1. Introduction
Primary infertility is the inability to conceive a pregnancy despite living with partner and having unprotected intercourse for 12 months or more in people aged 15-49 years [1]. Some of the major causes of primary infertility are environmental toxins, smoking, obesity, and psychological stress [3]. Women with high body mass index (BMI) are at risk of polycystic ovary syndrome and infertility [8]. However, the association of obesity and physical activity with fertility is not well clear and needs further study [18]. There are conflicting results about the effects of the type, intensity and frequency of physical activity on infertility in pregnant women [19]. In some cases, the destructive effect of high intensity activity on the relative reduction of infertility and ovulation has been suggested [20], but some researchers have found no association between the patterns of physical activity and infertility [12, 16]. Considering the critical effects of lifestyle on reproductive health, this study aims to compare the physical activity and body composition of fertile and infertile women.
2. Materials and Methods 
This is a case-control study that was performed on 100 fertile and 100 infertile women aged 20-40 years referred to three infertility treatment centers in Arak, Iran. The  treatment centers were selected using a convenience sampling method, of which samples were randomly selected. In order to select the control group, multi-stage sampling method was used; the city of Arak was divided into three regions based on their socio-economic status. Of each region, a health center was randomly selected and 100 people were randomly selected from them. 
To assess the level of physical activity in women, the short form of the International physical activity questionnaire (IPAQ) was used in three activities of walking, moderate and vigorous physical activity, and sitting [22].  The questionnaires were completed by them at home or in the center. The weight of women was measured without shoes and extra clothes such as coat and veil using the Seca scale with an accuracy of 100 g. The height of women was measured with an accuracy of 0.1 cm without shoes while their back, shoulders, buttocks and heels were in contact with the bar. The BMI was calculated by dividing weight (in kg) by height (in m2). Multiple logistic regression analysis was used to analyze the association of fertility with physical activity, sedentary behavior, and body composition.
3. Results
Infertile women were younger than fertile women (32.44±5.41 vs. 35.10±4.19 years, P=0.001). They also had a lower level of education than fertile women (P=0.001). The level of physical activity (P=0.001) and BMI (P=0.03) in infertile women were lower and higher than in fertile women, respectively. In women with moderate level of physical activity (OR=4.42, 95% CI: 1.60-12.99, P=0.004) the risk of infertility was lower. Women who spend the time sitting for more than 300 minutes a day were 2.07 times more likely to have fertility than women who were physically active (OR=2.07, 95% CI: 1.36-3.14, P=0.001) (Table 1).


4. Discussion
Sedentary behavior is positively associated with leptin secretion, which can reduce fertility by reducing the hypothalamic-pituitary-ovarian (HPO) axis [25]. This down-regulation of HPO affects gonadotropin production, which may lead to menstrual irregularities and impaired ovulation function [26]. In our study, it was found that BMI in infertile women was significantly higher than in fertile women and was independently associated with fertility (OR=1.07). This seems to be a factor confounding the effects of inactivity on regulation of proinflammatory cytokines [27]. In other study, a significant association was also found between sedentary lifestyle and infertility in women [24]. However, it seems that the relationship between physical activity and fertility may vary based on BMI. Wise et al. showed that in women, moderate physical activity increases fertility parameters regardless of BMI [29]. The total level of physical activity (minutes/week) seems to be related to fertility status, although other parameters of physical activity such as duration, intensity, frequency and type can also be considered.  The present study showed that physical inactivity, sedentary behaviors, and BMI in women were associated with infertility, and were its risk factors. These findings emphasize the need to promote active lifestyle for fertility treatment and improving pregnancy and birth rates.

Ethical Considerations
Compliance with ethical guidelines
Ethical approval was obtained from Arak University of Medical Sciences (Code: IR.ARAKMU.REC.1400.050). Informed consent was obtained from all participants and they were free to leave the study at any time.

Funding
This research was supported by the research project (No. 1400.14875), Funded by the University of Arak and Sport Sciences Research Institute. 

Authors' contributions
The authors had equal contribution to the preparation of this article and complied with the standard writing standards based on the ICMJE recommendations.

Conflicts of interest
The authors declared no conflict of interest.

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