Risk factors for pregnancy-related pelvic girdle pain: a scoping review

Background Pregnancy-related Pelvic Girdle Pain (PPGP) is a common complaint. The aetiology remains unclear and reports on risk factors for PPGP provide conflicting accounts. The aim of this scoping review was to map the body of literature on risk factors for experiencing PPGP. Methods We searched the databases PubMed, Embase, CINAHL, PsycINFO, MIDIRS, and ClinicalTrial.gov (3 August 2020). We selected studies with two reviewers independently. Observational studies assessing risk factors for PPGP were included. Studies examining specific diagnostic tests or interventions were excluded. Results We identified 5090 records from databases and 1077 from ClinicalTrial.gov. Twenty-four records met the inclusion criteria. A total of 148 factors were examined of which only 14 factors were examined in more than one study. Factors that were positively associated with PPGP included a history of low back or pelvic girdle pain, being overweight/obese, already having a child, younger age, lower educational level, no pre-pregnancy exercise, physically demanding work, previous back trauma/disease, progestin-intrauterine device use, stress, depression and anxiety. Conclusions A large number of factors have been examined as potential risk factors for PPGP, but there is a lack of repetition to be able to draw stronger conclusions and pool studies in systematic reviews. Factors that have been examined in more than five studies include age, body mass index, parity and smoking. We suggest a systematic review be conducted to assess the role of these factors further in the development of PPGP. Supplementary Information The online version contains supplementary material available at 10.1186/s12884-020-03442-5.


Background
Pelvic girdle pain has been described as pain experienced between the posterior iliac crest (inferior to L5) and the inferior gluteal folds, particularly near the sacroiliac joints, and pain may radiate in the posterior thigh and can occur in conjunction with or separate from pain in the symphysis [1] (pp797) . Women commonly experience pelvic girdle pain during pregnancy, with reported prevalence of Pregnancy-related Pelvic Girdle Pain (PPGP) ranging from 23 to 65% depending on the study methods used [2][3][4]. Women with PPGP often have impaired mobility, with 7 to 12.5% having to use crutches or a wheelchair [5][6][7]. PPGP symptoms affect their ability to cope with everyday life for which they feel unprepared and which they feel is not acknowledged [8][9][10]. PPGP is also a leading cause of sick leave during pregnancy [11][12][13].
The aetiology of PPGP remains uncertain but hormonal and mechanical factors have been suggested. Regarding hormonal factors, the main focus has been on the hormone relaxin, which is thought to increase pelvic laxity, yet evidence from clinical studies examining the association between relaxin and PPGP is of low quality with inconsistent results [14]. Biomechanically, there is moderate evidence that PPGP is associated with altered motor control, kinetic and kinematic parameters [15]. Knowledge of risk factors for PPGP can guide the development of preventative and management strategies, and can then lead to development of predictive models [16]. Existing narrative reviews, guidelines, background sections of primary studies and patient information vary widely in what they report as risk factors for PPGP and often seem conflicting when compared [1,17,18]. In their paper on the clinical presentation of PPGP, Wu et al. [19] included a structured review on risk factors and interpreted evidence as strong, weak, conflicting, or no evidence based on the number of studies, but numerous studies have been published since then.
The high PPGP prevalence, the increase in published studies on PPGP and the conflicting information in narrative accounts presented a clear need for a scoping review to examine and provide a comprehensive overview of the literature on risk factors for PPGP. A scoping review is a form of knowledge synthesis that maps, summarises and synthesises the evidence on a certain topic [20]. Scoping reviews may also be conducted to determine the value and scope of a full systematic review [21]. Preliminary searches identified a potentially large number of risk factors examined. Hence, a scoping review was perfectly placed for a thorough exploration of the literature to inform future systematic reviews. The aim of this scoping review was thus to map the body of literature on risk factors for experiencing PPGP and to identify research gaps.

Methods
We searched five electronic databases (3 August 2020) including PubMed, Embase, CINAHL, PsycINFO, and MIDIRS with no time filters used. We also searched ClinicalTrial.gov (3 August 2020) for relevant registered studies. Only studies reported in English were included, but no language filter was applied to assess publication bias. We inspected reference lists of included studies and contacted experts in the field. The full search strategy is presented in Additional file 1.
Two review authors (FW, DD) independently reviewed all citations by title and by abstract. Where there was a lack of consensus, citations were moved to full-text selection. Any disagreement at full-text selection was resolved by discussion, and if necessary, involving a third reviewer. The selection criteria are presented in Table 1. Data were extracted independently by FW and DD using a piloted review-specific data extraction sheet. Data extracted included the year and country of publication, study design, setting, inclusion and exclusion criteria, number and characteristics of participants, the exposure and outcome measure(s) and how these were assessed, the number of participants with/without a certain exposure and outcome, and the risk estimates. Consensus was sought and, in addition, 25% of data were rechecked. Findings were summarised narratively and we have provided an overview of all factors examined in the literature in Tables 3, 4, 5 and 6. To map the existing literature on risk factors for PPGP, findings were grouped by trimester of pregnancy (first, second, third or any trimester/trimester not specified), by type of factor (physical, psychological, socio-demographic), and by whether they were examined in more than one study or not.

Results
We identified 5090 records from database searches. After duplicate removal, 3899 records were screened by title, 390 records by abstract, and 261 by full-text, of which 24 records met the inclusion criteria ( Fig. 1). A total of 1077 records were identified from Clinical-Trials.gov one of which was eligible for inclusion but was a duplicate. Studies excluded at full text are listed by reason for exclusion in Additional file 5.
Five of the 24 included studies involved the same cohort, but because different risk factors were examined and reported in the publications, they were all included in the review [25,28,30,31,43]. The characteristics of the 24 included studies are presented in Table 2. Twelve prospective cohort studies, three retrospective studies and nine cross-sectional studies, published between 1995 and 2015 in Norway (n = 13), Sweden (n = 3), Denmark (n = 2), Japan (n = 1), Israel (n = 1), United Kingdom (n = 2), Brazil (n = 1) and Spain (n = 1), were included. All but one study [43] included both nulliparous and multiparous women, and only one study reported results separately for first-time mothers [28]. Eight of the 24 records examined the outcomes of low back pain or lumbopelvic pain during pregnancy in addition to PPGP outcomes, but only PPGP data were included as per review scope. Participants of 20 included studies Table 1 Scope of the scoping review Population Women who were pregnant at any gestation.

Exposure
Any potential risk factor defined as any modifiable or non-modifiable parameter that may increase or decrease the likelihood of a women experiencing PPGP. This excluded specific clinical tests and interventions.

Outcome
Pregnancy-related Pelvic Girdle Pain (PPGP) defined as any pain reported during pregnancy between the posterior iliac crest and the inferior gluteal fold, that may radiate in the posterior thigh and can also occur in conjunction with/or separately in the symphysis [1] Study design Observational prospective and retrospective cohort studies. Crosssectional studies were included if they reported data on any factors that were present prior to the study. Intervention studies, case studies/ reports, reviews, studies that explored overall prognosis, developed prediction models and stratified medicine research [22] were excluded. Only studies published in English were included.
completed self-reported questionnaires, three studies collected data from medical records [39,42,44] and one study conducted structured interviews with women [41]. Three studies also included a physical examination to assess for PPGP [24,29,40]. Seven studies examined the outcome Pelvic Girdle Syndrome (PGS), which is considered a subgroup of PPGP, defined as experiencing pain in the symphysis pubis and both sacro-iliac joints [24,25,28,30,31,36,43]. Seven studies examined pain at the anterior pelvic girdle as outcome, using the terms symphysiolysis [23,41,42], symphysis pubis dysfunction [44,45] or pubis pain [34,46]. Due to these differing inclusion criteria, methods of study, and stages of pregnancy or postpartum, few studies could be identified that would be suitable for meta-analysis in a future systematic review. As these occur, they are noted, and results on all other factors are presented in narrative format.
Risk factors for PPGP examined in more than one study Eleven physical and three socio-demographic potential risk factors were examined in more than one study (Table 3). Findings are also provided in extended tabular format in additional file 2.

Risk factors for PPGP in the second trimester of pregnancy examined in one study
Berg et al. [23] examined two physical potential risk factors for symphysiolysis in the second trimester and found no association with heavy or very heavy physical workload whether this included lifting movements (n = 451; OR 1.3 [0.6-2.5]; p = 0.5) or not (n = 513; OR 1.1 [0.6-2.1]; p = 0.7) ( Table 4).

Risk factors for PPGP in any trimester of pregnancy/ trimester not specified examined in one study
Ten studies examined 48 physical factors, 29 sociodemographic factors, and one psychological factor in relationship to PPGP in any trimester of pregnancy (Table 6). Findings are also provided in extended tabular format in additional file 4.

Discussion
This review represents a comprehensive overview of the available evidence on risk factors for PPGP. A very large number of factors, 148 in total, were examined in 24 studies, yet only 14 factors were examined in more than one study. Definitions of PPGP varied across studies and only three studies included a physical examination despite it being recommended to differentiate PPGP from low back pain [1]. There is an urgent need for consistency in PPGP measurement to allow pooling of data in future systematic reviews. We recommend adhering to the definition of PGP outlined in the European Guidelines and including a physical examination as per the guidelines [1].
Based on the findings of this scoping review, we recommend that systematic reviews are performed on factors that were examined in multiple studies, in particular the factors age, BMI, parity, and smoking, which have been examined in more than five studies. This scoping review can also provide a basis to design robust prospective observational studies to increase Table 6 Risk factor for PPGP in any trimester/trimester not specified examined in only one study (Continued)

Physical factors Socio-demographic factors Psychological factors
Time since last delivery: < 5 years (vs 5 or more) [36] Time since first birth [37] ≥ 4 cups of coffee (per day) [38] Treatment of low back pain by doctor (vs untreated) [40] Treatment of low back pain by chiropractor (vs untreated) [40] Treatment of low back pain by physiotherapist (vs untreated) [40] Untreated low back pain [40] Number of pregnancies [34]  Assessment Use a pain diagram to localise participants' symptoms. If feasible, include a physical examination to identify women with PGP.
If not, recognise this as a limitation. Report the exact questions asked and the full assessment procedure in detail.

Analysis
Conduct descriptive, univariable and multivariable analysis. Adjust for a history of PGP or conduct subgroup analysis by this factor.

Reporting
Fully report the descriptive data (proportion with PGP by the risk factor examined), univariable and multivariable analyses to facilitate pooling of findings in a systematic review.
our understanding of the development of PPGP. Considering the susceptibility of observational research to bias, repetition of studies is required to draw strong conclusions. This is currently lacking for most of the risk factors examined in the literature, making pooling of multiple studies impossible. Issues to consider include the consistency of the association across studies, and, if present, the strength and timing of the association, and the dose-response relation where appropriate. Such research can provide strategies to improve management of this common condition. This is particularly important given the clinical implications of persistent PPGP, which causes new mothers considerable pain and difficulty, sometimes for up to two years postpartum [48,49]. Other concerns in some existing studies that should, where possible, be avoided in future are: small sample sizes, a lack of robust multivariable analysis, and incomplete reporting (of the response rate, assessment procedure, the findings and analysis). Prospective registration of observational studies would also help address some of these issues. Recommendations for future research are summarised in Table 7.

Limitations
We conducted a scoping review of the literature on risk factors for PPGP and thus did not conduct a risk of bias assessment. Ideally, this study will be followed by systematic reviews on specific, potential risk factors that have been examined in more than one study to include a risk of bias assessment before synthesising the literature.

Conclusions
This scoping review presents an overview of current literature on risk factors for PPGP. A total of 148 factors were examined in the included studies, but issues of varying definitions and measurement methods, and a lack of replication were identified, which makes metaanalysis impossible. This review provides a basis to guide future systematic reviews and research on the development of PPGP. In conclusion, the literature on risk factors for PPGP is incomplete and statements regarding such risk factors should reflect current limitations and uncertainty.