INTRODUCTION
The prevalence of excess body weight (overweight and obesity) has significantly increased worldwide, and a rapid increase has been observed in low- and medium-income countries (1). Currently, more than 50 % of women at reproductive age are overweight, and approximately a 21 % increase in the prevalence rate of obesity may be expected up to 2025 (2,3). In Brazil, 20.7 % of women are obese (4).
The incidence of excess body weight among pregnant women is considered a public health concern due to its serious short- and long-term effects on the health of women and children (5). Excess body weight might affect fertility, conception, embryogenesis, pregnancy, delivery, and post-delivery. Furthermore, maternal obesity might also promote a change in intrauterine environment due to epigenetic factors, causing obesity and its associated morbidities in the offspring (6).
Among the adverse maternal outcomes associated with excess body weight during pregnancy are gestational diabetes mellitus (GDM), hypertensive disorders of pregnancy (HDP), genitourinary tract infections, obstructive sleep apnea, thromboembolic diseases, cholecystitis, depression, higher number of caesarean sections and instrumental deliveries (use of forceps, spatulas, and vacuum extractors), miscarriages, delivery-related complications, and issues associated with breastfeeding (7 8 9-10).
Because of the effects of overweight and obesity on the health of women, the urgency of interventions for the target group, and the growing of obesity rates in Brazil, this study aimed to identify and analysz the publications that showed the effects of pregestational excess weight on pregnancy, delivery, and post-delivery in Brazilian women, which might provide results according to the specificities of our population.
METHOD
This review was conducted from June 2016 to March 2017, and the researchers received assistance from a librarian who specializes in this study design. The recommendations found in the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) Statement (11) were used as tools to guide the elaboration, along with the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) (12). Therefore, considering these criteria, the studies were classified as studies with high (A), moderate (B), low (C), or extremely low (D) evidence grade.
ELIGIBILITY CRITERIA
Observational studies and clinical trials involving pregnant women who presented with adverse outcomes caused by pregestational excess weight, and who lived within the Brazilian territory were eligible for the present study, without restrictions of language or date of publication. Editorials, non-controlled clinical trials, clinical cases, abstracts, pilot studies, systematic reviews, narratives, and deliberative conferences were excluded.
Studies involving teenagers (< 20 years), women who had multiple pregnancies, diseases prior to pregnancy, or pregnancy after bariatric surgery, and women with absence of information regarding nutritional status were excluded. Articles involving women with adverse outcomes who were breastfeeding were excluded from the final step of the study after a re-evaluation of objectives.
Self-reported or measured pregestational body weight and height were used in calculating body mass index (BMI = weight/height in meters2), with cut-off values established according to the criteria that were valid when the studies were conducted. BMI was used to identify pregestational nutritional status (8).
Thus, all adverse outcomes that represented a risk to maternal health were considered, without any previous limitations. A p-value < 0.05 and/or associated measurements with their respective 95 % or 97 % confidence intervals not comprising the value 1 were considered statistically significant.
SOURCES OF INFORMATION AND SEARCH STRATEGIES
Original articles without any restriction in terms of language or date of publication were obtained from the data bases LILACS, MEDLINE via PubMed, Cochrane Library, and Scopus. Additional searches were conducted in the bank of theses and dissertations of Coordination for the Improvement of Higher Education Personnel (Periódicos CAPES).
The descriptors used for the bibliographic search were chosen using the terms in Descritores em Ciências da Saúde (DeCS), in Portuguese, and in Medical Subject Headings (MeSH), in English. Therefore, the following terms were used in the methodology: 'pregnancy', 'gestation', and 'pregnant women' and' overweight', 'obesity', 'body mass index', with their corresponding terms in Portuguese in the context 'Brasil' or 'Brazil', with Boolean operators OR and AND used for word connection.
The controlled vocabulary (MeSH terms) and free terms in the search strategies were defined according to the PECOS system, where population (P) refers to Brazilian adult pregnant women, exposure (E) to overweight and obesity, control (C) to eutrophic adult pregnant women, and results (O) to adverse outcomes or maternal complications, without any restriction of work type (S) in this instance.
The search strategy was properly designed for PubMed, and modified for the other databases; thus, eligible studies were identified (Table I).
ARTICLE SELECTION AND DATA EXTRACTION
The articles were selected based on the previously established criteria for eligibility. The initial selection by title and Abstract was performed independently by two researchers, and non-concordant cases were evaluated by a third researcher. When an article was found in more than one database, only one was considered.
Initially, titles and abstracts were evaluated to assess if they met the pre-defined inclusion criteria. Next, the researchers independently or by pairs reviewed the full articles, and the third reviewer was consulted in case of disagreement.
Data from the articles were then entered in spreadsheets containing the relevant study characteristics important for interpreting the results (study type, follow-up period, control of confusion factors, and adjustments), and analyzed in terms of the quality of evidence as based on the GRADE methodology. The last procedure was conducted independently, with the conflicting cases being evaluated by the third researcher.
RESULTS
The summary of the selection process is shown in the flow diagram (Fig. 1). In total, 39 of 1,582 publications initially screened were selected for final analysis. Of these, 5 (12.8 %), 27 (69.2 %), and 7 (18.0 %) were classified as A, B, and C or D regarding evidence grade, respectively, using the GRADE guideline.
DESCRIPTION OF THE STUDIES INCLUDED
The summary of the general characteristics and qualitative evaluation of the studies is presented in table II. The included studies, all observational in nature, had different sample sizes, objectives and outcomes, were performed between 1991 and 2015, and were published between 2001 and 2016. Most of the investigations focused on the south and south-eastern regions of Brazil (74.4 %).
Table II. Selected studies about the effects of pregestational excess weight on maternal outcomes in Brazilian pregnant women

PGNS: pregestational nutritional status; OW: overweight; OB: obese; WHO: World Health Organization; IOM: Institute of Medicine; BMI: body mass index; PE: pre-eclampsia; GDM: gestational diabetes mellitus; OR: odds ratio; RR: relative risk; CI: confidence interval; HDP: hypertensive disorders of pregnancy; SBP: systolic blood pressure; DBP: diastolic blood pressure; ALI: aminiotic liquid index; GHSP: gestational hypertension superimposed to preeclampsia; CRP: C-reative protein.
About two-thirds of the studies used the recommendations of the World Health Organization (1998), adopted by the Institute of Medicine (2009), for the classification of pregestational nutritional status. Only one article had a distribution of BMI per quartiles. Approximately, 30 % of the studies on excess body weight classified BMI in two independent categories (overweight and obese), and 38.2 % classified it in one category (BMI: ≥ 25 kg/m², ≥ 30 kg/m², or ≥ 35 kg/m²). Studies on maternal outcomes according to class of obesity were not available during the period of data collection.
More than half of the selected studies (51.8 %) reported adverse outcomes associated with excess body weight, including HDP, caesarean section, inadequate weight gain during pregnancy, and GDM. In addition, approximately 48 % of the studies showed an association between pregestational excessive body weight and repeated miscarriages/losses, postpartum weight retention, infections, periodontal disease, metabolic changes, iron deficiencies, behavioural changes, anaesthetic changes, and post-delivery bleeding.
DISCUSSION
The effect of increased BMI on gestation has been widely reported in international studies (52). In addition, there is a dose-response effect with worse outcomes when an increase in obesity class is observed (53). However, in Brazil only few studies focus on this issue due to the difficulty in conducting studies with more representative sample sizes that include pregnant women with excess body weight.
In this review, only results from observational studies were included due to the lack of clinical trials that met the eligibility criteria. Although observational studies are considered as a priori with low quality of evidence, they might assume a better status when methodological criteria are well established and findings are consistent (12). Therefore, some of the studies presented here revealed these conditions.
PREGNANCY-RELATED OUTCOMES
HDP (or increase in blood pressure) and GDM were identified as common clinical findings associated with overweight and obesity (13 14 15 16 17-18, 20, 23, 25, 26, 33, 51). These results are similar worldwide (54). A meta-analysis conducted by Wang et al. (55) revealed that adiposity is an independent risk factor for preeclampsia.
Aiming to quantify the proportion of adverse pregnancy outcomes attributable to maternal obesity, a study conducted in London demonstrated that increased pregestational BMI was independently associated with an increasing risk of diabetes, caesarean section and macrosomia. However, race/ethnicity are potential effect-size modifiers (7).
The current scientific literature has also highlighted the endocrine- metabolic alterations caused by obesity based on the specific markers associated with adverse outcomes in maternal and infant health. Relevant studies were also conducted in Brazil, and some were included in this review (24,27). Although physiological, the change in glucolipid profile when uncontrolled can lead to higher cardiovascular risk, and obesity may have caused such lack of control (56).
Several articles that show the association between pregestational excess weight and accentuated weight gain are available. A systematic review conducted in Brazil by Godoy et al. (57) found a higher incidence of weight gain in Brazilian pregnant women who were overweight. This has been a cause of concern and requires short-term actions and immediate control because these women have a higher risk of developing obesity.
Other outcomes related to excess body weight during pregnancy were identified in this review: a higher occurrence of periodontal disease (19), iron deficiency (21), urinary incontinence (22), sleep disorders (30), sexual dysfunction (29), and changes in body image satisfaction (31,32). It is also relevant that in Brazil a systematic review identified an association between BMI increase during pregnancy and emotional disorders such as depression, anxiety, and stress, caused by humiliation and exposure to obesity-related stigmatization (58).
DELIVERY-RELATED OUTCOMES
Caesarean section among women with excess body weight, particularly when obese, was a common adverse outcome in the present study (40,41,43,49 50- 51, similar to the study by Marchi et al. (32). The biological mechanisms to explain the effect of obesity on this outcome are still not completely elucidated. The increased number of adipocytes in obese individuals may change the pelvic structure, with excessive inflammatory response compromising the physiological process of normal delivery (32).
Increased rates of caesarean section were described in obese women in the presence of fetal distress, cephalopelvic disproportion, and previous caesarean section. On the other hand, the presence of clinical complications such as diabetes and hypertensive disorders is involved in a major proportion of medical referrals for surgical delivery (2). Although these events will add additional risks, overweight and obesity represents an independent risk factor for the occurrence of caesarean section according to a meta-analysis conducted by Chu et al. (59).
Among the studies analyzed, only one cited the induction of labor tha resulted in caesarean section, but does not quantify this occurrence among obese pregnant women. In the study, obese women had a higher rate of cephalopelvic disproportion (11.0 %) as an indication for caesarean section when compared to 6.2 % among eutrophic women (40).
In this sense, national scale studies should be conducted considering the multifactorial network involved in the determination of caesarean section among pregnant women with excess weight. Complications due to anaesthesia, presence of meconium in the amniotic fluid, and increased risk for developing infection are more common in pregnant women with excess body weight (40,42,45). However, these outcomes are yet to be validated. Thus, future studies on this topic must be conducted in Brazil.
POST-DELIVERY-RELATED OUTCOMES
Two studies focusing on the association between maternal excess body weight and maintenance of post-delivery weight were identified (46,48). A systematic review has shown that higher pregestational BMI and accentuated weight gain during pregnancy were strong predictors of obesity among Brazilian women (60).
Despite a lack of studies with more representative samples, the maternal mortality rate is 50 % higher in obese pregnant women, and HDP, which have obesity as risk factor, are considered the primary cause of maternal death in the country. Therefore, the maintenance of normal weight must be reinforced during the start of the reproductive cycle (2,6).
LIMITATIONS
The present review presented some limitations such as the heterogeneity of the studies involved, with different sample sizes and measures of results. Several of the articles showed a variety of outcomes and used different cut-off points for the identification of pregestational excess weight. Some articles considered excess body weight as a single category without distinction between overweight and obesity, and it was not possible to identify studies that described maternal adverse outcomes according to obesity class. This is an important aspect to be considered, since different results could be found by considering obesity BMI classes (53).
Despite these limitations, the study's relevance should be highlighted. There are few studies discussing the association of nutritional status in pregnant women and its effects on maternal outcomes, as the focus has been usually on fetal ones. Our results showed the need for concern about women's health since overweight and obesity are increasing in the Brazilian population, and lead to worse maternal outcomes. If national studies with more robust samples were carried out, we could have an in-depth discussion of this issue in Brazil. All published and available studies on the subject were included in this review, and their results were carefully interpreted.
CONCLUSION
Pregestational excess weight was associated with increasing rates of preeclampsia, gestational hypertension, GDM, excessive gestational weight gain, and caesarean section in Brazilian women.
Despite the lack of studies with more representative samples of Brazilian population, which are strongly recommended, the negative effects of pregestational excess weight reflect the need for effective public policies that may address the problem, focusing on interventions that promote the health of women at reproductive age.