INTRODUCTION
The prevalence of pregnancies with breech presentation is approximately the same globally, involving 2%–4% of all deliveries.[1,2] It is also stated in some countries of the world 8.2%.[3] A breech presentation occurs with more perinatal mortality and short-term morbidity than vertex presentation, so perinatal mortality is increased 2–4 fold with a breech presentation.[4] Several risk factors are well described in the literature for breech presentation, including foetal abnormalities, placenta previa, uterine abnormalities, uterine leiomyoma, prematurity, multiple gestations, older maternal age, primiparity, lower foetal, previous caesarean section, weight, lower gestational age at delivery, maternal hip deformities and oligohydramnios.[1,3,5]
Although the literature suggests that several maternal and foetal abnormalities are associated with an elevated risk of breech presentation,[4] it is not clear which one risk factors have an effect on breech presentation.[4] It is possible that pregnancies with breech presentation are associated with placenta previa.[6] Thus, placenta previa can cause malpresentation and increase the risk of placental failure-related pregnancy complications.[7] Indeed, placenta previa has been related to pre-eclampsia, hypertension, uterine leiomyoma, smoking, intrauterine growth restriction, placental abruption and perinatal mortality.[7–9]
The literature lacks studies on the risk factors of breech presentation in pregnancies. It remains unclear whether the breech presentation is associated with placenta previa.[10] Most of the studies review placenta previa for caesarean section in pregnancies. Our hypothesis is that placenta previa is a risk factor associated with breech presentation at pregnancies. A consistent and strong estimate for this association can be achieved using a comprehensive meta-analysis by reviewing similar studies. Therefore, we performed a systematic review and meta-analysis to summarise the epidemiologic evidence of the association between placenta previa and increased risk of breech presentation.
METHODS
Data sources
This meta-analysis was measured the association between placenta previa and the risk of the breech presentation. Based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses checklist, this meta-analysis was completed. We have done a search for appropriate studies in key databases, including Web of Science, PubMed, Science Direct and Scopus, irrespective of race, country, publication date and language of articles.
Criteria for including and excluding studies
All articles that reported an association between placenta previa and the risk of the breech presentation using systematic search were included. All full articles were reread by two researchers.
Search methods
One author conducted the complete search strategy in PubMed, Scopus, Science Direct and Web of Science databases using keywords: (placenta previa or placental previa) and (breech presentation odds ratio [OR] malpresentation or breech birth). The following search was directed up to April 2020. References of the related meta-analysis were reviewed for searching for new articles. Furthermore, we searched the grey literature.
Data collection and validity assessment
The initial review was directed by two independent researchers, and differences were resolved. The included data were the year of publications, first author, OR and their associated 95% confidence intervals (CI), country, the study design of studies, sample size, adjustment, diagnose method for placenta previa, maternal age (mean or range) and the quality assessment of articles.
The qualities of papers were assessed using the Newcastle-Ottawa scale (NOS).[11] After scoring, the studies were classified into two groups low-quality studies (scoring <7 points) and high-quality studies (scoring ≥7 points).[12]
Statistical analysis
Heterogeneity in included articles was discovered using I2 statistic. Data were analysed, and the consequences were shown by the random-effect model.[13] The publication bias tests were Begg and Egger’s in extracted articles.[14] All meta-analysis was carried out by Stata software version 14 (Release 14. College Station, TX: StataCorp LP).
RESULTS
An overall of 466 studies was obtained finished search in the above-mentioned databases and hand searching. Of these studies, 245 were excluded during duplicate publications. In the screening using title and abstract, 203 studies were excluded during not assembly the selection criteria. In the second valuation, ten studies were excluded based on the full-text valuation. Consequently, eight articles were included in the meta-analysis [Figure 1]. Of these articles, one was a cross-sectional study,[10] two were case–control studies[15,16] and five were cohort studies.[1,17–20] The publication year for studies was from 1996 to 2020. All articles were in the English language. The overall number of participants in these articles was 1,972,511.
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Figure 1: Flow of information in the systematic review and meta-analysis
Effects of exposure
Figure 2 shows the relationship between placenta previa and the risk of breech presentation. There was a significant association between placenta previa and the risk of breech presentation based on adjusted studies (OR = 1.93; 95% CI: 1.09, 2.76). The results were heterogeneous (I2 = 81.4%, P = 0.001) [Figure 2].
Figure 2: Forest plot of the association between placenta previa and the risk of breech presentation
Moreover, there was not a statistically significant association between placenta previa and the risk of breech presentation according to crude studies (OR = 1.64; 95% CI: 0.74, 2.54). There was heterogeneity between the findings (I2 = 93.3%, P = 0.001) [Figure 2].
Publication bias
Begg and Egger’s tests were applied to measure the publication bias between studies. There was no publication bias amongst studies by Begg and Egger tests (P = 0.216 and P = 0.066, respectively).
Quality of the studies
Based on the NOS scale, eight articles were of high quality [Table 1].
Table 1: Summaries of included studies in present meta-analysis
DISCUSSION
This study shows that placenta previa is associated with the risk of breech presentation in pregnancies in adjusted studies. There was heterogeneity amongst included studies in the present meta-analysis. Therefore, placenta previa should be considered a risk factor in pregnancies as well as a sign of future risk of the breech presentation.
These are in line with the findings of previous studies[6,21] that associated placenta previa with breech presentation. Maternal factors related to breech presentation include contracted maternal pelvis, uterine anomalies, nulliparity, use of anticonvulsant drugs, multiparity, previous breech birth, cornual placenta and especially placenta previa.[22]
Another study showed that breech presentation is related to congenital abnormalities and uterine and has a major recurrence risk.[23] Furthermore, a study found a significant increase in mortality amongst infants due to breech presentation.[24] The specific contribution of breech presentation to term perinatal mortality rates has been recognised,[10] so breech presentation in term delivery is an independent risk factor for neonatal mortality.[10]
The placenta previa occupies the inferior segment of the uterine cavity. Therefore, the presenting part cannot engage, and this issue can lead to breech presentation.[6]
Breach presentation increases the risk of caesarean section at the end of pregnancy.[25] The majority of these mothers will deliver through caesarean section, which has great charges and increased risk of morbidity and mortality for both child and women.[25] Such evidence recommends that caesarean delivery may have long-term outcomes on the health of the women and the child and future pregnancies, such as the increased risk of placenta previa.[26,27] Consistently, women with placenta previa had the risk of higher caesarean delivery.[28] This can be described by the detail that the placenta previa in the lower segment obstructs the visit of the head.
To our knowledge, this was the first study to appraisal the association between placenta previa and the risk of breech presentation to help recognise knowledge gaps.
Some limitations need to be recognised in our meta-analysis. Heterogeneity amongst included studies was high. Furthermore, some studies reported only the crude form of OR. Therefore, these might introduce information bias in our results. However, our meta-analysis with 1,972,511 participants showed that previa is a risk factor for breech presentation. Pregnant women should be vigorously visited for a history of placenta previa as per part of preventive care or in appraisal for breech presentation risk. Using this information is essential in the first phase to risk stratification and recognise outcomes.
To our knowledge, this was the first study that showed placenta previa is a risk factor for breech presentation. Additional studies are necessary to recognise which mothers with a history of placenta previa are at increased risk of breech presentation.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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