Impact factor (WEB OF SCIENCE - Clarivate)

2 year: 7.2 | 5 year: 6.6

Articles

Prevalence of placenta previa among deliveries: An update systematic review and meta-analysis after the introduction of the two-child policy in Mainland China

Dazhi Fan1,2, Yushi Liu2,3, Pengzhen Hu2,3, Dongxin Lin1, Jiaming Rao1, Li Sun4, Wen Wang2, Linlin Wu2, Li Liu5, Yubo Ma6, Zhengping Liu1,2, Xiaoling Guo1,2,3

1 Foshan Fetal Medicine Research Institute, Foshan Women and Children Hospital, Foshan, Guangdong, China
2 Department of Obstetrics, Foshan Women and Children Hospital, Foshan, Guangdong, China
3 The Second School of Clinical Medicine, Southern Medical University, Guangzhou, Guangdong, China
4 Department of Library, Foshan Women and Children Hospital, Foshan, Guangdong, China
5 Department of Library, First Affiliated Hospital, College of Medicine, Zhejiang University, Hangzhou, Zhejiang, China
6 Department of Epidemiology and Biostatistics, School of Public Health, Anhui Medical University, Hefei, Anhui, China

DOI: 10.7189/jogh.14.04108

Share:

Facebook
Twitter
LinkedIn
Abstract

Background

As birth policy can affect maternal and infant health, we sought to identify whether and how the introduction of the two-child policy might have affected the prevalence of placenta previa in pregnant women in mainland China.

Methods

In this update meta-analysis and systematic review, we searched PubMed, Web of Science, the Cochrane Library, Weipu, Wanfang, and the China National Knowledge Infrastructure (CNKI) databases for studies evaluating the prevalence of placenta previa in China published between the inception of each database and March 2024, with no restrictions. Two investigators independently extracted the data from each included study. We then combined the prevalence of placenta previa using random-effects models.

Results

We included 128 studies in our analysis, 48 more than in our previous review. The prevalence of placenta previa among Chinese pregnant women was 1.44% (95% confidence interval (CI) = 1.32, 1.56). After the implementation of the two-child policy, the prevalence increased significantly, from 1.25% (95% CI = 1.16, 1.34) to 4.12% (95% CI = 3.33, 4.91).

Conclusions

The prevalence of placenta previa increased significantly from the one-child policy period to the two-child policy period among mainland Chinese pregnant women, with varying trends across regions. This change requires the attention of health officials and timely adjustment of resource allocation policies.

Registration

PROSPERO: CRD42021262309.

Print Friendly, PDF & Email

Placenta previa is a potentially severe obstetric complication where the placenta overlying the endocervical os [1,2]. According to a systematic review from 2013, its prevalence varies widely between countries and regions, ranging between 12.2‰ in Asia, 3.6‰ in Europe, 2.9‰ in North America, and 2.7‰ in sub-Saharan Africa [3]. Moreover, in our 2016 systematic review and meta-analysis of 80 studies that collected data between 1965 and 2015, we observed that the prevalence of placenta previa was 1.24% in mainland China, with likewise unequal geographic distribution, ranging from 2.90% in Hainan to 0.54% in Liaoning [4].

Many maternal and foetal factors are associated with placenta previa, including maternal behavioural and sociodemographic characteristics, endometrial disease or injury, and delayed development of the fertilised egg trophoblast [57]. The prevalence of placenta previa has increased rapidly worldwide in recent years, likely due to increases in the rates of advanced maternal age and the number of caesarean sections [8,9].

Some studies have shown that the change of birth policy is associated with increases in the proportion of advanced maternal age and assisted reproductive pregnancy, which in turn might exacerbate maternal and infant health risks [1013]. In October 2015, China introduced the two-child policy [14], which over time led to increases in the number of women of advanced maternal age; women who had undergone caesarean sections or had uterine scars; women who used assisted reproductive technology, and women who had multiple pregnancies [1518]. Previous studies have shown that these factors might increase the risk of adverse pregnancy complications, including placenta previa [1923].

The temporal changes and trends of placenta previa in Chinese pregnant women need to be better understood, especially after the implementation of the two-child policy. Such data could inform current and future health care planning, as well as help identify and forecast unmet medical needs in this context. Moreover, by modifying their obstetric service strategies within the framework of the new two-child policy, hospitals could decrease adverse pregnancy outcomes and improve the quality of perinatal health care.

However, there is currently a lack of data on and no systematic analysis of the prevalence of placenta previa among Chinese pregnant women before and after the implementation of the universal two-child policy. Our study aimed to identify the prevalence and main risk factors for placenta previa following the implementation of the universal two-child policy by updating our previous meta-analysis and systematic review. We hypothesised that the prevalence of placenta previa would show an increasing trend and that its geographical distribution would change with the introduction of the two-child policy.

METHODS

We registered the original protocol of our previous study within PROSPERO (CRD42021262309) and reported our findings per the MOOSE and PRISMA guidelines [24,25].

Search strategy

For this updated review, we searched Web of Science, the Cochrane Library, PubMed, Weipu, Wanfang, and the China National Knowledge Infrastructure (CNKI) databases for studies that evaluated placenta previa prevalence and were published between inception and March 2024. We set no restrictions on language. With the help of two biomedical librarians (LS and LL), we designed our search around the following keywords: ‘placenta previa’ AND ‘Chinese’ AND ‘prevalence’ (File S1 in the Online Supplementary Document). Following deduplication, DF and DL screened the retrieved records to identify studies meeting our inclusion criteria.

Eligibility criteria

As in our previous review [4], we included observational studies (cross-sectional, cohort studies, and case-control) on placenta previa among pregnant women meeting the clinical diagnostic criteria [26,27] conducted in mainland China, providing they reported the prevalence or incidence of placenta previa. We excluded meeting abstracts; case reports and case series; poster presentations; and articles we could not access or that had incomplete data.

Data extraction

At least two of seven investigators (DF, LL, YL, JR, LS, PH, and WW) independently extracted the following data for each study: author, design, year of publication, sample sizes, prevalence estimates, and associated risk factors. An independent investigator (JR) verified all the extracted data. We resolved discrepancies during data extraction by discussion or adjudication by a third investigator (XG) where needed.

Methodological quality assessment

In line with our previous reviews and similar studies [4,2830], two investigators (DF and DL) independently assessed the risk of bias in each included study using the STROBE checklist [31] (Table S2 in the Online Supplementary Document). This assessment was based on five modules: sample population, sample size, participation rate, outcome assessment, and analytical methods. Each module was scored as 0 for high risk and unclear, 1 for moderate risk, and 2 for low risk, with the sum of the scores for all five modules indicating the overall bias risk of each study. We resolve discrepancies during the risk of bias assessment by discussion or adjudication by a third investigator (JR) where needed.

Statistical analysis

The primary outcome was the prevalence of placenta previa among Chinese pregnant women. We collected raw data from every study to recalculate prevalence and their associated standard errors, using the mid-year as the reference for point prevalence when multiple years were included in the study period. We then used the I2 statistic to assess the heterogeneity between included studies: I2 values of 0–50%, 50–75%, and >75% were considered as low, moderate, and high, respectively. We used a random effects model for cases where I2 was ≥50%; otherwise, we used a fixed effects model [3235].

Due to the anticipated heterogeneity, we used random effects models to calculate the overall and subgroup pooled prevalence estimates [30,36]. Meanwhile, we conducted subgroup and meta-regression (univariate and multivariable) analyses to explore potential sources of heterogeneity. Based on the studies included in our previous review and other similar prevalence meta-analyses [3,4,17,18], the potential variables were geographical study region, survey year, quality score, maternal age, and hospital level. Lastly, we used funnel plots and Egger’s test to assess small-study effects. We performed all analyses in Stata, version 12.0 (StataCorp LLC, College Station, TX, USA). Statistical significance was set at P < 0.05.

To investigate the impact of the two-child policy, we analysed the data on the prevalence of placenta previa after 2016, i.e. after the year of the implementation of the two-child policy. To determine the geographical differences in the prevalence of placenta previa, we generated a map of pooled prevalence in each province through ArcGIS, version 10 (Environmental Systems Research Institute, Redlands, California) system [37] after calculating the pooled prevalence for each province through a meta-analysis.

RESULTS

Literature search

We identified 536 non-duplicate records in the database search; 349 were ineligible by title and abstract review and an additional 59 upon full-text review. We therefore included 128 observational studies (Figure 1).

Figure 1.  Flow diagram of the selection process.

We included 48 more studies in this update compared to our previous review. Of the total 3 532 258 pregnant women within the included studies (with sample sizes ranging from 701 to 267 834), 47 285 had placenta previa. The included studies encompassed all provinces of mainland China, with 30 studies conducted in East China, 26 in the South China, 22 in North China, 16 in Southwest China, 15 in Central China, 11 in Northeast China, and 9 in Northwest China. Ten studies were conducted after the implementation of the two-child policy (Table S1 in the Online Supplementary Document).

Quality assessment

The median quality assessment rating was 5 (interquartile range = 5–7). Of the 128 studies that reported prevalence of placenta previa, 11 (8.6%) scored 9 points, 13 (10.2%) scored 8 points, 13 (10.2%) scored 7 points, 28 (21.9%) scored 6 points, 48 (37.5%) scored 5 points, and 15 (11.7%) scored 4 points (Table S2 in the Online Supplementary Document).

Overall prevalence of placenta previa

The overall pooled prevalence of placenta previa was 1.44% (95% confidence interval (CI) = 1.32, 1.56). The prevalence of placenta previa increased significantly after the implementation of the two-child policy, from 1.25% (95% CI = 1.16, 1.34) in the prior period to 4.12% (95% CI = 3.33, 4.91) after the implementation (Table 1).

Table 1.  Prevalence of placenta previa in mainland China and subgroup analysis

CI – confidence interval

Subgroup analysis

At the regional level, the prevalence of placenta previa was the highest in Southwestern China (2.34%), followed by Central China (1.57%), South China (1.46%), Northeast China (1.30%), East China (1.18%), North China (1.17%), and Northwest China (1.13%). In the province-level analysis, we observed the highest prevalence in Hainan (2.90%), and the lowest in Xinjiang (0.43%) (Figure S1 and Table S3 in the Online Supplementary Document). In the subgroup analysis by year, the prevalence of placenta previa fluctuated slightly around 1.20% prior to 2015, except for 1993 (2.99%). Afterwards, the prevalence increased to 3.57% in 2016, 4.50% in 2017, 3.34% in 2018, and 4.84% in 2019 (Figure 2). We also observed that the prevalence of placenta previa increased with maternal age, from 1.23% at <25 years of age, to 1.27% at 25–30 years of age, and lastly to 1.68% at >30 years. At the hospital level, we observed the prevalence of placenta previa was 1.66% in tertiary hospitals, 1.36% in secondary hospitals, and 1.22% in primary hospitals. By quality score, the prevalence of placenta previa was significantly higher in the 6–10 scores group (1.62%) than in the 0–5 scores group (1.23%) (Table 1).

Figure 2.  Trends in the prevalence of placenta previa.

Meta-regression analysis

Univariable meta-regression analyses showed that the implementation of the two-child policy and survey year were potential sources of heterogeneity. Multivariable analyses confirmed these findings and further showed that the two-child policy has the greatest influence on the result (Table 2).

Table 2.  Meta-regression analysis on the included studies

CI – confidence interval

DISCUSSION

In this updated systematic review and meta-analysis based on pooled results from 128 studies involving 3 532 258 participants, we found the prevalence of placenta previa in mainland China to be 1.44%. We also observed a significant difference in the prevalence of placenta previa in the period before compared to the period after the implementation of the two-child policy (1.25% vs 4.12%), confirming our hypothesis that it increased the risk of placenta previa.

This is our second, updated meta-analysis assessing the prevalence of placenta previa in pregnant women in mainland China. In the previous review, we included 80 studies published before 2015, meaning they only included the period before the two-child policy [4]. Therefore, we were unable to assess the impact of the birth policy changes on placenta previa at that time.

While our main findings are consistent with our previous meta-analysis, meaning we again observed that the prevalence of placenta previa significantly varied across mainland China, this update included a higher number of studies and enabled us to conduct a separate analysis for the period after the two-child policy was implemented. Here we found that, in contrast to the minor fluctuations observed in the previous study, the prevalence of placenta previa increased sharply in the post-implementation period.

Since the introduction of the new two-child policy, the rates of advanced maternal age, multiparous women, history of caesarean section, and pregnancy complications increased in mainland China, leading to an increase in the rate of adverse pregnancy outcomes [10,16,21,38], leading to an increase in adverse pregnancy outcomes. With the further broadening of China’s childbearing policy, pregnancy complications – including placenta previa – will likely continue to rise, necessitating the attention of governmental institutions, including through early planning and prevention, increasing the number of obstetricians, and the establishment of high-standard regional maternity treatment centres.

Our analysis of geographical distribution showed that the prevalence has increased in all regions after the implementation of the two-child policy, with some distinct differences between regions. However, at this level, there has been no significant change in the relative prevalence of placenta previa compared to the period before the implementation of the policy. Specifically, we again observed that Hainan and Liaoning had the highest and lowest prevalence of placenta previa, respectively, compared to the other areas. These significant regional variations in placenta previa rates and trends may be related to the differences in geography, economy, living conditions, and other factors like patient preferences and health care systems. Simultaneously, the implementation of the two-child policy has also increased the occurrence of placenta previa through the impact of risk factors.

Like in other meta-analyses of the prevalence of placenta previa [3,28,29], we observed high heterogeneity between studies, which was not explained by our subgroup analyses of geographical study regions, survey years, quality scores, maternal age, and hospital levels. We propose that other factors, such as maternal behaviours, lifestyle habits, alcohol or coffee consumption, sociodemographic characteristics, and mental and physical inactivity may have influenced this heterogeneity. However, due to limited data on these factors, we were unable to carry out further analyses. We advise that our results are interpreted through the 95% CIs rather than the pooled result due to the high level of heterogeneity.

We also performed univariable and multivariable meta-regression analyses to further explore the size and the source of this heterogeneity. Our findings suggest that the survey year and the implementation of the two-child policy were significantly associated with the prevalence of placenta previa. Notably, the studies in our analysis were conducted between 1965 and 2023. During this nearly 60-year period, maternal behaviours, lifestyle habits, and sociodemographic characteristics of the participants have changed greatly, as did health care and reporting practices, as well as the criteria and methods for diagnosing of placenta previa.

Moreover, previous evidence indicated that the rates of advanced maternal age, women with prior caesarean sections and uterine scars, assisted reproductive technology interventions, and multiparous women were significantly increased after the implementation of the two-child policy [17,18]. The risk of placenta previa is likely significantly higher in women who experience these conditions or interventions, which will likely lead to a hike in the incidence of placenta previa in this population. This partly explains why the meta-regression analyses suggested that the two-child policy had the highest impact on the heterogeneity.

Placenta previa is a complex clinical and public health issue that both impacts the health of pregnant women and their offspring and contributes to a significant increase in the national disease burden [3941]. The main contribution of our findings is a detailed representation of the currently alarming state of placenta previa, which could inform and alert decision-makers and practitioners in the health care sector in China – especially as the increase in the number of pregnant women at high risk of placenta previa will further exacerbate these challenges. Meanwhile, individuals, families, communities, and hospitals should also strive towards a multisectoral collaboration to ensure the safety of pregnant women with placenta previa.

The main strengths of this meta-analysis are its relatively large sample size and its novel estimates of the prevalence of placenta previa in pregnant women in mainland China after the implementation of the two-child policy. Of course, our findings must be interpreted in the context of the limitations of our study. Specifically, we observed high between-study heterogeneity in the analysis of placenta previa prevalence due to differences in the study years and regions. Moreover, as newer studies are yet to be published, we have only included 10 articles after the two-child policy, which may have affected the stability of our results, especially for the periods after this policy was implemented. Future studies could provide more data to address this gap. Moreover, this study only focussed on the change in the prevalence of placenta previa after two-child policy was implemented. We leave other specific clinical and public health issues for future studies, such as longitudinal studies assessing the long-term impact of the two-child policy on maternal health outcomes.

CONCLUSIONS

The prevalence of placenta previa increased significantly from the one-child policy period to the two-child policy period among pregnant women in mainland China, with distinct variations across regions. This necessitates the attention of health officials and timely adjustment of resource allocation policies. Our findings provide a stronger basis for understanding the impact of policy changes on placenta previa prevalence in mainland China. Accurate early prediction models are needed to improve individualised care for affected women, while an early maternal referral system could help them access immediate care and thereby ensure their safety, especially in lower-level hospitals.

Additional material

Online Supplementary Document.

Acknowledgments

We appreciate the efforts of all the researchers whose articles were included in this study.

Ethics statement: This study involved only a literature review of previously published studies and the data they contained. It involved no primary research on human or animal subjects, or medical records. As such, this work was considered exempt from ethical review.

Data availability: The study data are available from the corresponding author upon reasonable request.

[1] Funding: This work was supported by the 2022 Foshan self-funded Science and Technology Innovation Project (No. 2220001004010), and 2023 and 2024 Foshan Health Bureau Medical Scientific Research Project (No. 20230814A010028 and No. 20240720A010564).

[2] Authorship contributions: DF, and XG participated in the design and coordination of the study. DF conceived the study and drafted the manuscript. DF, LS, and LL searched the databases and checked the extracted studies per the inclusion and exclusion criteria. YL, YM, DL, LW, PH, WW, and JR help develop search strategies. DF, DL, and JR analysed the data. DF, ZL, and XG did the data management. All authors read and approved the final manuscript.

[3] Disclosure of interest: The authors completed the ICMJE Disclosure of Interest Form (available upon request from the corresponding author) and disclose no relevant interests.

references

[1] RM Silver. Abnormal Placentation: Placenta Previa, Vasa Previa, and Placenta Accreta. Obstet Gynecol. 2015;126:654-68. DOI: 10.1097/AOG.0000000000001005. [PMID:26244528]

[2] D Fan, H Zhang, J Rao, D Lin, S Wu, and P Li. Maternal and neonatal outcomes in transverse and vertical skin incision for placenta previa: Skin incision for placenta previa. BMC Pregnancy Childbirth. 2021;21:441 DOI: 10.1186/s12884-021-03923-1. [PMID:34167519]

[3] JA Cresswell, C Ronsmans, C Calvert, and V Filippi. Prevalence of placenta praevia by world region: a systematic review and meta-analysis. Trop Med Int Health. 2013;18:712-24. DOI: 10.1111/tmi.12100. [PMID:23551357]

[4] D Fan, S Wu, W Wang, L Xin, G Tian, and L Liu. Prevalence of placenta previa among deliveries in Mainland China: A PRISMA-compliant systematic review and meta-analysis. Medicine (Baltimore). 2016;95:e5107. DOI: 10.1097/MD.0000000000005107. [PMID:27749592]

[5] E Jenabi, Z Salimi, S Bashirian, S Khazaei, and E Ayubi. The risk factors associated with placenta previa: An umbrella review. Placenta. 2022;117:21-7. DOI: 10.1016/j.placenta.2021.10.009. [PMID:34768164]

[6] SY Long, Q Yang, R Chi, L Luo, X Xiong, and ZQ Chen. Maternal and Neonatal Outcomes Resulting from Antepartum Hemorrhage in Women with Placenta Previa and Its Associated Risk Factors: A Single-Center Retrospective Study. Ther Clin Risk Manag. 2021;17:31-8. DOI: 10.2147/TCRM.S288461. [PMID:33469297]

[7] J Rao, D Fan, Z Zhou, X Luo, H Ma, and Y Wan. Maternal and Neonatal Outcomes of Placenta Previa with and without Coverage of a Uterine Scar: A Retrospective Cohort Study in a Tertiary Hospital. Int J Womens Health. 2021;13:671-81. DOI: 10.2147/IJWH.S310097. [PMID:34262357]

[8] SPR Kanigalpula, A Murali, A Raveendranath, P Vadivelu, DK Maurya, and A Keepanasseril. Risk factors associated with unplanned caesarean section in women with placenta previa: a cohort study. J Obstet Gynaecol. 2022;42:1163-8. DOI: 10.1080/01443615.2022.2027892. [PMID:35152827]

[9] HT Li, S Hellerstein, YB Zhou, JM Liu, and J Blustein. Trends in Cesarean Delivery Rates in China, 2008-2018. JAMA. 2020;323:89-91. DOI: 10.1001/jama.2019.17595. [PMID:31910272]

[10] X Zhang, L Chen, X Wang, X Wang, M Jia, and S Ni. Changes in maternal age and prevalence of congenital anomalies during the enactment of China’s universal two-child policy (2013-2017) in Zhejiang Province, China: An observational study. PLoS Med. 2020;17:e1003047. DOI: 10.1371/journal.pmed.1003047. [PMID:32092053]

[11] J Yan, L Wang, Y Yang, Y Zhang, H Zhang, and Y He. The trend of caesarean birth rate changes in China after ‘universal two-child policy’ era: a population-based study in 2013-2018. BMC Med. 2020;18:249 DOI: 10.1186/s12916-020-01714-7. [PMID:32928217]

[12] M He, X Sun, C Wang, and Y Sui. Analysis of the risk of complications during pregnancy in pregnant women with assisted reproductive technology: a retrospective study using registry linkage from 2013 to 2018 in Shanghai, China. BMC Pregnancy Childbirth. 2022;22:526 DOI: 10.1186/s12884-022-04846-1. [PMID:35764962]

[13] F Bai, DY Wang, YJ Fan, J Qiu, L Wang, and Y Dai. Assisted reproductive technology service availability, efficacy and safety in mainland China: 2016. Hum Reprod. 2020;35:446-52. DOI: 10.1093/humrep/dez245. [PMID:32020190]

[14] Y Zeng and T Hesketh. The effects of China’s universal two-child policy. Lancet. 2016;388:1930-8. DOI: 10.1016/S0140-6736(16)31405-2. [PMID:27751400]

[15] Q Long, Y Zhang, J Zhang, X Tang, and C Kingdon. Changes in caesarean section rates in China during the period of transition from the one-child to two-child policy era: cross-sectional National Household Health Services Surveys. BMJ Open. 2022;12:e059208. DOI: 10.1136/bmjopen-2021-059208. [PMID:35418438]

[16] H Li, Nawsherwan, C Fan, S Yin, IU Haq, and S Mubarik. Changes in adverse pregnancy outcomes in women with advanced maternal age (AMA) after the enactment of China’s universal two-child policy. Sci Rep. 2022;12:5048 DOI: 10.1038/s41598-022-08396-6. [PMID:35322808]

[17] H Zhu, J Cai, H Liu, Z Zhao, Y Chen, and P Wang. Trajectories tracking of maternal and neonatal health in eastern China from 2010 to 2021: A multicentre cross-sectional study. J Glob Health. 2024;14:04069 DOI: 10.7189/jogh.14.04069. [PMID:38515427]

[18] ML Tian, GJ Ma, LY Du, Y Jin, C Zhang, and YG Xiao. The Effect of 2016 Chinese second-child policy and different maternal age on pregnancy outcomes in Hebei Province, China. BMC Pregnancy Childbirth. 2023;23:267 DOI: 10.1186/s12884-023-05552-2. [PMID:37076792]

[19] H Zhu, Z Zhao, J Xu, Y Chen, Q Zhu, and L Zhou. The prevalence of gestational diabetes mellitus before and after the implementation of the universal two-child policy in China. Front Endocrinol (Lausanne). 2022;13:960877. DOI: 10.3389/fendo.2022.960877. [PMID:36060951]

[20] K Deng, J Liang, Y Mu, Z Liu, Y Wang, and M Li. Preterm births in China between 2012 and 2018: an observational study of more than 9 million women. Lancet Glob Health. 2021;9:e1226-41. DOI: 10.1016/S2214-109X(21)00298-9. [PMID:34416213]

[21] F Zhao, Y Xu, YT Chen, JY Cheng, and XY Pan. Influence of the universal two-child policy on obstetric issues. Eur J Obstet Gynecol Reprod Biol. 2020;252:479-82. DOI: 10.1016/j.ejogrb.2020.07.028. [PMID:32758858]

[22] HT Li, M Xue, S Hellerstein, Y Cai, Y Gao, and Y Zhang. Association of China’s universal two child policy with changes in births and birth related health factors: national, descriptive comparative study. BMJ. 2019;366:l4680 DOI: 10.1136/bmj.l4680. [PMID:31434652]

[23] D Fan, D Lin, J Rao, P Li, G Chen, and Z Zhou. Factors and outcomes for placental anomalies: An umbrella review of systematic reviews and meta-analyses. J Glob Health. 2024;14:04013 DOI: 10.7189/jogh.14.04013. [PMID:38236697]

[24] DF Stroup, JA Berlin, SC Morton, I Olkin, GD Williamson, and D Rennie. Meta-analysis of observational studies in epidemiology: a proposal for reporting. Meta-analysis Of Observational Studies in Epidemiology (MOOSE) group. JAMA. 2000;283:2008-12. DOI: 10.1001/jama.283.15.2008. [PMID:10789670]

[25] MJ Page, JE McKenzie, PM Bossuyt, I Boutron, TC Hoffmann, and CD Mulrow. The PRISMA 2020 statement: an updated guideline for reporting systematic reviews. BMJ. 2021;372:n71 DOI: 10.1136/bmj.n71. [PMID:33782057]

[26] D Fan, J Rao, D Lin, H Zhang, Z Zhou, and G Chen. Anesthetic management in cesarean delivery of women with placenta previa: a retrospective cohort study. BMC Anesthesiol. 2021;21:247 DOI: 10.1186/s12871-021-01472-w. [PMID:34666687]

[27] D Fan, J Rao, H Zhang, D Lin, X Guo, and Z Liu. Blood Type and Outcomes in Pregnant Women with Placenta Previa. Oxid Med Cell Longev. 2023;2023:4725064. DOI: 10.1155/2023/4725064. [PMID:36743690]

[28] FJ Robles-Palazón, A López-Valenciano, M De Ste Croix, JL Oliver, A García-Gómez, and P Sainz de Baranda. Epidemiology of injuries in male and female youth football players: A systematic review and meta-analysis. J Sport Health Sci. 2022;11:681-95. DOI: 10.1016/j.jshs.2021.10.002. [PMID:34700052]

[29] Y Yuan, X Wang, Y Zhou, C Zhou, and S Li. Prevalence and risk factors of latent tuberculosis infection among college students: a systematic review and meta-analysis. Public Health. 2022;213:135-46. DOI: 10.1016/j.puhe.2022.10.003. [PMID:36410119]

[30] D Fan, S Li, S Wu, W Wang, S Ye, and Q Xia. Prevalence of abnormally invasive placenta among deliveries in mainland China: A PRISMA-compliant Systematic Review and Meta-analysis. Medicine (Baltimore). 2017;96:e6636. DOI: 10.1097/MD.0000000000006636. [PMID:28422862]

[31] E von Elm, DG Altman, M Egger, SJ Pocock, PC Gotzsche, and JP Vandenbroucke. The Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) statement: guidelines for reporting observational studies. Lancet. 2007;370:1453-7. DOI: 10.1016/S0140-6736(07)61602-X. [PMID:18064739]

[32] T Yang, Z Duan, S Wu, S Liu, Z Zeng, and G Li. Association of HLA-B27 genetic polymorphisms with ankylosing spondylitis susceptibility worldwide: a meta-analysis. Mod Rheumatol. 2014;24:150-61. DOI: 10.3109/14397595.2013.852856. [PMID:24261772]

[33] W Wang, D Fan, J Wang, S Wu, Y Lu, and Y He. Association between hypertensive disorders complicating pregnancy and risk of placenta accreta: a meta-analysis and systematic review. Hypertens Pregnancy. 2018;37:168-74. DOI: 10.1080/10641955.2018.1498880. [PMID:30040502]

[34] C Guo, Y Ma, Y Situ, L Liu, G Luo, and H Li. Mesenchymal stem cells therapy improves ovarian function in premature ovarian failure: a systematic review and meta-analysis based on preclinical studies. Front Endocrinol (Lausanne). 2023;14:1165574. DOI: 10.3389/fendo.2023.1165574. [PMID:37484938]

[35] D Fan, Q Xia, D Lin, Y Ma, J Rao, and L Liu. Role of breastfeeding on maternal and childhood cancers: An umbrella review of meta-analyses. J Glob Health. 2023;13:04067 DOI: 10.7189/jogh.13.04067. [PMID:37350093]

[36] R DerSimonian and N Laird. Meta-analysis in clinical trials revisited. Contemp Clin Trials. 2015;45:139-45. DOI: 10.1016/j.cct.2015.09.002. [PMID:26343745]

[37] Environmental Systems Research InstituteHomepage. 2024. Available: http://www.esri.com. Accessed: 29 May 2024.

[38] HX Zhang, YY Zhao, and YQ Wang. Analysis of the Characteristics of Pregnancy and Delivery before and after Implementation of the Two-child Policy. Chin Med J (Engl). 2018;131:37-42. DOI: 10.4103/0366-6999.221268. [PMID:29271378]

[39] Z Liu, D Fan, D Lin, H Zhang, J Rao, and W Wang. Double-uterine-incision in the management of placenta previa complicated by placenta accreta spectrum. Am J Transl Res. 2021;13:13017-23. [PMID:34956519]

[40] LJ Wang, DZ Fan, HX Guo, BS Chen, and ZP Liu. Weight gain during pregnancy and placenta morphology: a prospective cohort study. Eur Rev Med Pharmacol Sci. 2022;26:1978-83. [PMID:35363348]

[41] JP Feng, DZ Fan, DX Lin, HS Zhang, JM Rao, and ZP Liu. Sandwich excision in patients with placenta percreta involving maternal bladder. Eur Rev Med Pharmacol Sci. 2022;26:4252-7. [PMID:35776024]

Correspondence to:
Dazhi Fan
Foshan Fetal Medicine Research Institute, Foshan Women and Children Hospital
11 Renminxi Road, Foshan, Guangdong, 528000
China
[email protected]
Xiaoling Guo
The Second School of Clinical Medicine, Southern Medical University
No.2 Lujing Road, Guangzhou, Guangdong, 510091
China
[email protected]