, caesarean section and stillbirth were lower in the cerclage group (P < 0.05). The birthweight of the twins was higher in the cerclage group (P = 0.012). Admissions to the NICU were more frequent in pregnancies with no cerclage (P = 0.008). Subgroup analysis showed that the interval time between the presentation and delivery was longer in the cerclage group (< 24 weeks) (P < 0.001). The GA at delivery and the birthweight of the twins were significantly higher in the cerclage group (< 24 weeks) (P < 0.001). No differences were found in the GA at presentation, the GA at delivery, the interval time between the presentation to delivery and birthweight between the cerclage group (24-28 weeks group) and the control group (24-28 weeks group) (P > 0.05).

CONCLUSIONS

Cerclage appears to prolong the GA at delivery and the interval time between the presentation to delivery, and may reduce the incidence of PTB before 28, 32 and 34 weeks of gestation and adverse perinatal outcomes in asymptomatic twin pregnancies with cervical shortening or dilation. Cerclage before 24 weeks of gestation showed longer GA at delivery, longer interval time between the presentation to delivery and higher birthweight of the twins. The GA at presentation, the GA at delivery, the interval time between the presentation to delivery and birthweight in women with cerclage at 24-28 weeks were similar to those in women without cerclage at 24-28 weeks.

How to screen the cervix and reduce the risk of spontaneous preterm birth in asymptomatic women without a prior preterm birth

Preterm birth (PTB) is a leading cause of perinatal morbidity and mortality globally. PTB rates have increased in South Korea despite reduction in birth rates. A history of PTB is a strong predictor of subsequent PTB and screening of cervical length between 16 0/7 weeks and 24 0/7 weeks of gestation is recommended in women with a singleton pregnancy and a prior spontaneous PTB. However, the prediction and prevention of spontaneous PTBs in women without a prior PTB remain a matter of debate. The scope of this review article comprises cervical screening and prevention strategies for PTB in asymptomatic women without a prior PTB, based on recent evidence and guidelines.

Cervical cerclage for prevention of preterm birth and adverse perinatal outcome in twin pregnancies with short cervical length or cervical dilatation: A systematic review and meta-analysis

BACKGROUND

The optimal approach to prevent preterm birth (PTB) in twins has not been fully established yet. Recent evidence suggests that placement of cervical cerclage in twin pregnancies with short cervical length at ultrasound or cervical dilatation at physical examination might be associated with a reduced risk of PTB. However, such evidence is based mainly on small studies thus questioning the robustness of these findings. The aim of this systematic review was to determine the role of cervical cerclage in preventing PTB and adverse maternal or perinatal outcomes in twin pregnancies.

METHODS AND FINDINGS

Key databases searched and date of last search: MEDLINE, Embase, and CINAHL were searched electronically on 20 April 2023. Eligibility criteria: Inclusion criteria were observational studies assessing the risk of PTB among twin pregnancies undergoing cerclage versus no cerclage and randomized trials in which twin pregnancies were allocated to cerclage for the prevention of PTB or to a control group (e.g., placebo or treatment as usual). The primary outcome was PTB <34 weeks of gestation. The secondary outcomes were PTB <37, 32, 28, 24 weeks of gestation, gestational age at birth, the interval between diagnosis and birth, preterm prelabor rupture of the membranes (pPROM), chorioamnionitis, perinatal loss, and perinatal morbidity. Subgroup analyses according to the indication for cerclage (short cervical length or cervical dilatation) were also performed. Risk of bias assessment: The risk of bias of the included randomized controlled trials (RCTs) was assessed using the Revised Cochrane risk-of-bias tool for randomized trials, while that of the observational studies using the Newcastle-Ottawa scale (NOS). Statistical analysis: Summary risk ratios (RRs) of the likelihood of detecting each categorical outcome in exposed versus unexposed women, and (b) summary mean differences (MDs) between exposed and unexposed women (for each continuous outcome), with their 95% confidence intervals (CIs) were computed using head-to-head meta-analyses. Synthesis of the results: Eighteen studies (1,465 twin pregnancies) were included. Placement of cervical cerclage in women with a twin pregnancy with a short cervix at ultrasound or cervical dilatation at physical examination was associated with a reduced risk of PTB <34 weeks of gestation (RR: 0.73, 95% CI [0.59, 0.91], p = 0.005 corresponding to a 16% difference in the absolute risk, AR), <32 (RR: 0.69, 95% CI [0.57, 0.84], p < 0.001; AR: 16.92%), <28 (RR: 0.54, 95% [CI 0.43, 0.67], 0.001; AR: 18.29%), and <24 (RR: 0.48, 95% CI [0.23, 0.97], p = 0.04; AR: 15.57%) weeks of gestation and a prolonged gestational age at birth (MD: 2.32 weeks, 95% [CI 0.99, 3.66], p < 0.001). Cerclage in twin pregnancy with short cervical length or cervical dilatation was also associated with a reduced risk of perinatal loss (RR: 0.38, 95% CI [0.25, 0.60], p < 0.001; AR: 19.62%) and composite adverse outcome (RR: 0.69, 95% CI [0.53, 0.90], p = 0.007; AR: 11.75%). Cervical cerclage was associated with a reduced risk of PTB <34 weeks both in women with cervical length <15 mm (RR: 0.74, 95% CI [0.58, 0.95], p = 0.02; AR: 29.17%) and in those with cervical dilatation (RR: 0.68, 95% CI [0.57, 0.80], p < 0.001; AR: 35.02%). The association between cerclage and prevention of PTB and adverse perinatal outcomes was exclusively due to the inclusion of observational studies. The quality of retrieved evidence at GRADE assessment was low.

CONCLUSIONS

Emergency cerclage for cervical dilation or short cervical length <15 mm may be potentially associated with a reduction in PTB and improved perinatal outcomes. However, these findings are mainly based upon observational studies and require confirmation in large and adequately powered RCTs.

Diagnosis or prognosis? An umbrella review of mid-trimester cervical length and spontaneous preterm birth

BACKGROUND

Cervical length is widely used to assess a woman's risk of spontaneous preterm birth (SPTB).

OBJECTIVES

To summarise and critically appraise the evidence from systematic reviews on the prognostic capacity of transvaginal sonographic cervical length in the second trimester in asymptomatic women with singleton or twin pregnancy.

SEARCH STRATEGY

Searches were performed in Medline, Embase, CINAHL and grey literature from 1 January 1995 to 6 July 2021, including keywords 'cervical length', 'preterm birth', 'obstetric labour, premature', 'review' and others, without language restriction.

SELECTION CRITERIA

We included systematic reviews including women who did not receive treatments to reduce SPTB risk.

DATA COLLECTION AND ANALYSIS

From 2472 articles, 14 systematic reviews were included. Summary statistics were independently extracted by two reviewers, tabulated and analysed descriptively. The ROBIS tool was used to evaluate risk of bias of included systematic reviews.

MAIN RESULTS

Twelve reviews performed meta-analyses: two were reported as systematic reviews of prognostic factor studies, ten used diagnostic test accuracy methodology. Ten systematic reviews were at high or unclear risk of bias. Meta-analyses reported up to 80 combinations of cervical length, gestational age at measurement and definition of preterm birth. Cervical length was consistently associated with SPTB, with a likelihood ratio for a positive test of 1.70-142.

CONCLUSIONS

The ability of cervical length to predict SPTB is a prognostic research question; systematic reviews typically analysed diagnostic test accuracy. Individual participant data meta-analysis using prognostic factor research methods is recommended to better quantify how well transvaginal ultrasonographic cervical length can predict SPTB.

Prevention and Therapy of Preterm Birth. Guideline of the DGGG, OEGGG and SGGG (S2k-Level, AWMF Registry Number 015/025, September 2022) - Part 1 with Recommendations on the Epidemiology, Etiology, Prediction, Primary and Secondary Prevention of Preterm Birth

Aim This revised guideline was coordinated by the German Society for Gynecology and Obstetrics (DGGG), the Austrian Society for Gynecology and Obstetrics (OEGGG) and the Swiss Society for Gynecology and Obstetrics (SGGG). It aims to improve the prediction, prevention, and management of preterm birth, based on evidence from the current literature, the experience of members of the guidelines commission, and the viewpoint of self-help organizations. Methods The members of the contributing professional societies and organizations developed recommendations and statements based on international literature. The recommendations and statements were presented and adopted using a formal process (structured consensus conferences with neutral moderation, written Delphi vote). Recommendations Part 1 of this short version of the guideline presents statements and recommendations on the epidemiology, etiology, prediction, and primary and secondary prevention of preterm birth.

Cervical length screening for predicting preterm birth: A comparative review of guidelines

A cervical length (CL) assessment may predict preterm birth (PTB). This study aimed to analyze and compare the recommendations of guidelines on the role of CL in the prediction of PTB. There is no consensus regarding universal screening of asymptomatic women without a history of prior spontaneous PTB (sPTB), using CL. On the other hand, CL assessment is recommended in cases with a history of sPTB due to the high recurrence rate. Finally, there is discrepancy regarding CL assessment in asymptomatic women with multiple pregnancy. Although far from perfect, CL measurement remains the best available method to predict PTB.

Time interval to delivery in asymptomatic twin pregnancies with a short cervix at 23-28 weeks' gestation

OBJECTIVES

To evaluate the risk and timing of spontaneous preterm birth (PTB) in asymptomatic twin pregnancies with a short cervical length (CL≤25 mm) at 23-28 weeks of gestation.

METHODS

Multicenter retrospective cohort study of asymptomatic twin pregnancies with a short CL between 23 and 28 weeks' gestation within a university health system from 1/2012 to 12/2019. Cases were divided into 4 groups based on CL measurement (≤10 mm, 11-15 mm, 16-20 mm, and 21-25 mm). The primary outcome was time interval from presentation to delivery. Secondary outcomes included delivery within one and two weeks of presentation, and delivery prior to 32, 34, and 37 weeks, respectively.

RESULTS

104 patients were included. The time interval from presentation to delivery was significantly different among the four groups (p<0.001), with the CL≤10 mm group having the shortest time interval to delivery. Regardless of the CL measurement, spontaneous PTB within one and two weeks was extremely uncommon and occurred in only one patient within the study cohort (1/104, 1.0%). The risk of spontaneous PTB was highest in the shortest CL group (CL ≤ 10 mm; 53.8% PTB<32 weeks, 61.5% PTB<34 weeks, 92.3% PTB<37 weeks).

CONCLUSIONS

Asymptomatic twin pregnancies with a CL ≤ 10 mm had the shortest time interval to delivery and thus represent a specifically high risk group for sPTB. Although all patients were at high risk of sPTB, only one delivered within 1 or 2 weeks of presentation.

Gestational age-based reference ranges for cervical length and preterm birth prediction in triplet pregnancies: an observational retrospective study

OBJECTIVES

To develop gestational age-based reference ranges for cervical length in triplet pregnancies. The secondary objective was to assess the performance of cervical length measured between 18 and 20 + 6 days for the prediction of preterm delivery before 28 and 32 weeks, respectively.

METHODS

Observational retrospective study of triplet pregnancies in three Spanish tertiary-care hospitals between 2001 and 2019. Cervical length measurements were consecutively obtained between 15 and 34 weeks of gestation. Pregnancies undergoing multifetal reduction or fetal surgery were excluded.

RESULTS

Two hundred and six triplet pregnancies were included in the final analysis. There was a quadratic decrease in cervical length with gestational age. The median and fifth centiles for cervical length at 20 weeks were 35 and 13 mm. In the prediction of preterm birth < 28 weeks, for a false positive rate of 5%, and 10%, the detection rates were 40.9%, and 40.9%, respectively, and the prediction of preterm birth < 32 weeks, 22.0% and 26.0%, respectively.

CONCLUSIONS

In triplet pregnancies, cervical length decreases with gestational age. The performance of cervical length at 18-20 + 6 in screening for preterm birth before 28 and 32 weeks is poor.

Clinical Value and Treatment Progress of Prenatal Ultrasonography in Twin Pregnancy: A Systematic Review

Assisted reproductive technology has continued to develop in recent years, the technology has become more and more mature, and it has improved the total gestational age of the population. Assisted reproductive technology has improved twin pregnancy rates with the use of ovulation-inducing drugs. The risk factor of twins is much higher than singletons, and adverse pregnancy outcomes such as stillbirth and premature birth are more likely to occur than singletons, especially the special complications of monochorionic twins (MC), and the neonatal mortality and morbidity are also increased. Prenatal diagnosis and prognosis of twin pregnancy, as well as therapeutic interventions, are of current concern. Ultrasound can realize the understanding of intrauterine growth and development of twin pregnancy fetuses during pregnancy, can more accurately determine gestational age, organ function, and maturity, and timely detect fetal growth and development abnormalities in twin pregnancy, while the prognosis and treatment still need further improvement. The purpose of this study was to investigate the clinical value and treatment progress of prenatal ultrasound monitoring in twin pregnancy.

Guideline No. 428: Management of Dichorionic Twin Pregnancies

OBJECTIVE

To review evidence-based recommendations for the management of dichorionic twin pregnancies.

TARGET POPULATION

Pregnant women with a dichorionic twin pregnancy.

BENEFITS, HARMS, AND COSTS

Implementation of the recommendations in this guideline may improve the management of twin pregnancies and reduce neonatal and maternal morbidity and mortality.

EVIDENCE

Published literature was retrieved through searches of PubMed and the Cochrane Library using appropriate controlled vocabulary (e.g., twin, preterm birth). Results were restricted to systematic reviews, randomized controlled trials, controlled clinical trials, and observational studies. There were no date limits, but results were limited to English- or French-language materials.

VALIDATION METHODS

The content and recommendations were drafted and agreed upon by the principal authors. The Board of the SOGC approved the final draft for publication. The authors rated the quality of evidence and strength of recommendations using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach. See online Appendix A (Tables A1 for definitions and A2 for interpretations of strong and weak recommendations).

INTENDED AUDIENCE

Obstetricians, family physicians, nurses, midwives, maternal-fetal medicine specialists, radiologists, and other health care providers who care for women with twin pregnancies.

SUMMARY STATEMENTS

RECOMMENDATIONS.

Preterm Labor: A Comprehensive Review of Guidelines on Diagnosis, Management, Prediction and Prevention

Importance

Preterm labor (PTL) is one of the most common and serious pregnancy complications associated with significant perinatal morbidity and mortality, as well as long-term neurologic impairment in the offspring.

Objective

The aim of this study was to review and compare the most recently published major guidelines on diagnosis, management, prediction, and prevention of this severe complication of pregnancy.

Evidence Acquisition

A descriptive review of guidelines from the National Institute for Health and Care Excellence (NICE), the World Health Organization, the American College of Obstetricians and Gynecologists, the New South Wales Government, and the European Association of Perinatal Medicine (EAPM) on PTL was carried out.

Results

There is a consensus among the reviewed guidelines that the diagnosis of PTL is based on clinical criteria, physical examination, measurement of cervical length (CL) with transvaginal ultrasound (TVUS) and use of biomarkers, although there is disagreement on the first-line diagnostic test. The NICE and the EAPM are in favor of TVUS CL measurement, whereas the New South Wales Government mentions that fetal fibronectin testing is the mainstay for PTL diagnosis. Moreover, there is consistency among the guidelines regarding the importance of treating PTL up to 34 weeks of gestation, to delay delivery for 48 hours, for the administration of antenatal corticosteroids, magnesium sulfate, and in utero transfer to higher care facility, although several discrepancies exist regarding the tocolytic drugs of choice and the administration of corticosteroids and magnesium sulfate after 34 and 30 gestational weeks, respectively. Routine cesarean delivery in case of PTL is unanimously not recommended. Finally, the NICE, the American College of Obstetricians and Gynecologists, and the EAPM highlight the significance of screening for PTL by TVUS CL measurement between 16 and 24 weeks of gestation and suggest the use of either vaginal progesterone or cervical cerclage for the prevention of PTL, based on specific indications. Cervical pessary is not recommended as a preventive measure.

Conclusions

Preterm labor is a significant contributor of perinatal morbidity and mortality with a substantial impact on health care systems. Thus, it seems of paramount importance to develop consistent international practice protocols for timely diagnosis and effective management of this major obstetric complication and subsequently improve pregnancy outcomes.

Study protocol to quantify the genetic architecture of sonographic cervical length and its relationship to spontaneous preterm birth

INTRODUCTION

A short cervix (cervical length <25 mm) in the midtrimester (18-24 weeks) of pregnancy is a powerful predictor of spontaneous preterm delivery. Although the biological mechanisms of cervical change during pregnancy have been the subject of extensive investigation, little is known about whether genes influence the length of the cervix, or the extent to which genetic factors contribute to premature cervical shortening. Defining the genetic architecture of cervical length is foundational to understanding the aetiology of a short cervix and its contribution to an increased risk of spontaneous preterm delivery.

METHODS/ANALYSIS

The proposed study is designed to characterise the genetic architecture of cervical length and its genetic relationship to gestational age at delivery in a large cohort of Black/African American women, who are at an increased risk of developing a short cervix and delivering preterm. Repeated measurements of cervical length will be modelled as a longitudinal growth curve, with parameters estimating the initial length of the cervix at the beginning of pregnancy, and its rate of change over time. Genome-wide complex trait analysis methods will be used to estimate the heritability of cervical length growth parameters and their bivariate genetic correlation with gestational age at delivery. Polygenic risk profiling will assess maternal genetic risk for developing a short cervix and subsequently delivering preterm and evaluate the role of cervical length in mediating the relationship between maternal genetic variation and gestational age at delivery.

ETHICS/DISSEMINATION

The proposed analyses will be conducted using deidentified data from participants in an IRB-approved study of longitudinal cervical length who provided blood samples and written informed consent for their use in future genetic research. These analyses are preregistered with the Center for Open Science using the AsPredicted format and the results and genomic summary statistics will be published in a peer-reviewed journal.

Pregnancy Loss After Amniocentesis with Double-Needle Insertions in Twin Pregnancies

The aim of this study was to determine the pregnancy loss rate of amniocentesis with double-needle insertions in twin pregnancies. This was a retrospective study of twin pregnancies who underwent amniocentesis with double-needle insertion between 2010 and 2019 at a single center. The pregnancy loss rates were recorded as single or double fetal loss before 24 weeks’ gestation and within 4 weeks after the procedure. Risk factors for pregnancy loss after amniocentesis were also assessed. A total of 678 twin pregnancies with amniocentesis were finally included. The pregnancy loss rates before 24 weeks’ gestation and within 4 weeks after the procedure were 0.9% and 1.9%, respectively. Only one fetal loss was presumed to be a direct result of the procedure. All other cases were complicated by structural or chromosomal anomalies. Twin pregnancies with abnormal ultrasound findings had a significantly higher rate of pregnancy loss with a relative risk of 4.81 (95% CI [1.03, 22.2]). Our study showed a low pregnancy loss rate after amniocentesis in twin pregnancies with double-needle insertions technique of sampling, which can help decision making in prenatal screening and diagnosis for twin pregnancies.

Prediction and Prevention of Spontaneous Preterm Birth: ACOG Practice Bulletin, Number 234

Preterm birth is among the most complex and important challenges in obstetrics. Despite decades of research and clinical advancement, approximately 1 in 10 newborns in the United States is born prematurely. These newborns account for approximately three-quarters of perinatal mortality and more than one half of long-term neonatal morbidity, at significant social and economic cost (1-3). Because preterm birth is the common endpoint for multiple pathophysiologic processes, detailed classification schemes for preterm birth phenotype and etiology have been proposed (4, 5). In general, approximately one half of preterm births follow spontaneous preterm labor, about a quarter follow preterm prelabor rupture of membranes (PPROM), and the remaining quarter of preterm births are intentional, medically indicated by maternal or fetal complications. There are pronounced racial disparities in the preterm birth rate in the United States. The purpose of this document is to describe the risk factors, screening methods, and treatments for preventing spontaneous preterm birth, and to review the evidence supporting their roles in clinical practice. This Practice Bulletin has been updated to include information on increasing rates of preterm birth in the United States, disparities in preterm birth rates, and approaches to screening and prevention strategies for patients at risk for spontaneous preterm birth.

Screening, Management and Delivery in Twin Pregnancy

The following AWMF guideline (DGGG/AGG & DEGUM responsible) deals with the diagnosis, screening and management of twins as well as the timing and mode of birth.Twin pregnancies can be classified as dichorionic diamniotic (DC DA), monochorionic diamniotic (MC DA) and monochorionic monoamniotic (MC MA) which are always monochorionic.Twin pregnancies can be concordant (both twins are affected) or discordant (only one twin is affected) for chromosomal defects, malformations, growth restriction and hemodynamic disorders.Chorionicity is the prognostically most significant parameter. Monochorial twins have significantly higher risks of intrauterine morbidity and mortality compared to dichorial twins.In particular, general aspects of twin pregnancies such as dating, determination of chorionicity and amnionicity, the labeling of twin fetuses and the perinatal switch phenomenon are discussed.Routine monitoring of MC and DC twin pregnancies with ultrasound at 11-13^+ 6 weeks of gestation for chromosomal defects, invasive prenatal diagnosis, first-trimester NT or CRL discrepancies, early diagnosis of fetal anatomical defects, and management of twins with abnormalities, including selective fetocide, is described.Second trimester screening and management for preterm birth, intrauterine selective growth restriction (sFGR), classification of monochorial twins with sFGR, and management of the surviving twin after the death of the co-twin are described.Complications exclusively affecting MC twins include Twin to Twin Transfusion Syndrome (TTTS) with the important topics screening, prognosis, complications of laser therapy, timing of delivery, risks for brain abnormalities and delayed neurological development, Twin Anemia-Polycythemia Sequence (TAPS) and Twin Reversed Arterial Perfusion (TRAP) Sequence. This also includes MC MA twins as well as conjoined twins.Finally, the birth mode and time for DC and MC twin pregnancies are described.The information is summarized in 62 recommendations for action, 4 tables and 8 illustrations with comprehensive background texts.The guideline is an international guideline adaptation (ISUOG, NICE) as well as a systematic literature search and is up-to-date.

Self-reported pain scores as a predictor of preterm birth in symptomatic twin pregnancy: a retrospective study

BACKGROUND

To evaluate the self-reported pain scores as a predictor of preterm birth (PTB) in symptomatic twin pregnancy and to develop a nomogram for the prediction model.

METHODS

We conducted a retrospective study of 148 cases of symptomatic twin pregnancies before 34 weeks of gestation visited at Seoul national university hospital from 2013 to 2018. With other clinical factors, self-reported pain score was evaluated by the numerical rating scale (NRS) pain scores for pain intensity. By multivariate analyses and logistic regression, we developed a prediction model for PTB within 7 days. Using the Cox proportional hazards model, the curves were plotted to show the predictability of the PTB according to NRS pain score, while adjusting the other covariates.

RESULTS

Twenty-three patients (15.5 %) delivered preterm within 7 days. By a logistic regression analysis, higher NRS pain score (OR 1.558, 95 % CI 1.093-2.221, P < 0.05), shorter cervical length (OR 3.164, 95 % CI 1.262-7.936, P < 0.05) and positive fibronectin results (OR 8.799, 95 % CI 1.101-70.330, P < 0.05) affect PTB within 7 days. Using the variables, the area under the receiver operating characteristic curve (AUROC) of the prediction model was 0.917. In addition, we developed a nomogram for the prediction of PTB within 7 days.

CONCLUSIONS

Self-reported pain scores combined with cervical length and fetal fibronectin are useful in predicting impending PTB in symptomatic twin pregnancy.

Controversies in the management of twin pregnancy

Despite many advances in antenatal care, twin pregnancies still experience more adverse outcomes, in particular perinatal morbidity and mortality. They also pose a multitude of challenges and controversies, as outlined in this Review. Moreover, they are less likely to be included in clinical trials. Many issues on classification and management remain under debate. Efforts at standardizing diagnostic criteria, monitoring protocols, management and outcome reporting are likely to reduce their perinatal risks. The top 10 most important research uncertainties related to multiple pregnancies have been identified by both clinicians and patients. More robust research in the form of randomized trials and large well-conducted prospective cohort studies is needed to address these controversies. © 2020 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

Intrapartum stillbirth for sepsis complicating Arabin cervical pessary placement in a twin pregnancy

There is little evidence regarding the best treatment in case of dilated cervix and exposed membranes in twins. Current options for its management include vaginal progesterone, cervical cerclage and cervical pessary, but none of them had shown effectiveness compared to expectant management. We presented a case of twin pregnancy at 22 6/7 weeks' gestation admitted to the hospital because of cervical insufficiency with bulging of membranes. An Arabin pessary was positioned after a failed attempt of cervical cerclage and no antibiotic was given in absence of signs of infection. Cesarean delivery was performed at 24 weeks' gestation because of spontaneous preterm labor and spontaneous rupture of membranes with the first baby in a transverse lie position. At the uterus section, the first baby was stillborn, with Arabin pessary strictly adherent to his ecchymotic head, while the second baby was born alive. After diagnostic histopathological and microbiological investigations, we hypothesized that the first twin died for funisitis/sepsis and mechanical insult due to the strict adhesion of the pessary to the fetal head. We concluded that in case of bulging membranes and dilated cervix, antibiotic treatment should be evaluated, also in absence of signs/symptoms of infection or suspicion of rupture of the membranes, and pessary insertion should be avoided, namely at second trimester, because of the risk of its dislocation inside the uterus when contractions start and potential hurt to extremely preterm fetus.

Outcomes of ultrasound-indicated cerclage in twin pregnancies with a short cervical length

OBJECTIVE

To investigate the outcomes of ultrasound-indicated cerclage in dichorionic-diamniotic (DCDA) twin pregnancies with a short cervical length.

MATERIALS AND METHODS

This was a retrospective cohort study of DCDA twin pregnancies with a short cervical length (≤25 mm) from January 2000 to July 2017 to compare maternal and neonatal outcomes. Additional sub-analysis was performed by dividing the patients into two subgroups by a cervical length ≤15 mm and between 16 and 25 mm.

RESULTS

One hundred and eight women were initially diagnosed with twin pregnancies and cervical insufficiency. After excluding cases not meeting the study criteria, 46 women were recruited for analysis, of whom 33 underwent ultrasound-indicated cerclage. The delivery age of the cerclage group was significantly later than the non-cerclage group (34.85 ± 3.91 versus 31.08 ± 5.25 weeks, p = 0.011), and the latency was significantly longer in the cerclage group than in the non-cerclage group (86.09 ± 41.32 versus 52.31 ± 33.24 days, p = 0.014). Sub-analysis revealed that these benefits were significant in the subgroup of a cervical length ≤15 mm. Both first twin (twin A) and second twin (twin B) had a significantly decreased rate of neonatal intensive care unit admission in the cerclage group. However, twin A had more promising outcomes with significantly decreased rates of neonatal respiratory distress syndrome (6.7% versus 50.0%, p = 0.004) and sepsis (0% versus 25.0%, p = 0.019).

CONCLUSION

Ultrasound-indicated cerclage in DCDA twin pregnancies can decrease preterm birth and prolong the latency. It also decreases neonatal morbidity, and is especially beneficial for twin A.

Management of Twin Pregnancies: A Comparative Review of National and International Guidelines

Importance

Twin pregnancies are associated with a higher risk of perinatal mortality and morbidity compared with singleton and require more intensive prenatal care.

Objective

The aim of this study was to review and compare the recommendations from published guidelines on twin pregnancies.

Evidence Acquisition

A descriptive review of guidelines from the Royal College of Obstetricians and Gynaecologists, the International Society of Ultrasound in Obstetrics and Gynecology, the Royal Australian and New Zealand College of Obstetricians and Gynaecologists, the National Institute for Health and Care Excellence, the Institute of Obstetricians and Gynaecologists of the Royal College of Physicians of Ireland, the International Federation of Gynecology and Obstetrics, the Society of Obstetricians and Gynaecologists of Canada, and the American College of Obstetricians and Gynecologists on the management of twin pregnancies was conducted.

Results

All the guidelines highlight the importance of an accurate assessment of chorionicity, amnionicity, and gestational age in the first trimester. They also recommend the performance of nuchal translucency and a detailed anomaly scan. The ultrasound surveillance protocol is similar in all guidelines, that is, every 2 weeks for monochorionic and every 4 weeks for dichorionic twins. On the other hand, there are differences regarding the timing and mode of delivery, especially in monochorionic diamniotic twins, in the definition and management of fetal growth discordance, the use of cervical length to screen for preterm birth, and the timing of corticosteroids' administration.

Conclusions

The differences in the reviewed guidelines on the management of twin pregnancies highlight the need for an adoption of an international consensus, in order to improve perinatal outcomes of twin pregnancies.

Uterocervical angle at 20 weeks: A promising predictor of spontaneous preterm birth in twin pregnancies

OBJECTIVE

To compare the performance of uterocervical angle (UCA) and cervical length (CL) measurement at 20 weeks of pregnancy for prediction of spontaneous preterm birth (sPTB) in twin pregnancies.

STUDY DESIGN

We conducted a retrospective cohort study of 424 twin pregnancies who delivered in our center from October 2014 to December 2018 and who underwent transvaginal ultrasound between 19⁺⁰-22⁺⁰ weeks to measure CL during routine second trimester scan. Recorded ultrasound images of CL were reassessed to evaluate UCA. Medical and obstetric data were also collected for statistical analysis.

RESULTS

A total of 424 women were included. The rates of sPTB rate below 28, 32 and 34 weeks of gestation were 2.8 %, 5.4 % and 10.4 %, respectively. ROC curves showed a better area under the curve (AUC) for UCA at all gestational ages compared with CL (AUC for sPTB <28 weeks 0.902 (p < 0.001) vs 0.620 (p 0.175); AUC for sPTB <32 weeks 0.740 (p 0.001) vs 0.620 (p 0.058); AUC for sPTB <34 weeks 0.676 (p 0.001) vs 0.632 (p 0.047). UCA > 120 degrees was significantly associated with sPTB <28 weeks (p < 0.001; OR 39.17; CI 4.81-319.23; NPV, 99.65 %), <32 weeks (OR 4.23; p 0.002) and <34 weeks of gestation (OR 2.66; p 0.01).

CONCLUSION

In our study, an UCA > 120 degrees allowed to identify those women with twin pregnancies at risk of sPTB and performed better than CL measurement.

Cervical Assessment for Predicting Preterm Birth-Cervical Length and Beyond

Preterm birth is considered one of the main etiologies of neonatal death, as well as short- and long-term disability worldwide. A number of pathophysiological processes take place in the final unifying factor of cervical modifications that leads to preterm birth. In women at high risk for preterm birth, cervical assessment is commonly used for prediction and further risk stratification. This review outlines the rationale for cervical length screening for preterm birth prediction in different clinical settings within existing and evolving new technologies to assess cervical remodeling.

Prediction of Preterm Delivery by Ultrasound Measurement of Cervical Length and Funneling Changes of the Cervix in Pregnant Women with Preterm Labor at 28-34 weeks of Gestation

The present study aims at predicting preterm delivery by ultrasound measurement of cervical length and the funneling changes of the cervix in preterm labor pregnant women at 28-34 weeks of gestation. The present study is an observational-analytical study with a prospective cohort design. The statistical population of this study includes 70 preterm labor pregnant women who were referred to Tehran hospitals from March 2018 to March 2020. The case group includes 35 women who had short cervical length as well as the funneling changes of the cervix. The control group includes 35 patients whose cervical length was normal and lacked the funneling changes of the cervix. The samples were analyzed after being collected. The mean age of mothers was 29.22 years in the short cervical length group (SD=4.64) and 28.45 years in the normal cervical length group (SD=4.59). The mean length of cervical length was 17.34 mm in the short cervical length group (SD=5.64) and 38.74 mm in the normal cervical length group (SD=4.53). In the case group, the delivery occurred two or seven days after the first visit; as for the proper cervical length group without funneling changes, the delivery occurred 14 days after the first delivery. Thus, the difference is statistically significant (P=0.00). In terms of the preterm delivery before week 34, there was also a significant difference between the short and normal cervical length group, as well as the groups with the funnel-shaped and non-funnel-shaped cervix (P=0.00). However, in terms of post-term delivery before week 37, there was no significant difference between short and normal cervical length groups as well as funneled and non-funneled groups (P=0.78). In terms of term labor, there was a significant difference between short and normal cervical length groups, as well as funneled and non-funneled groups (P=0.00). In investigating the cut-off point with good sensitivity, it was indicated that the cervical length and cervical funneling in pregnant women at risk predict preterm labor before week 34. With the measurement of cervical length and diagnosis of cervical funneling by applying ultrasound, preterm delivery before week 34 can be predicted. Therefore, neonatal mortality and morbidity rates can be reduced in this way.

Does late second-trimester cervical length predict unscheduled preterm birth in asymptomatic triplet pregnancies?

OBJECTIVE

Multiple gestation increases the risk of unscheduled preterm birth (PTB), both spontaneous and indicated, leading to increased neonatal morbidity and additional healthcare costs. The purpose of this study was to determine whether cervical length (CL) assessment by 28 weeks could predict unscheduled PTB <34 weeks in triplet pregnancies. Secondary outcomes included prediction of PTB <30 weeks, prediction of PTB based on degree of cervical change and effect of ART-use on PTB.

METHODS

This was a retrospective cohort of women with triplet pregnancies. The exposure variable of interest was short cervix < 25 and <20 millimeters (mm) by 28 weeks. Maternal characteristics were described. The distribution of CLs was analyzed by the primary outcome of unscheduled PTB < 34 weeks, and by PTB <30 weeks (secondary outcome). Gestational age at delivery was compared between women with and without a short cervix. Changes in CL were compared between the groups with unscheduled PTB and those delivering ≥34 and ≥30 weeks. Statistical analyses were performed using appropriate tests.

RESULTS

Of 92 triplet pregnancies, 51 met the criteria, with 1233 total (411 shortest) CL measurements from 16 to 34 weeks' gestation. The overall rate of PTB <34 weeks was 31.4% and <30 weeks was 9.8%. The median gestational age at delivery was 32.7 (IQR 2.3) weeks. There were no statistically significant differences in rates of unscheduled PTB in women who had a short cervix and those that did not: PTB <34 weeks with CL <25 mm (p = .53) and CL <20 mm (p = .70); PTB <30 weeks with CL <25 mm (p = .38) and CL <20 mm (p = .26). The degree of cervical change from 18 to 28 weeks was not statistically significant for predicting unscheduled PTB <34 and <30 weeks. Of 70.6% of triplet pregnancies conceived by ARTs, 13.9% had unscheduled PTB <30 weeks, whereas no spontaneously-conceived pregnancies delivered <30 weeks (p = .14).

CONCLUSION

Short cervix did not predict unscheduled spontaneous PTB <34 weeks nor <30 weeks in our triplet cohort, nor did the degree of cervical change by 28 weeks predict PTB. Triplets conceived by ARTs may have an increased risk of unscheduled PTB.

Cervical Pessary Plus Progesterone for Twin Pregnancy with Short Cervix Compared to Unselected and Non-Treated Twin Pregnancy: A Historical Equivalence Cohort Study (EPM Twin Pessary Study)

OBJECTIVE

 The present study aims to determine if the use of cervical pessary plus progesterone in short-cervix (≤ 25 mm) dichorionic-diamniotic (DC-DA) twin pregnancies is equivalent to the rate of preterm births (PBs) with no intervention in unselected DC-DA twin pregnancies.

METHODS

 A historical cohort study was performed between 2010 and 2018, including a total of 57 pregnant women with DC-DA twin pregnancies. The women admitted from 2010 to 2012 (n = 32) received no treatment, and were not selected by cervical length (Non-Treated group, NTG), whereas those admitted from 2013 to 2018 (n = 25), were routinely submitted to cervical pessary plus progesterone after the diagnosis of short cervix from the 18th to the 27th weeks of gestation (Pessary-Progesterone group, PPG). The primary outcome analyzed was the rate of PBs before 34 weeks.

RESULTS

 There were no statistical differences between the NTG and the PPG regarding PB < 34 weeks (18.8% versus 40.0% respectively; p = 0.07) and the mean birthweight of the smallest twin (2,037 ± 425 g versus 2,195 ± 665 g; p = 0.327). The Kaplan-Meyer Survival analysis was performed, and there were no differences between the groups before 31.5 weeks. Logistic regression showed that a previous PB (< 37 weeks) presented an odds ratio (OR) of 15.951 (95% confidence interval [95%CI]: 1.294-196.557; p = 0.031*) for PB < 34 weeks in the PPG.

CONCLUSION

 In DC-DA twin pregnancies with a short cervix, (which means a higher risk of PB), the treatment with cervical pessary plus progesterone could be considered equivalent in several aspects related to PB in the NTG, despite the big difference between these groups.

Association between chorionicity and preterm birth in twin pregnancies: a systematic review involving 29 864 twin pregnancies

BACKGROUND

The perinatal mortality and morbidity among twins vary by chorionicity. Although it is considered that monochorionicity is associated with an increased risk of preterm birth in twin pregnancies, no systematic review exists evaluating this association.

OBJECTIVES

This systematic review was undertaken to assess the association between preterm birth and chorionicity in twin pregnancies.

SEARCH STRATEGY

We searched the electronic databases from January 1990 to July 2019 without language restrictions.

SELECTION CRITERIA

All studies on twin pregnancies where chorionicity and preterm birth were evaluated were included.

DATA COLLECTION AND ANALYSIS

Findings are reported as odds ratios with 95% confidence intervals. The estimates are pooled using random-effects meta-analysis.

MAIN RESULTS

From 13 156 citations, we included 39 studies (29 864 pregnancies). Monochorionicity was significantly associated with increased risk of preterm birth at ≤28, ≤32, ≤34 and <37 weeks in women asymptomatic and symptomatic for preterm labour (odds ratio [OR] 2.14, 95% CI 1.52-3.02, I²  = 46%, OR 1.55, 95% CI 1.27-1.89 I²  = 68%, OR 1.47, 95% CI 1.27-1.69, I²  = 60%, OR 1.66, 95% CI 1.43-1.93, I²  = 65%, respectively). Among those asymptomatic for preterm labour, significantly increased odds of preterm birth were seen for monochorionicity at gestations ≤34 weeks (OR 1.85, 95% CI 1.42-2.40, I²  = 25%) and <37 weeks (OR 1.75, 95% CI 1.22-2.53, I²  = 61%). Sensitivity analysis showed significantly increased odds of spontaneous preterm birth at ≤34 and <37 weeks for monochorionicity (OR 1.25, 95% CI 1.01-1.55, I²  = 0% and OR 1.41, 95% CI 1.13-1.78, I²  = 0%).

CONCLUSIONS

Monochorionicity is significantly associated with preterm birth at all gestations.

TWEETABLE ABSTRACT

In twin pregnancies, monochorionicity is associated with an increased risk of preterm birth at all gestations.