https://doi.org/10.14528/snr.2023.57.3.3092 2023. Obzornik zdravstvene nege, 57(3), pp. 175–183. ABSTRACT Introduction: The growing proportion of overweight and obese people worldwide is of great concern as it affects the overall health of people and consequently also their reproductive health. The aim of this literature review is to examine how increased body mass index affects fertility and preconception health in men and women. Methods: A scoping literature review was conducted in February 2021 using PubMed and Medline databases, as well as the Google Scholar search engine. Inclusion criteria consisted of scientific literature, regardless of methodology, and articles published in Slovene and English. Results: The literature search yielded 9 reviews and 5 original quantitative studies published in English in the last 15 years. The results suggest that there is compelling evidence that obese individuals are at increased risk of various health problems in the pre-conception period that may affect their fertility and ability to conceive. Discussion and conclusion: The rising prevalence of high body mass index is changing the reproductive health of men and women. Growing obesity rates, particularly in the Western world, call for greater awareness of this metabolic syndrome and its impact on female and male reproduction. Health professionals working with couples in the pre-conception period should have sufficient knowledge to address the impact of high body mass index on reproductive health and promote a healthy lifestyle. IZVLEČEK Uvod: Naraščajoča stopnja prekomerne telesne mase in debelosti po vsem svetu ovira zdravje moških in žensk ter posledično vpliva na njihovo reproduktivno zdravje. Namen tega pregleda literature je raziskati, kako povečan indeks telesne mase vpliva na plodnost in zdravje moških in žensk pred spočetjem. Metode: Opravljen je bil pregled literature. Iskanje literature je potekalo februarja 2021 v podatkovnih bazah PubMed in Medline. Drugi iskalni zadetki so bili najdeni s pomočjo Google Učenjaka. Vključitveni kriteriji so zajemali znanstveno literaturo, ne glede na metodološki pristop, v slovenskem in angleškem jeziku. Rezultati: V pregled literature je bilo vključenih devet preglednih in pet izvirnih člankov kvantitativne metodologije. Ugotovitve raziskav kažejo, da imajo posamezniki s povišano telesno težo v predkoncepcijskem obdobju večje tveganje za številne zdravstvene težave, ki lahko vplivajo na njihovo plodnost in sposobnost zanositve. Diskusija in zaključek: Povišanje indeksa telesne mase vpliva na reproduktivno zdravje moških in žensk. Naraščajoča stopnja debelosti predvsem v zahodnem svetu zahteva večjo ozaveščenost o tem presnovnem sindromu in njegovem vplivu na reprodukcijo žensk in moških. Zdravstveni delavci, ki delajo s pari s prekomerno telesno maso v obdobju pred spočetjem, morajo imeti ustrezno znanje za njihovo obravnavo ter spodbujati zdrav način življenja. Key words: increased body weight; preconception period; family planning; fertility; health promotion Ključne besede: povišana telesna teža; prednosečnostno obdobje; načrtovanje družine; plodnost; promocija zdravja 1 University of Ljubljana, Faculty of Health Sciences, Department of Midwifery, Zdravstvena pot 5, 1000 Ljubljana, Slovenia 2 University of Primorska, Faculty of Health Sciences, Department of Nursing, Polje 42, 6310 Izola, Slovenia * Corresponding author/ Korespondenčni avtor: petra.petrocnik@zf.uni-lj.si Review article/Pregledni znanstveni članek The effects of increased body mass index on preconception health: A scoping literature review Vpliv povišanega indeksa telesne mase na predkoncepcijsko zdravje: pregled literature Petra Petročnik1,*, Mirko Prosen2, Ana Polona Mivšek1 Received/Prejeto: 21. 11. 2022 Accepted/Sprejeto: 19. 3. 2023 © 2023 Avtorji/The Authors. Izdaja Zbornica zdravstvene in babiške nege Slovenije - Zveza strokovnih društev medicinskih sester, babic in zdravstvenih tehnikov Slovenije./Published by Nurses and Midwives Association of Slovenia. To je članek z odprtim dostopom z licenco CC BY-NC-ND 4.0./This is an open access article under the CC BY-NC-ND 4.0 license. 176Petročnik et al. (2023)/Obzornik zdravstvene nege, 57(3), pp. 175–183. Introduction The global population is experiencing increased levels of overweight and obesity. This was first observed in Western countries, but now also affects other middle- and low-income countries (World Health Organization [WHO], 2021). Slovenia is no exception. It is estimated that in 2016, 1.9 billion adults were overweight and 650 million of them were obese (WHO, 2021). The Centers for Disease Control and Prevention (CDC, 2022) reported that in the last 20 years the prevalence of obesity in the United Stated has increased by over 10% (CDC, 2022). Rising levels of body mass index (BMI) are strongly associated with multiple risk factors that affect health, such as heart disease, stroke, type 2 diabetes and certain forms of cancer (CDC, 2022; Imterat, Agarwal, Esteves, Meyer, & Harlev, 2019; Stephenson et al., 2018). As obesity is becoming a major global health problem, many risk factors associated with an elevated BMI also affect pregnant women, childbirth and/or the foetus/baby and should therefore be addressed before pregnancy. According to the Healthy Eating Index (HEI) (Tsigga, Filis, Hatzopoulou, Kotzamanidis, & Grammatikopoulou 2011), this could be due to the fact that women with a higher pre-pregnancy BMI have poorer diet quality during pregnancy. On the other hand, pregnancy is also the time when women are highly motivated to make healthy dietary and lifestyle changes (Lindqvist, Lindkvist, Eurenius, Persson, & Mogren, 2017), and it should therefore be used to promote healthy habits. The nutritional status of adults can be measured with a predictive calculation tool, namely the body mass index (BMI). Although the calculation of BMI varies from country to country, in Slovenia it is calculated by dividing the person's weight (in kilograms) by the square of their height (in metres). According to the World Health Organization (WHO, 2019), it can be used for adults over 20 years of age and is divided into the categories listed in Table 1. Obesity in pregnancy increases the risk of various health complications, such as gestational hypertension, pre-eclampsia, and gestational diabetes (Poston, Harthoorn, & van der Beek, 2011). It also elevates the risk of induction of labour and prolonged labour (NICE, 2023), Caesarean section, postpartum haemorrhage, postpartum infections, and preterm birth (Creanga, Catalano, & Bateman, 2022). Obese women are more likely to suffer from depression and anxiety during pregnancy and after delivery (Dachew, Ayano, Betts, & Alati, 2021). In addition, as babies born to obese mothers are more likely to suffer from congenital anomalies, obesity affects the developing foetus and newborn. They often have macrosomia or are large for gestational age, which can lead to shoulder dystocia and other labour complications and potential morbidities for both mother and baby (Creanga, Catalano, & Bateman, 2022). As far as we know, many studies and textbooks address the effects of obesity on pregnancy, delivery and the postpartum period. However, not much attention has been paid to maintaining a healthy body weight before planning pregnancy. Aims and objectives The aim of this literature review was to investigate how increased BMI affects preconception health and fertility in men and women. Methods A scoping review was conducted. According to Munn et al. (2018), scoping reviews present a relatively new form of literature review and should be used when identifying or discussing specific concepts and characteristics of articles or studies. Review methods The literature was searched in PubMed and Medline databases in February 2021. The search strategy also included a search in Google Scholar. We searched for articles published in Slovene and English in the last fifteen years using the following search terms including Boolean operators: (BMI OR body mass index OR overweight OR obese) AND (preconception OR fertility) AND (health OR effect on health). Results of the review Our search results were screened using the Prisma flow diagram (Page et al., 2020), which initially yielded 2,252 records. In the first step of study identification and selection (Figure 1), duplicates and ineligible studies were excluded, resulting in 536 studies. All remaining studies were screened by title and aim. In total, 38 studies were eligible for full-text screening against the inclusion and exclusion criteria. Of these, 14 studies were selected and included in this review. Table 1: Body mass index classification (WHO, 2019) Tabela 1: Klasifikacija indeksa telesne mase (WHO, 2019) BMI/ ITM Nutritional status/ Prehranski status Below 18.5 Underweight 18.5–24.9 Normal weight 25.0–29.9 Pre-obesity 30.0–34.9 Obesity class I 35.0–39.9 Obesity class II Above 40 Obesity class III Legend/Legenda: BMI – body mass index / indeks telesne mase 177 Petročnik et al. (2023)/Obzornik zdravstvene nege, 57(3), pp. 175–183. Quality assessment of the review and description of data processing Articles included in this review were published in peer-reviewed international journals and quality assessed using the Critical Appraisal Skills Programme (CASP) instrument (CASP, 2020). Review articles were screened using the CASP systematic review checklist, and other studies were screened using the CASP cohort study checklist. All studies included in this review were considered eligible. As this was a scoping review that included different types of study design, the results are reported thematically. Results Our literature search identified 9 review articles and 5 original research articles, the main characteristics of which are presented in Table 3. Results were extracted for overweight and obese women and men. The combination of an unhealthy diet and an increasingly sedentary lifestyle in the Western world has led to a growing number of obese people, which also applies to women and men in the preconception period (Du Plessis, Cabler, McAlister, Sabanegh, & Agarwal, 2010; Çekici, 2018). Figure 1: PRISMA flow chart diagram (Page et al.,2020) Slika 1: PRISMA diagram poteka (Page et al.,2020) Records identified from: Databases (n = 2236) Other sources (n = 16) Records excluded before screening: Duplicate records and ineligible studies excluded (n = 1716) Records screened (n = 536) Records excluded based on the study aim/purpose (n = 498) Reports sought for retrieval (n = 38) Reports not retrieved (n = 0) Reports assessed for eligibility (n = 38) Reports excluded: For not meeting the inclusion and exclusion criteria (n = 24) Studies included in the review (n = 14) Identification of studies via databases and registers Id en tif ic at io n Sc re en in g In cl ud ed 178Petročnik et al. (2023)/Obzornik zdravstvene nege, 57(3), pp. 175–183. Table 2: Inclusion and exclusion criteria Tabela 2: Vključitveni in izključitveni kriteriji Inclusion criteria/Vključitveni kriteriji Exclusion criteria/Izključitveni kriteriji Type of studies: original and review articles / Studies published between 2006 and 2020 Studies published before 2006 Scientific articles Other professional articles Language of publication: English, Slovene Other languages Studies investigating or reviewing the impact of increased BMI on preconception health Studies investigating the impact of BMI on other periods of reproductive age. Table 3: Characteristics of studies included in the review Tabela 3: Značilnosti študij vključenih v pregled literature Authors, year, country/ Avtorji, leto, država Research design/ Raziskovalni dizajn Aim/ Namen Main results/ Glavni rezultati Anifandis, Dafopoulos., Messini, Polyzos, & Messinis, 2013 Greece Retrospective study, quantitative design The primary aim of this study was to investigate the correlation between men's BMI and their sperm parameters (volume, concentration and motility) and to determine whether or not it affects embryo quality and IVF outcome. Its secondary aim was to investigate the influence of BMI of both men and women in combination with their age on IVF outcomes. The overall (n = 301) BMI and age of men did not correlate with their sperm parameters. Group 1 and group 4 had the highest embryo quality and consequently the highest percentage of pregnancies regardless of the BMI of their partners. The BMI of men did not correlate with their sperm parameters, but did affect the quality of the embryos produced in a way that influenced the pregnancy rate. Çekici, 2018 Turkey Literature review To outline various dietary factors affecting fertility or infertility in women and men. The review article presents various dietary intakes affecting fertility or infertility in men and women. Chambers & Anderson, 2015 UK Literature review To examine the factors of obesity that have an impact on male fertility. It is important to emphasise that fertility is a complex, multifactorial process. Obesity affects male fertility through several mechanisms, including obesity-associated hypogonadism, its effects on sperm production and function, and its atherogenic effects on the peripheral vasculature, which may also cause erectile dysfunction. The article discusses the transgenerational impact of paternal obesity. Du Plessis et al., 2010 South Africa & USA Literature review To present the effect of obesity on sperm disorders and male infertility, and provide an overview of the potential mechanisms and possible treatment options. Population-based studies conducted over the past 5–10 years have indicated an increased likelihood of abnormal sperm parameters in overweight and obese men, and a potentially increased likelihood of subfertility in couples with an obese male partner. Additional characteristics associated with male obesity that could contribute to an increased risk of infertility include altered retention and metabolism of environmental toxins, unhealthy lifestyle factors and sexual dysfunction. Hajshafiha, Ghareaghaji, Salemi, Sadegh-Asadi, & Sadeghi- Bazargani, 2013 Iran & Sweden Clinical study, quantitative approach The aim of this study was to investigate the role of BMI on certain laboratory indicators of male fertility in infertile and fertile men in an Iranian population. The studied correlation between BMI and certain sex hormones and sperm characteristics, as well as the different patterns of this correlation between fertile and subfertile/infertile men, will contribute to our understanding of the impact of obesity on certain physiological characteristics of male reproduction in fertile and infertile men. Continues/Se nadaljuje 179 Petročnik et al. (2023)/Obzornik zdravstvene nege, 57(3), pp. 175–183. Authors, year, country/ Avtorji, leto, država Research design/ Raziskovalni dizajn Aim/ Namen Main results/ Glavni rezultati Imterat, Esteves, Meyer, Harlev, & Agarwal, 2019 Israel, Brazil & USA Literature review The aim of this study was to review information on the effects of BMI on female fertility and the outcomes of assisted reproductive technology (ART). Imbalances along the hypothalamus- pituitary-ovarian axis may hinder couples' efforts to conceive. BMI and reproductive physiology are regulated by leptin and oestrogen. Lifestyle changes before and during have a positive impact on fertility. Kort et al., 2006 USA Clinical study, quantitative approach The aim of the study was to determine the relationship between BMI and sperm parameters, including its chromatin integrity. Men whose BMI is higher than 25 kg/m2 have fewer chromatin-intact normal-motile sperm cells per ejaculate. Patients may thus be advised to reduce their body weight so as to ensure maximum fertility potential. Lash & Armstrong, 2009 USA Literature review The aim of the study was to review the effects of obesity on women's reproductive health and fertility. Obesity is associated with early puberty, irregular menstrual patterns, reduced contraceptive effectiveness, ovulatory disorders, higher rates of miscarriage, and poorer outcomes of assisted reproductive technology. Many of these problems can be alleviated through weight loss. Palmer, Bakos, Fullston, & Lane, 2012 Australia Literature review This review study focuses on the impact of male obesity on fertility and sperm quality, focusing on the proposed mechanisms and potential reversibility of these negative effects. Over the last 30 years, obesity among men of reproductive age has almost tripled, coinciding with a global escalation in male infertility. Recent studies show that male obesity reduces sperm quality, and more importantly, alters the physical and molecular structure of germ cells in the testes and mature sperm, negatively impacting male reproductive potential. Obesity in men has also been shown to affect the metabolic and reproductive health of offspring, suggesting that paternal health traits are passed on to the next generation with the mediator likely being sperm. Pandey, Pandey, Maheshwari, & Bhattacharya, 2010 UK Literature review To examine the effects of obesity on fertility and fertility treatment outcomes. Obesity in women has implications for fertility and fertility treatment. A higher BMI lowers the likelihood of conception in ovulating women and negatively affects the results of ovulation induction treatments. Obese women undergoing IVF treatment require higher doses of gonadotropins, have less success in ovarian stimulation and fewer oocytes are harvested. Obesity is also associated with lower fertilisation rates, poorer quality embryos and a higher likelihood of miscarriage. While weight loss does improve women's reproductive outcomes, it must be gradual and consistent in order to be effective. Sallmén, Sandler, Hoppin, Blair, & Baird, 2006 Finland Retrospective study, quantitative approach To investigate the association between male BMI and couple infertility in men participating in the Agricultural Health Study, a study conducted on male pesticide applicators and their partners. Restriction of data to couples with the highest-quality infertility data showed a dose-response correlation, as well as a stronger effect of BMI. The correlation between BMI and infertility was similar in older and younger men, indicating that erectile dysfunction in older men does not account for the correlation. Continues/Se nadaljuje 180Petročnik et al. (2023)/Obzornik zdravstvene nege, 57(3), pp. 175–183. Overweight and obesity in women Overweight and obesity may lead to several problems that affect preconception health and possibly women's ability to conceive. These include changes in the menstrual cycle, reduced effectiveness of contraceptive methods, reduced fertility, and reduced effectiveness of fertility treatments and assisted reproduction. The pathophysiology of obesity leads to changes in metabolic and hormonal factors influencing obesity phenotypes (Zain & Norman, 2008). In obese girls, puberty usually begins at an earlier age. Girls who experience earlier sexual development may have psychosocial problems. In the physical sense, hormonal imbalances caused by obesity may disrupt the menstrual cycle and manifest in dysfunctional uterine bleeding (Lash & Armstrong, 2009; Souter, Baltagi, Kuleta, Meeker, & Petrozza, 2011). In addition, steroid contraceptive methods such as oral contraceptive pills and progestin-only pills have been shown to be less effective in obese women. This reduced effectiveness of steroid contraceptives is mainly due to changes in steroid metabolism and distribution in obese women. As obese women are also at increased risk of thrombosis, they should be warned that this risk is even greater when taking oral contraceptives (Lash & Armstrong, 2009). Studies show that, due to anovulation and subfecundity, obesity reduces fertility rates and prolongs the time to conception (Imterat et al., 2019; Lash & Armstrong, 2009; Pandey, Pandey, Maheshwari, & Bhattacharya, 2010). As obese women are often hyper-insulinemic, they are at increased risk for an endocrine profile characteristic of polycystic ovarian syndrome (PCOS) (Imterat et al., 2019; Lash & Armstrong, 2009; Zain & Norman, 2008). PCOS is a heterogeneous condition characterised by alteration of the menstrual cycle, oligo- or anovulation and even hyperandrogenism (Pandey et al., 2010; Moussa, Alrais, Leon, Abbas, & Sibai, 2016). Obese women also face increased rates of infertility due to anovulation and hormonal changes alone (Imterat et al., 2019; Lash & Armstrong, 2009). Imterat et al. (2019) reported that obese women were found to have lower oocyte quality compared to normal weight women. A high BMI also affects the ability to conceive using assisted reproduction techniques (ART). The higher a woman's BMI, the lower her chance of conceiving with ART (Lash & Armstrong, 2009). Women struggling with obesity and seeking fertility treatment should seriously consider weight loss, as this has a positive impact on ART techniques (Lash & Armstrong, 2009). Overweight and obesity in men Evidence suggests that male obesity also has a negative effect on the reproductive process. In addition, increased BMI in the male partner has been shown to prolong the time to conception, even when the female partner's BMI is within the normal range (Palmer, Bakos, Fullston, & Lane, 2012). Obesity in men is strongly associated with hypogonadism (Chambers & Anderson, 2015) and infertility (Sallmen et al., 2006). This is partly due to reduced sperm quality and sperm concentration, as well as altered physical and molecular structure of germ cells in the testes and Authors, year, country/ Avtorji, leto, država Research design/ Raziskovalni dizajn Aim/ Namen Main results/ Glavni rezultati Moussa, Alrais, Leon, & Abbas, Sibai, 2016 USA Literature review This literature review examines the impact of obesity on lives of women, describing complications from preconception to the postpartum period. Increased BMI is correlated with poorer perinatal outcomes, including increased rates of gestational diabetes, pre-eclampsia (and other hypertension disorders), macrosomia, and neonatal morbidities. Isolated maternal obesity and maternal diabetes predispose the infant to potential diseases in adulthood through foetal programming. Souter, Baltagi, Kuleta, Meeker, & Petrozza, 2011 USA Retrospective study To examine the fertility of overweight and obese infertile women undergoing gonadotropins treatment and intrauterine insemination (IUI). While women with obesity need higher doses of medication and produce fewer follicles per dose, after adjustment for medication and response to overcome the weight effect, the success of the treatment cycle is comparable to that of normal weight women. Zain & Norman, 2008 Australia & Malaysia Literature review To examine the impact of obesity on female fertility and fertility treatments. This review article presents various factors of obesity that affect female fertility and fertility treatments. Legend/Legenda: n – number/število; BMI – body mass index/indeks telesne mase; kg – kilogram/kilogram; m2 – square meter/ kvadratni meter; ART – assisted reproductive technology/asistirane reproduktivne tehnike; IVF – in vitro fertilization/in vitro fertilizacija; USA – United States of America/Združene države Amerike; UK – United Kingdom/Združeno Kraljevstvo 181 Petročnik et al. (2023)/Obzornik zdravstvene nege, 57(3), pp. 175–183. later mature sperm (Du Plessis et al., 2010; Hajshafiha, Ghareaghaji, Salemi, Sadegh-Asadi, & Sadeghi- Bazargani, 2013; Kort et al., 2006; Palmer et al., 2012). The altered hypothalamic-pituitary-gonadal axis in obesity deregulates the process of spermatogenesis itself. Obese men experience hormonal imbalances due to the elevated levels of white adipose tissue, which causes increased conversion of androgen hormones to oestrogens. Another hormone produced by white adipose tissue is leptin, which plays an important role in regulating energy intake. In simple terms, the increased production of leptin significantly reduces the production of testosterone. Moreover, due to adiposity of scrotal tissue, obese men experience increased temperature in the gonads, which affects the process of spermatogenesis, which is very sensitive to increased heat (Chambers & Anderson, 2015; Du Plessis et al., 2010; Palmer et al., 2012). Research also shows that increased male BMI affects the quality of embryos produced during in vitro fertilisation (IVF), resulting in lower pregnancy rates (Anifandis et al., 2013). Discussion Although preconception care has been largely neglected in the past, there is a growing body of research stressing the importance of a healthy lifestyle in the preconception period (Stephenson et al., 2018). Not only can this influence an individual's future reproduction, but it can also have consequences that may affect future generations (Stephenson et al., 2018). This scoping review provides evidence from several studies highlighting multiple negative effects of increased BMI for women and men in the preconception period. Overweight or obese women often experience changes in their menstrual cycle (Souter et al., 2011). Obese girls are more prone to early puberty (Souter et al., 2011), and earlier sexual development may in turn lead to psychosocial distress. Given the increasing number of overweight and obese children (WHO, 2021), it is reasonable to assume that menarche and other signs of puberty will continue to occur earlier. Changes in the menstrual cycle (Lash & Armstrong, 2009; Souter et al., 2011), combined with reduced fertility rates due to anovulation, subfecundity and spontaneous abortion (Imterat et al., 2019; Lash & Armstrong, 2009), reduce women's chances of becoming pregnant. In view of increasing obesity among women, the number of infertile or subfertile women is expected to continue to rise. In the context of family planning methods, particular attention needs to be paid to obese women, as contraceptives are less effective for this group (Lash & Armstrong, 2009). It must be emphasised that increased BMI also affects men's reproductive health, leading to negative consequences such as hypogonadism (Chambers & Anderson, 2015) and infertility (Sallmen et al., 2006) due to lower sperm quality (Du Plessis et al., 2010; Hajshafiha et al., 2013; Palmer et al., 2012), changes in spermatogenesis, hormonal imbalance and increased heat in the gonads (Chambers & Anderson, 2015; Du Plessis et al., 2010; Palmer et al., 2012). It should not be underestimated that male obesity has negative effects on the metabolic and reproductive health of offspring (Chambers & Anderson, 2015; Palmer et al., 2012). This has been confirmed by the Lancet series which shows that the preconception nutritional status of parents can have a negative impact on the risk of future children for cardiovascular, immunological, neurological and metabolic morbidity (Barker et al., 2018; Fleming et al., 2018). This scoping literature review sheds light on the importance of recognising the impact of increased body weight on preconception and subsequent health. This review could be structured in a more systematic manner. In terms of public health awareness, there is a need for a greater focus on the preconception period to improve the future health of mothers, fathers and their children. In the past, the preconception period has been of interest for family planning only in terms of preventing unwanted pregnancies and sexually transmitted infections. However, given the alarming trend of declining fertility rates among men and women around the world, we need to raise awareness and address the question of how to preserve the fertility of the population without delay. Health professionals, especially midwives and nurses, should emphasise the importance of the preconception health in a broader context to support preventive efforts related to maintaining a healthy body weight in the population. As suggested by Bizjak, Peršolja, & Zadnik Stirn (2016), nutrition counselling should be established at the primary care level, where individuals can access nutritional treatment. Conclusion It is evident that increased BMI levels have both short and long-term consequences for health, including in the preconception period. For this reason, health professionals should encourage both the young and adult population to maintain a healthy body weight. They should also provide appropriate methods for counselling overweight or obese individuals. Preventive programmes promoting the maintenance of normal body weight should focus on healthy lifestyle habits, including healthy nutrition and regular physical activity. It is crucial that health professionals advocate for a healthy lifestyle and address the negative consequences of obesity, also in terms of future reproduction. Further research should focus on the factors associated with the effects of increased BMI on pregnancy, childbirth and the newborn baby. 182Petročnik et al. (2023)/Obzornik zdravstvene nege, 57(3), pp. 175–183. Conflict of interest/Nasprotje interesov The authors declare no conflict of interest./Avtorji izjavljajo, da ni nasprotja interesov. Funding/Financiranje The study was co-funded by the Erasmus plus KA2 programme of the European Union, under the project entitled »Preconception health of youth, bridging the gap in and through education (PreconNet).«/ Raziskava je bila sofinanciran na podlagi programa Erasmus plus KA2 Evropske Unije, v okviru projekta z naslovom »Preconception health of youth, bridging the gap in and through education (PreconNet).« Ethical approval/Etika raziskovanja This review was prepared in accordance with the Helsinki-Tokyo declaration (World Medical Association, 2013) and the Code of Ethics for Midwives in Slovenia (2014)./Pregled literature je bil pripravljen v skladu z načeli Helsinško-tokijske deklaracije (World Medical Association, 2013) in Kodeksa etike za babice Slovenije (2014). Author contributions/Prispevek avtorjev The first author conceptualised the study and conducted the literature search. The second and third authors reported on the results and interpreted them in the discussion section./Prva avtorica je zasnovala pregled literature in opravila iskanje literature. K temu sta se pridružila drugi avtor oziroma tretja avtorica, ki sta sodelovala pri poročanju rezultatov in v diskusiji. Literature Anifandis, G., Dafopoulos, K., Messini, C. I., Polyzos, N., & Messinis, I. E. (2013). The BMI of men and not sperm parameters impact on embryo quality and the IVF outcome. Andrology, 1(1), 85–89. https://doi.org/10.1111/j.2047-2927.2012.00012.x PMid:23258634 Barker, M., Dombrowski, S. U., Colbourn, T., Fall, C., Kriznik, N. M., Lawrence, W. T., Norris, S. A. … Stephenson, J. (2018). Intervention strategies to improve nutrition and health behaviours before conception. Lancet, 391(10132), 1853–1864. https://doi.org/10.1016/S0140-6736(18)30313-1 PMid:29673875 Bizjak, M., Peršolja, M., & Zadnik Stirn, L. (2016). Mnenje strokovnjakov o uporabi celostnega prehranskega protokola v praksi pri preprečevanju debelosti. Obzornik Zdravstvene Nege, 50(3), 224–231. https://doi.org/10.14528/snr.2016.50.3.97 Centers for Disease Control and Prevention (CDC). (2022). Adult obesity facts. Retrieved September 13, 2022 from https:// www.cdc.gov/obesity/data/adult.html Critical Appraisal Skills Programme (CASP). (2020). CASP checklist. Retrieved October 20, 2022 from https://casp-uk.net/ casp-tools-checklists/ Çekici, H. (2018). Current nutritional factors affecting fertility and infertility. Annals of Clinical and Laboratory Research, 6(1), 225. https://doi.org/10.21767/2386-5180.1000225 Chambers, T. J. G., & Anderson, R. A. (2015). The impact of obesity on male fertility. Hormones, 14(4) 563–568. https://doi.org/10.14310/horm.2002.1621 PMid:26732149 Creanga, A. A., Catalano, P. M., & Bateman, B. T. (2022). Obesity in pregnancy. The New England Journal of Medicine, 387(3), 248–259. https://doi.org/10.1056/NEJMra1801040 PMid:35857661 Dachew, B.A., Ayano, G., Betts, K., & Alati, R. (2021). The impact of pre-pregnancy BMI on maternal depressive and anxiety symptoms during pregnancy and the postpartum period: A systematic review and meta-analysis. Journal of Affective Disorders, 281, 321–330. https://doi.org/10.1016/j.jad.2020.12.010 PMid:33341015 Du Plessis, S. S., Cabler, S., McAlister, D. A., Sabanegh, E., & Agarwal, A. (2010). The effect of obesity on sperm disorders and male infertility. Nature reviews. Urology, 7(3), 153–161. https://doi.org/10.1038/nrurol.2010.6 PMid:20157305 Fleming, T. P., Watkins, A. J., Velazquez, M. A., Mathers, J. C., Prentice, A. M., Stephenson, J. … Godfrey, K. M. (2018). Origins of lifetime health around the time of conception: Causes and consequences. Lancet, 391(10132), 1842–1852. https://doi.org/10.1016/S0140-6736(18)30312-X PMid:29673874 Hajshafiha, M., Ghareaghaji, R., Salemi, S., Sadegh-Asadi, N., & Sadeghi-Bazargani, H. (2013). Association of body mass index with some fertility markers among male partners of infertile couples. International Journal of General Medicine, 6, 447–451. https://doi.org/10.2147/IJGM.S41341 PMid:23785240; PMCid:PMC3682849 Imterat, M., Agarwal, A., Esteves, S. C., Meyer, J., & Harlev, A. (2019). Impact of body mass index on female fertility and ART outcomes. Panminerva Medica, 61(1), 58–67. https://doi.org/10.23736/S0031-0808.18.03490-0 PMid:29962181 183 Petročnik et al. (2023)/Obzornik zdravstvene nege, 57(3), pp. 175–183. Kort, H. I., Massey, J. B., Elsner, C. W., Mitchell-Leef, D., Shapiro, D. B., Witt, M. A., & Roudebush, W. E. (2006). Impact of body mass index values on sperm quantity and quality. Journal of Andrology, 27(3), 450–452. https://doi.org/10.2164/jandrol.05124 PMid:16339454 Lash, M. M., & Armstrong, A. (2009). Impact of obesity on women's health. Fertility and Sterility, 91(5), 1712–1716. https://doi.org/10.1016/j.fertnstert.2008.02.141 PMid:18410940 Lindqvist, M., Lindkvist, M., Eurenius, E., Persson, M., & Mogren, I. (2017). Change of lifestyle habits: Motivation and ability reported by pregnant women in northern Sweden. Sexual & Reproductive Healthcare, 13, 83–90. https://doi.org/10.1016/j.srhc.2017.07.001 PMid:28844363 Moussa, H. N., Alrais, M. A., Leon, M. G., Abbas, E. L., & Sibai, B. M. (2016). Obesity epidemic: Impact from preconception to postpartum. Future science OA, 2(3), Article FSO137. https://doi.org/10.4155/fsoa-2016-0035 PMid:28031980; PMCid:PMC5137925 Munn, Z., Peters, M., Stern, C., Tufanaru, C., McArthur, A., & Aromataris, E. (2018). Systematic review or scoping review: Guidance for authors when choosing between a systematic or scoping review approach. BMC Medical Research Methodology, 18(1), 143. https://doi.org/10.1186/s12874-018-0611-x PMid:30453902; PMCid:PMC6245623 National Institute for Health and Care Excellence Excellence [NICE]. (2023). Weight management before, during and after pregnancy: Public Health Guideline. Retrieved February 27, 2023 from https://www.nice.org.uk/guidance/ph27/resources/ weight-management-before-during-and-after-pregnancy- pdf-1996242046405. Palmer, N. O., Bakos, H. W., Fullston, T., & Lane, M. (2012). Impact of obesity on male fertility, sperm function and molecular composition. Spermatogenesis, 2(4), 253–263. https://doi.org/10.4161/spmg.21362 PMid:23248766; PMCid:PMC3521747 Pandey, S., Pandey, S., Maheshwari, A., & Bhattacharya, S. (2010). The impact of female obesity on the outcome of fertility treatment. Journal of Human Reproductive Sciences, 3(2), 62–67. https://doi.org/10.4103/0974-1208.69332 PMid:21209748; PMCid:PMC2970793 Sallmén, M., Sandler, D. P., Hoppin, J. A., Blair, A., & Baird, D. D. (2006). Reduced fertility among overweight and obese men. Epidemiology, 17(5), 520–523. https://doi.org/10.1097/01.ede.0000229953.76862.e5 PMid:16837825 Souter, I., Baltagi, L. M., Kuleta, D., Meeker, J. D., & Petrozza, J. C. (2011). Women, weight, and fertility: The effect of body mass index on the outcome of superovulation/intrauterine insemination cycles. Fertility and Sterility, 95(3), 1042–1047. https://doi.org/10.1016/j.fertnstert.2010.11.062 PMid:21195401 Stephenson, J., Heslehurst, N., Hall, J., Schoenaker, D., Hutchinson, J., Cade, J. E. … Mishra, G. D. (2018). Before the beginning: Nutrition and lifestyle in the preconception period and its importance for future health. Lancet, 391(10132), 1830–1841. https://doi.org/10.1016/S0140-6736(18)30311-8 PMid:29673873 Tsigga, M., Filis, V., Hatzopoulou, K., Kotzamanidis, C., & Grammatikopoulou, M. G. (2011). Healthy Eating Index during pregnancy according to pre-gravid and gravid weight status. Public Health Nutrition, 14(2), 290–296. https://doi.org/10.1017/S1368980010001989 PMid:20642871 World Health Organization (WHO). (2019). Body mass index – BMI. Retrieved October 29, 2022 from http://www.euro.who. int/en/health-topics/disease-prevention/nutrition/a-healthy- lifestyle/body-mass-index-bmi World Health Organization (WHO). (2021). Obesity and overweight. Retrieved October 29, 2022 from https://www. who.int/news-room/fact-sheets/detail/obesity-and-overweight Zain, M. M., & Norman, R. J. (2008). Impact of obesity on female fertility and fertility treatment. Women's Health, 4(2), 183–194. https://doi.org/10.2217/17455057.4.2.183 PMid:19072520 Cite as/Citirajte kot: Petročnik, P., Prosen, M., & Mivšek, A. P. (2023). The effects of increased body mass index on preconception health: A scoping literature review. Obzornik zdravstvene nege, 57(3), 175–183. https://doi.org/10.14528/snr.2023.57.3.3092