INTRODUCTION
The breech presentation happens in 3%–4% of all pregnancies. The prevalence of breech presentations decreases with increasing of gestational age so that breech presentation at term reach to 1%–3% of all births.[1]
Autism spectrum disorders (ASDs) are neurodevelopmental disorders with dysfunction of cognitive, behavioural and social. The aetiology of autism is unclear. There is evidence of contribute genetic and environmental factors in the aetiology of the disorder. Perinatal and postnatal factors are associated with increased risk of ASD.[2] There were some risk factors among maternal including maternal smoking, alcohol, preeclampsia, respiratory tract infection and among neonatal factors birth asphyxia, delayed cry and neonatal jaundice to be associated with ASD.[3]
The association between breech presentation and ASD is controversy. We detected in some studies a significant association,[45] while others not found it.[367] So far, only a meta-analysis carried out in the USA by Gardener in 2011. They showed significant relation between breech presentation and ASD among children (odds ratio [OR] = 1.81, 95% confidence interval [CI]: 1.21, 2.71).[8] This meta-analysis has searched databases until 2007, and it limited to four studies. This meta-analysis might lead to the possibility of selection bias. Therefore, the objective of this meta-analysis pooled all of the observational studies to obtain the association between breech presentation and the risk of ASD in children.
METHODS
This meta-analysis was carried out to the assessment of the association between breech presentation and the risk of ASD among children. The PRISMA statement was used as a guide to better-quality reporting of the current review.
Search strategy
A comprehensive literature search of numerous electronic major databases including PubMed, Scopus and Web of science was performed up to 14 May 2018, to find relevant studies. The search was limited to all studies designed case–control and cohort studies in humans with no language restrictions. The reference list of retrieved papers was manually reviewed to identify additional relevant studies that may have been missed during the initial search. The search algorithm was generated as follows: (Autism or ASDs) and (breech presentation or malpresentation).
Inclusion and exclusion criteria
Studies meeting the following inclusion criteria were included: Studies with case–control or cohort study design; and the study population was children diagnosed with autism. Autism diagnostic criteria were International Classification of Diseases (ICD-9), (ICD-10); Diagnostic Statistical Manual of Mental Disorders (DSM-4), (DSM-5); the Autism Diagnostic Observation Schedule and Autism Diagnostic Interview – Revised and records. Exclusion criteria were included: review studies, letters, case reports, conference abstracts and studies which focused on adult autism.
Data extraction and quality assessment
Two independent authors (EJ and SK) performed the initial search, deleted duplicate records, reviewed the title/abstracts and determined as excluded or relevancy. Any disagreement resolved through discussion and consensus between two authors.
A standardised data collection form was built to extract the following information: name of the first author, year of publication, country, study design, number of participants, ASD and breech presentation, diagnostic criteria, sample size, OR and their associated 95% CIs, adjusted or crude reporting of association, child age in diagnose (year) and quality of studies. When multiple publications were from the same population, we only included the latest article.
Quality assessment
We used the improved Newcastle–Ottawa scale to assess the quality of observational studies. The scale consists of three items in reporting of participant's selection, comparability of the autistic and non-autistic children and outcome assessment. Two investigators conducted the quality assessment independently, and scores of the papers were divided into low quality (<7 points) and high quality (≥7 points).
Statistical analysis
All the outcomes were regarded as dichotomous variables; thus, they were expressed as OR with 95% CIs.
Heterogeneity across studies was addressed using the I2 statistic. The low, medium and high heterogeneity was defined by I2 statistic values of 25%, 50% and 75%, respectively.
The publication bias was assessed using the Begg and Egger's regression model and by visually funnel plot asymmetry in included studies. All analyses were performed using Stata software version 13 (Stata Corp, College Station, TX, USA).
RESULTS
Description of studies
A total of 988 studies were included in the initial search. We excluded 186 duplicates and 774 irrelevant articles reviewed by title, abstract and full text. Accordingly, 28 articles were retrieved for further assessment. We excluded 118 articles because they were not original article (i.e., letter, commentary and review) or they did not meet our inclusion criteria. At the end, 10 articles were included in the present analysis. The selection process of studies is shown in Figure 1. The studies were four studies cohort[46910] and six studies case–control[23571112] with sample size 670,063 participants.
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Figure 1: Diagram of studies through the different phases of the systematic review.
The association between breech presentation and ASD among children had the confounder variables including birth year, sociodemographics, parental psychiatric history, maternal age, smoking, the number of previous pregnancies and psychiatric history in maternal.
Main analysis
Figure 2 reports the association between breech presentation and ASD among children. The pooled estimate of OR did not report a significant association between breech presentation and ASD among children (OR = 1.15, 95% CI = 0.93–1.37). There was low heterogeneity among the articles reported risk ASD among children (I2 = 21.0%, P = 0.250).
Figure 2: Forest plot of the association between breech presentation and autism spectrum disorder among children.
Figure 3 presents the association between breech presentation and ASD among children in the unadjusted model. The pooled estimate of OR showed a significant association between breech presentation and ASD among children (OR = 1.32, 95% CI = 1.05–1.58). There was mild heterogeneity among the articles reported the risk of ASD among children in the unadjusted model (I2 = 36.9%, P = 0.124).
Figure 3: Forest plot of the association between breech presentation and autism spectrum disorder among children in the unadjusted model.
No publication bias was detected by the results of Begg's and Egger's tests [Figure 4]. The P value for Begg's and Egger's regression were 0.929 and 0.218, respectively.
Figure 4: Funnel plot of the association between breech presentation and autism spectrum disorder among children.
Quality of the studies
The present meta-analysis had not low-quality according to the NOS Scale [Table 1].
Table 1: Summary results of the included studies
DISCUSSION
The result of the present meta-analysis does not show a significant association between breech presentation and risk of ASD among children according to 10 individual studies in the form of crude and adjusted reported OR. In the present meta-analysis, breech presentation did not increase the risk of ASD among children, but this association was significant in the unadjusted analysis.
Up to date, only a meta-analysis conducted in the USA by Gardener in 2011. They showed a significant relation between breech presentation and ASD among children (OR = 1.81, 95% CI: 1.21, 2.71).[8] This meta-analysis has searched databases until 2007, and it limited to four studies. Furthermore, they did not search Web of Science database. Therefore, this study may lead to the possibility of selection bias.
Risk factors for breech presentation are advanced maternal age, uterine abnormalities, low birth weight, primiparity, prematurity, polyhydramnios, oligohydramnios and congenital anomalies.[4] The association between breech presentation and ASD in the present meta-analysis proposed a shared aetiology instead of a causal relationship. Therefore, this association may be no significant when some confounder's variable is adjusted.
The findings of the present study should be interpreted in light of some limitations. First, differences in using autism criteria and restricted the settings of studies to the good resources countries can affect the generalisability of our findings. Lack of control for some important confounders in included studies can prone findings to confounding effect. However, this meta-analysis is the first to explore strong evidence about the association between breech presentation and the risk of ASD in children with the high sample size among different geographical regions and races.
CONCLUSIONS
The results of this meta-analysis presented that breech presentation was not a risk factor for risk of ASD among children.
Financial support and sponsorship
We thank Hamadan University of Medical Sciences for their financial support in this study.
Conflicts of interest
There are no conflicts of interest.
Acknowledgment
We would like to thank from Hamadan University of Medical Sciences for their financial support in this study.
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