1.Carvedilol to prevent hepatic decompensation of cirrhosis in patients with clinically significant portal hypertension stratified by new non-invasive model (CHESS2306)
Chuan LIU ; Hong YOU ; Qing-Lei ZENG ; Yu Jun WONG ; Bingqiong WANG ; Ivica GRGUREVIC ; Chenghai LIU ; Hyung Joon YIM ; Wei GOU ; Bingtian DONG ; Shenghong JU ; Yanan GUO ; Qian YU ; Masashi HIROOKA ; Hirayuki ENOMOTO ; Amr Shaaban HANAFY ; Zhujun CAO ; Xiemin DONG ; Jing LV ; Tae Hyung KIM ; Yohei KOIZUMI ; Yoichi HIASA ; Takashi NISHIMURA ; Hiroko IIJIMA ; Chuanjun XU ; Erhei DAI ; Xiaoling LAN ; Changxiang LAI ; Shirong LIU ; Fang WANG ; Ying GUO ; Jiaojian LV ; Liting ZHANG ; Yuqing WANG ; Qing XIE ; Chuxiao SHAO ; Zhensheng LIU ; Federico RAVAIOLI ; Antonio COLECCHIA ; Jie LI ; Gao-Jun TENG ; Xiaolong QI
Clinical and Molecular Hepatology 2025;31(1):105-118
Background:
s/Aims: Non-invasive models stratifying clinically significant portal hypertension (CSPH) are limited. Herein, we developed a new non-invasive model for predicting CSPH in patients with compensated cirrhosis and investigated whether carvedilol can prevent hepatic decompensation in patients with high-risk CSPH stratified using the new model.
Methods:
Non-invasive risk factors of CSPH were identified via systematic review and meta-analysis of studies involving patients with hepatic venous pressure gradient (HVPG). A new non-invasive model was validated for various performance aspects in three cohorts, i.e., a multicenter HVPG cohort, a follow-up cohort, and a carvediloltreating cohort.
Results:
In the meta-analysis with six studies (n=819), liver stiffness measurement and platelet count were identified as independent risk factors for CSPH and were used to develop the new “CSPH risk” model. In the HVPG cohort (n=151), the new model accurately predicted CSPH with cutoff values of 0 and –0.68 for ruling in and out CSPH, respectively. In the follow-up cohort (n=1,102), the cumulative incidences of decompensation events significantly differed using the cutoff values of <–0.68 (low-risk), –0.68 to 0 (medium-risk), and >0 (high-risk). In the carvediloltreated cohort, patients with high-risk CSPH treated with carvedilol (n=81) had lower rates of decompensation events than non-selective beta-blockers untreated patients with high-risk CSPH (n=613 before propensity score matching [PSM], n=162 after PSM).
Conclusions
Treatment with carvedilol significantly reduces the risk of hepatic decompensation in patients with high-risk CSPH stratified by the new model.
2.Identification of Taste Critical Quality Attribute and Formulation Optimization of Qingre Jiedu Oral Liquid Based on the Combination of Electronic Tongue and Real Human Senses
Xingyue HUAN ; Zhisheng WU ; Ying LU ; Haiyang LI ; Shuoshuo XU ; Han HE ; Qiatong XIE ; Nan LI ; Jun JIA ; Lu YAO ; Run ZHANG ; Jiafu CHEN ; Xingxing DAI
World Science and Technology-Modernization of Traditional Chinese Medicine 2025;27(11):3213-3223
Objective To identify the taste critical quality attribute and design and optimize the flavor-correcting formulation of the traditional Chinese medicine oral preparation Qingre Jiedu Oral Liquid,in order to improve its taste and enhance patient medication adherence.Methods The taste assignment method was employed to identify the taste critical quality attribute of Qingre Jiedu Oral Liquid.Based on human sensory evaluation and the standardized Euclidean distance in electronic tongue analysis,suitable types of corrigent were determined.Subsequently,under constraints such as maximum allowable dosage,solubility,and sweetness,the optimal taste formulation for the sugar-free intermediate of Qingre Jiedu Oral Liquid was determined using Box-Behnken experimental design combined with electronic tongue and human sensory evaluation results.The study was reviewed and approved by the Ethics Committee of Beijing University of Chinese Medicine(Ethics Approval Number 2020BZYLL0609).Results The quantitative score for bitter taste of Qingre Jiedu Oral Liquid accounted for 30.36%,confirming bitterness as the taste critical quality attribute requiring attention.The optimal taste formulation for the sugar-free intermediate of Qingre Jiedu Oral Liquid was determined to be 120 mg·mL?1 erythritol,12 mg·mL?1 acesulfame potassium,and 2.4 mg·mL?1 stevioside.This formulation achieved an 11.75-point improvement in sensory evaluation scores compared to the original commercially available oral liquid.Conclusion This study successfully improved the taste of Qingre Jiedu Oral Liquid and established a comprehensive strategy for flavor-correcting formulation optimization,including a method for identifying taste critical quality attribute.This strategy provides a referential paradigm for palatability enhancement of similar traditional Chinese medicine oral preparations,laying a crucial technical foundation for elevating the clinical value of Chinese herbal medicines and promoting the high-quality development of traditional Chinese medicine(TCM).
3.Cross-sectional survey of healthcare-associated infection in 5 736 medical institutions across China in 2024
Cui ZENG ; Wuqiang GAO ; Fu QIAO ; Hui ZHAO ; Xu FANG ; Linping LI ; Xiuwen CHEN ; Jiansen CHEN ; Dan LI ; Yuan ZHOU ; Lingli YU ; Qinglan MENG ; Xia MOU ; Lijuan XIONG ; Weiguang LI ; Ding LIU ; Jiaqing XIAO ; Limei OU ; Baozhen LI ; Jun YIN ; Haojun ZHANG ; Qiang FU ; Qun LU ; Biao WU ; Ya-wei XING ; Shumei SUN ; Shuncai WANG ; Longmin DU ; Jingping ZHANG ; Wen-ying HE ; Gui CHENG ; Nan REN ; Xun HUANG ; Anhua WU
Chinese Journal of Infection Control 2025;24(11):1572-1583
Objective To understand the current situation of healthcare-associated infection(HAI)in China,pro-vide data support and decision-making basis for formulating scientific and effective strategies for HAI prevention and control.Methods A nationwide cross-sectional survey on HAI was conducted among various types and levels of medical institutions in China according to a unified protocol of bedside surveys and case investigations.Results In 2024,a total of 5 736 medical institutions and 2 751 765 patients were surveyed.Among them,34 889 HAI cases were identified,with a prevalence rate of 1.27%.The number of HAI episodes was 38 032,and case prevalence rate was 1.38%.The prevalence rate of HAI in medical institutions in different regions of China ranged from 0.66%to 2.35%.Among medical institutions of different scales,those with a bed capacity of ≥900 had the high-est incidence of HAI,reaching 1.65%.The most common infection site was the lower respiratory tract(44.66%),followed by the urinary tract(12.94%),surgical site(9.32%),upper respiratory tract(7.02%),and bloodstream infection(5.78%).The top 3 departments with the highest HAI rates were the general intensive care unit(10.02%),department of neurosurgery(5.51%),and department(group)of hematology(5.34%).A total of 23 238 strains of HAI pathogens were detected,with 10 714 strains(46.10%)from lower respiratory tract speci-mens.The top 5 detected strains were Klebsiella pneumoniae(14.76%),Pseudomonas aeruginosa(13.33%),Escherichia coli(12.79%),Acinetobacter baumannii(9.23%),and Staphylococcus aureus(7.88%).231 944 pa-tients underwent class Ⅰ incision surgery were monitored,with 1 647 cases experienced surgical site infection,and the prevalence rate of surgical site infection was 0.71%.The number of patients who should undergo pathogen de-tection(patients receiving therapeutic and therapeutic combined prophylactic antimicrobial agents)was 715 179,while the actual number was 480 492,with a pathogen detection rate of 67.18%.425 225 patients received patho-genic detection before treatment,with a detection rate of 59.46%.Conclusion The overall HAI prevalence in Chi-na is lower,showing disparities among medical institutions of different regions and scales.Therefore,precise imple-mentation of measures is necessary for HAI prevention and control,with a focus on high-risk institutions and high-risk departments,key areas,and critical procedures.All levels of medical institutions should continuously reduce the incidence of HAI by strengthening monitoring,standardizing the use of antimicrobial agents,and reinforcing basic HAI prevention and control measures.
4.A prospective study of the effect of physical activity on mortality risk in patients with chronic obstructive pulmonary disease in Sichuan Province
Ying ZHANG ; Xiaofang CHEN ; Xiaofang CHEN ; Xia WU ; Xiaoyu CHANG ; Zhuo WANG ; Xu HAN ; Jun LYU ; Canqing YU ; Pei PEI ; Dianjianyi SUN ; Xianping WU
Chinese Journal of Epidemiology 2025;46(8):1347-1353
Objective:To investigate the effect of physical activity on mortality risk in patients with chronic obstructive pulmonary disease (COPD) in Sichuan Province.Methods:Based on baseline data from 2004 to 2008 from the China Kadoorie Biobank project site in Pengzhou City, Sichuan Province, a total of 8 501 COPD patients aged 30-79 years were enrolled and followed up for a long period to determine mortality outcomes. Quartiles were used to group physical activity levels. The Cox proportional hazards regression model was used to analyze the effect of physical activity level on mortality outcomes.Results:As of December 31, 2017, the cumulative follow-up of the participants totaled 85 600.58 person-years (mean follow-up duration: 10.07 years). During this period, a total of 2 000 deaths were recorded, yielding a cumulative mortality rate of 23.53%. Among these deaths, 665 were attributed to COPD, corresponding to a cumulative mortality rate of 7.82%; and 1 116 were attributed to cardiovascular and cerebrovascular disease (CVD), corresponding to a cumulative mortality rate of 13.13%. The Cox proportional hazards regression model analysis revealed that, after adjusting for confounding factors, total physical activity was associated with a reduced risk of mortality from COPD, CVD, and all causes in patients with COPD. Compared with the low-level group of total physical activity, the medium-high-level group had the lowest risk of COPD mortality, with an HR of 0.39 (95% CI: 0.30-0.49). The high-level group had the lowest risk of CVD death and all-cause death, with HRs of 0.46 (95% CI: 0.37-0.56) and 0.55 (95% CI: 0.48-0.64), respectively. The lowest risk of COPD death and CVD death was found in the medium-high level of work-based physical activity group, with HRs of 0.36 (95% CI: 0.28-0.46) and 0.43 (95% CI: 0.36-0.51), respectively; the risk of all-cause mortality was lowest in the medium-high and high-level groups, with HRs values of 0.53 (95% CI: 0.46-0.61) and 0.53 (95% CI: 0.45-0.61). The risk of COPD death was lowest in the high-level transportation physical activity group, with an HR of 0.66 (95% CI: 0.53-0.83), and the risk of CVD and all-cause death was lowest in the medium-high level group, with HRs of 0.63 (95% CI: 0.53-0.76) and 0.73 (95% CI: 0.64-0.84), respectively. The risk of COPD death and CVD death was the lowest in the high-level domestic physical activity group, with HRs of 0.66 (95% CI: 0.49-0.89) and 0.76 (95% CI: 0.61-0.95), respectively, and the risk of all-cause death was the lowest in the medium-high level group, with an HR of 0.82 (95% CI: 0.72-0.94). There is no statistical association between leisure physical activity and the risk of death from three types of diseases. Conclusions:Total physical activity, including work-based, transportation-based, and domestic physical activity, reduced the risk of COPD, CVD, and all-cause mortality in patients with COPD in Sichuan Province. The magnitude of mortality risk was influenced by the type and level of physical activity.
5.Correlation between remnant cholesterol/high-density lipoprotein cholesterol ratio and morbidity risk of metabolic dysfunction-associated fatty liver disease in health check-up population
Jun YANG ; Ying LI ; Yanqing WU ; Rong ZENG ; Shiqi TANG ; Lijuan XU ; Ren LIN
Chinese Journal of Health Management 2025;19(8):625-630
Objective:To investigate the correlation between remnant cholesterol/high-density lipoprotein cholesterol ratio (RC/HDL-C) and metabolic dysfunction-associated fatty liver disease (MAFLD) in health check-up population.Methods:It was a cross-sectional study. A total of 5 299 subjects who received physical examination in the Health Management Center of Renmin Hospital of Wuhan University from January to December in 2023 and met the admission criteria were selected as the research subjects. The subjects were examined by demography, anthropometry, laboratory tests and liver instantaneous elastography. The Chi-square test, t-test, one-way analysis of variance, Mann-Whitney U test and Kruskal-Wallis H test were used to compare the indexes between the subjects with and without MAFLD. The subjects were divided into 4 groups (Q1-Q4 groups) according to the RC/HDL-C ratio quartiles by quartile method, and the indexes in each group were compared. The receiver operating characteristic (ROC) curves were drawn using MedCalc software and compared to assess the diagnostic efficacy of the RC/HDL-C ratio for MAFLD. Results:With the increase of RC/HDL-C ratio, the detection rate of MAFLD (12.56% vs 43.48%), male proportion (55.68% vs 85.60%), total cholesterol (TC) [(4.63±0.82) vs (5.10±1.06) mmol/L], triglyceride (TG) [0.90(0.71, 1.15) vs 2.58(1.96, 3.50) mmol/L], alanine aminotransferase (ALT) [17.00(13.00, 24.00) vs 26.00(19.00, 38.00) U/L], aspartate aminotransferase (AST) [20.00(17.00, 24.00) vs 23.00(19.00, 29.00) U/L], and controlled attenuation parameter (CAP) [(239.32±40.52) vs (274.60±44.98) dB/m] increased gradually, while high-density lipoprotein cholesterol (HDL-C) [1.40(1.20, 1.64) vs 0.93(0.84, 1.04) μmol/L] decreased gradually (all P<0.05). ROC curves showed that the AUC value of RC/HDL-C ratio was significantly higher in identifying MAFLD when compared with TC, HDL-C, LDL-C, non-HDL-C and RC (AUC=0.676, P<0.05). Conclusions:The RC/HDL-C ratio is positively correlated with the risk of morbidity of MAFLD in health check-up population.
6.A prospective study of the effect of physical activity on mortality risk in patients with chronic obstructive pulmonary disease in Sichuan Province
Ying ZHANG ; Xiaofang CHEN ; Xiaofang CHEN ; Xia WU ; Xiaoyu CHANG ; Zhuo WANG ; Xu HAN ; Jun LYU ; Canqing YU ; Pei PEI ; Dianjianyi SUN ; Xianping WU
Chinese Journal of Epidemiology 2025;46(8):1347-1353
Objective:To investigate the effect of physical activity on mortality risk in patients with chronic obstructive pulmonary disease (COPD) in Sichuan Province.Methods:Based on baseline data from 2004 to 2008 from the China Kadoorie Biobank project site in Pengzhou City, Sichuan Province, a total of 8 501 COPD patients aged 30-79 years were enrolled and followed up for a long period to determine mortality outcomes. Quartiles were used to group physical activity levels. The Cox proportional hazards regression model was used to analyze the effect of physical activity level on mortality outcomes.Results:As of December 31, 2017, the cumulative follow-up of the participants totaled 85 600.58 person-years (mean follow-up duration: 10.07 years). During this period, a total of 2 000 deaths were recorded, yielding a cumulative mortality rate of 23.53%. Among these deaths, 665 were attributed to COPD, corresponding to a cumulative mortality rate of 7.82%; and 1 116 were attributed to cardiovascular and cerebrovascular disease (CVD), corresponding to a cumulative mortality rate of 13.13%. The Cox proportional hazards regression model analysis revealed that, after adjusting for confounding factors, total physical activity was associated with a reduced risk of mortality from COPD, CVD, and all causes in patients with COPD. Compared with the low-level group of total physical activity, the medium-high-level group had the lowest risk of COPD mortality, with an HR of 0.39 (95% CI: 0.30-0.49). The high-level group had the lowest risk of CVD death and all-cause death, with HRs of 0.46 (95% CI: 0.37-0.56) and 0.55 (95% CI: 0.48-0.64), respectively. The lowest risk of COPD death and CVD death was found in the medium-high level of work-based physical activity group, with HRs of 0.36 (95% CI: 0.28-0.46) and 0.43 (95% CI: 0.36-0.51), respectively; the risk of all-cause mortality was lowest in the medium-high and high-level groups, with HRs values of 0.53 (95% CI: 0.46-0.61) and 0.53 (95% CI: 0.45-0.61). The risk of COPD death was lowest in the high-level transportation physical activity group, with an HR of 0.66 (95% CI: 0.53-0.83), and the risk of CVD and all-cause death was lowest in the medium-high level group, with HRs of 0.63 (95% CI: 0.53-0.76) and 0.73 (95% CI: 0.64-0.84), respectively. The risk of COPD death and CVD death was the lowest in the high-level domestic physical activity group, with HRs of 0.66 (95% CI: 0.49-0.89) and 0.76 (95% CI: 0.61-0.95), respectively, and the risk of all-cause death was the lowest in the medium-high level group, with an HR of 0.82 (95% CI: 0.72-0.94). There is no statistical association between leisure physical activity and the risk of death from three types of diseases. Conclusions:Total physical activity, including work-based, transportation-based, and domestic physical activity, reduced the risk of COPD, CVD, and all-cause mortality in patients with COPD in Sichuan Province. The magnitude of mortality risk was influenced by the type and level of physical activity.
7.Learning curves of normal real-life vaginal delivery for residents in department of obstetrics and gynecology
Yan XU ; Jun GUAN ; Chang-en XU ; Qing-ying ZHANG ; Xian XIA
Fudan University Journal of Medical Sciences 2025;52(4):544-549
Objective To investigate the learning curve of real-life vaginal delivery,including its difficult steps and influencing factors,to optimize the future training of vaginal delivery for residents in department of obstetrics and gynecology.Methods From 25 Sep 2020 to 12 Mar 2022,OBGYN residents without previous experiences in vaginal delivery were prospectively enrolled in Obstetrics and Gynecology Hospital,Fudan University.Residents performed normal vaginal delivery under the supervision of senior obstetricians and midwives.The performance score(PS)of vaginal delivery and its 9 steps were evaluated via a questionnaire fulfilled by the supervisor once each delivery was finished.Logistic regression models were performed for univariate and multivariate analyses to evaluate the factors that might be correlated with the PS.Results Eventually,233 deliveries performed by 60 residents were analyzed.Results showed that more than 10 deliveries were needed for 70%of residents to obtain minimal competence of vaginal delivery.Perineal protection,delivery of the fetal head,delivery of the fetal shoulders and repair of episiotomy or laceration were found to be the most difficult steps,which required more practices to achieve minimal competence level.Univariate analyses showed the delivery experience,the times of observation/simulation/training,and humanistic care skills might influence the total PS(P<0.05).However,only delivery experience(OR=1.43,95%CI:1.22-1.67)and the times of observation(OR=1.02,95%CI:1.00-1.04)were found to be independently correlated with the total PS in multivariate analyses.Conclusion More than 10 real-life practices were required to achieve the minimal competence of normal vaginal delivery.Enhancing the training on the four difficult steps of vaginal delivery might improve the learning efficiency when delivery opportunities are limited.
8.Construction of Human-derived Chondrocyte PIEZO2 Overexpressing Cell Line and Identification of Osteoarthritis Phenotype
Bo-Yang XU ; Yi-Fei FAN ; Yu-Qing DU ; Meng-Ze SUN ; Jun-Yan WANG ; Jin CHENG ; Ying-Fang AO ; Xiao-Qing HU
Chinese Journal of Biochemistry and Molecular Biology 2025;41(6):871-878
To investigate the molecular mechanisms underlying the mechanosensitive ion channel PI-EZO2 in osteoarthritis(OA),we developed a lentiviral vector for endogenous PIEZO2 overexpression and established a stable PIEZO2-high-expressing immortalized human primary chondrocyte line.By map-ping the open reading frame of the PIEZO2 locus and designing sequence-specific sgRNA,we employed the CRISPR/Cas9 synergistic activation mediator(SAM)system to precisely integrate transcriptional ac-tivation elements into the PIEZO2 promoter region.Lentiviral-mediated targeted genomic integration en-sured endogenous PIEZO2 overexpression,confirmed by mCherry fluorescence tracing coupled with flow cytometric sorting,which revealed membrane-specific localization of PIEZO2 protein(localization effi-ciency:78.49%).Quantitative PCR demonstrated a 17-fold upregulation of PIEZO2 mRNA,while Western blotting validated enhanced membrane-localized protein expression.Strikingly,PIEZO2-overex-pressing chondrocytes exhibited hallmark OA metabolic phenotypes compared to wild-type controls:typeⅡ collagen mRNA expression decreased to 50%of baseline levels,whereas matrix metalloproteinase 13(MMP13)mRNA surged by 20-fold.These alterations recapitulated the pathological matrix metabolic phenotype observed in biomechanical OA models induced by cyclic mechanical stress(10%strain,0.5 Hz,8 h/day for 2 consecutive days).Collectively,we successfully generated a human chondrocyte model with stable PIEZO2 overexpression,which faithfully mirrors mechanotransduction-driven OA progression.This engineered cellular system provides a robust platform for dissecting PIEZO2-mediated mechanosig-naling networks and advancing targeted therapeutic discovery.
9.Expert Consensus on the Ethical Requirements for Generative AI-Assisted Academic Writing
You-Quan BU ; Yong-Fu CAO ; Zeng-Yi CHANG ; Hong-Yu CHEN ; Xiao-Wei CHEN ; Yuan-Yuan CHEN ; Zhu-Cheng CHEN ; Rui DENG ; Jie DING ; Zhong-Kai FAN ; Guo-Quan GAO ; Xu GAO ; Lan HU ; Xiao-Qing HU ; Hong-Ti JIA ; Ying KONG ; En-Min LI ; Ling LI ; Yu-Hua LI ; Jun-Rong LIU ; Zhi-Qiang LIU ; Ya-Ping LUO ; Xue-Mei LV ; Yan-Xi PEI ; Xiao-Zhong PENG ; Qi-Qun TANG ; You WAN ; Yong WANG ; Ming-Xu WANG ; Xian WANG ; Guang-Kuan XIE ; Jun XIE ; Xiao-Hua YAN ; Mei YIN ; Zhong-Shan YU ; Chun-Yan ZHOU ; Rui-Fang ZHU
Chinese Journal of Biochemistry and Molecular Biology 2025;41(6):826-832
With the rapid development of generative artificial intelligence(GAI)technologies,their widespread application in academic research and writing is continuously expanding the boundaries of sci-entific inquiry.However,this trend has also raised a series of ethical and regulatory challenges,inclu-ding issues related to authorship,content authenticity,citation accuracy,and accountability.In light of the growing involvement of AI in generating academic content,establishing an open,controllable,and trustworthy ethical governance framework has become a key task for safeguarding research integrity and maintaining trust within the academic community.This expert consensus outlines ethical requirements across key stages of AI-assisted academic writing-including topic selection,data management,citation practices,and authorship attribution.It aims to clarify the boundaries and ethical obligations surrounding AI use in academic writing,ensuring that technological tools enhance efficiency without compromising in-tegrity.The goal is to provide guidance and institutional support for building a responsible and sustainable research ecosystem.
10.Learning curves of normal real-life vaginal delivery for residents in department of obstetrics and gynecology
Yan XU ; Jun GUAN ; Chang-en XU ; Qing-ying ZHANG ; Xian XIA
Fudan University Journal of Medical Sciences 2025;52(4):544-549
Objective To investigate the learning curve of real-life vaginal delivery,including its difficult steps and influencing factors,to optimize the future training of vaginal delivery for residents in department of obstetrics and gynecology.Methods From 25 Sep 2020 to 12 Mar 2022,OBGYN residents without previous experiences in vaginal delivery were prospectively enrolled in Obstetrics and Gynecology Hospital,Fudan University.Residents performed normal vaginal delivery under the supervision of senior obstetricians and midwives.The performance score(PS)of vaginal delivery and its 9 steps were evaluated via a questionnaire fulfilled by the supervisor once each delivery was finished.Logistic regression models were performed for univariate and multivariate analyses to evaluate the factors that might be correlated with the PS.Results Eventually,233 deliveries performed by 60 residents were analyzed.Results showed that more than 10 deliveries were needed for 70%of residents to obtain minimal competence of vaginal delivery.Perineal protection,delivery of the fetal head,delivery of the fetal shoulders and repair of episiotomy or laceration were found to be the most difficult steps,which required more practices to achieve minimal competence level.Univariate analyses showed the delivery experience,the times of observation/simulation/training,and humanistic care skills might influence the total PS(P<0.05).However,only delivery experience(OR=1.43,95%CI:1.22-1.67)and the times of observation(OR=1.02,95%CI:1.00-1.04)were found to be independently correlated with the total PS in multivariate analyses.Conclusion More than 10 real-life practices were required to achieve the minimal competence of normal vaginal delivery.Enhancing the training on the four difficult steps of vaginal delivery might improve the learning efficiency when delivery opportunities are limited.

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