These findings support the previous findings in the literature that the prevalence of amenorrhea and oligomenorrhea is high in athletes. Females practicing endurance and weight-class sports had a significantly higher risk of these disorders. There was also a positive association between the disorders and the following: age under 20 years old, late onset of menarche, and use of OCPs. Intensity of training sport or BMI were not risk factors. About one sixth of the athletes with amenorrhea/oligomenorrhea were diagnosed as PCOS.
To our knowledge, this is the first study in Iran to evaluate risk factors of amenorrhea and oligomenorrhea in athletes. A particular strength is its high response rate, which led to a large sample size. We invited all possible top female Iranian athletes from 34 sports federations, including female medalists in Tehran and female members of national teams. Very high percentages (95%) were included in this study. Another strength of this study is that it presents the prevalence of PCOS in women athletes, which has not been evaluated earlier.
Like earlier studies, we demonstrate that prevalence of amenorrhea/oligomenorrhea in athletes is high. Having compared the prevalence of amenorrhea/oligomenorrhea in our study with the prevalence in the general population reported in a review by Pfeifer and Patrizio , we conclude that these disorders are more frequent in athletes. However, as there are no reliable data on prevalence of amenorrhea/oligomenorrhea in the Iranian general population, we have not been able to compare our data with those of our population.
Like other studies [1, 9, 10], we show that amenorrhea/oligomenorrhea occurred significantly more in weight-class and endurance sports. The probable reason lies in weight-class athletes' focus on leanness and low body weight. They believe that the chance of success is higher if they can participate in the lowest possible weight category. This very belief leads to increased efforts to losing weight. To increase their performance, athletes in endurance sports tend to lose weight.
Unlike other study  and a report by the IOC , we detected no association between aesthetic sports and amenorrhea/oligomenorrhea. The disparity is probably explained by the fact that only two aesthetic sports were represented in our study: aerobic sport and vosho. None of the participants in this group reported any amenorrhea or oligomenorrhea. No participants did ballet, figure skating, or synchronized swimming. Menarche had not started in any of the gymnasts who responded, who were therefore not included in this study.
In recent years, some studies have reported significant relationships between menstrual disorders and late-onset menarche in athletes. In 2007, Micklesfield et al. studied menstrual disorders in 613 marathon and half-marathon runners in South Africa . As in our study, they showed that onset of menarche was later in the group with amenorrhea/oligomenorrhea than in the group with regular menstruation. Menstrual disorders and late onset menarche both seem to have caused by intensive training and inadequate energy intake 
Our study also shows that participants aged under 20 reported more amenorrhea/oligomenorrhea than older participants. Readers are reminded that we excluded all participants who were in their first year of menarche and who had reported amenorrhea/oligomenorrhea, which we considered to be a physiological event. The experience of Iranian obstetricians is that these disorders are more likely to occur before the age of 20, even in girls who practice no sport. Their higher prevalence in athletes younger than 20 years seems to be due not to sporting activities, but to the immaturity of the girls' reproductive systems.
Although it has been shown that a certain percentage of fat mass is required for menstruation to begin and to continue regularly, no specific percentages have been reported [13, 14]. This number seems to vary from person to person. Unlike other studies, we found no significant relationship between amenorrhea/oligomenorrhea and BMI (BMI < 20 and BMI > 25) . The explanation may lie in the fact that many aesthetic sports which require extreme leanness (such as ballet, dance, figure-skating, and synchronized swimming) are not practiced in Iran. Moreover, the criticism of the use of BMI for body composition on assessment are that it is a relatively poor predictor of body fat percentage and it results in inaccurate classifications (normal overweight, obese) for some individuals . Unfortunately, due to feasibility reason, we were unable to use more advanced methods such as measurement of skin fold, or bioelectrical impedance analysis to estimate body fat percentage.
Studies by the International Olympic Committee have reported a higher prevalence of amenorrhea/oligomenorrhea in athletes who seek to improve their physical performance through strict dietary restrictions or through strenuous exercises intended to induce weight loss . The study by Torstveit et al. also showed that weight-class athletes use pathologic methods of weight reduction more than other athletes . Another studies also confirm that menstrual dysfunction is more prevalent among athletes who focus on losing weight and becoming thinner . Although Torstveit et al. reported a relationship between weight-reducing drugs and amenorrhea/oligomenorrhea , we observed no such relationship in our study. This may have been due to small number of participants who reported using such drugs. It appears that some participants may have denied using weight-reducing drugs out of fear of expulsion from the team, and out of fear of their parents' and coach's objections, etc.
Although, unlike Drinkwater et al. , we found no association between amenorrhea/oligomenorrhea and the intensity with which sports were practised, our results agreed with those of two other studies [18, 19], which reported no difference between training intensity among amenorrhea and eumenorrhea athletes. Because we had no clear or reliable reports of abrupt onset of intense training, we could not evaluate whether there was any association between the onset of amenorrhea/oligomenorrhea and a sharp increase in sport intensity.
A review by Loucks et al. in 2006 stated that the prevalence of PCOS in women athletes has never been assessed or reported. To our knowledge, our study is therefore the first on the prevalence of PCOS in women athletes. However, we should remind readers that we assessed PCOS in any participants with clinical symptoms of amenorrhea/oligomenorrhea, but not in those who had no mentioned of these disorders. Because some PCOS cases might show any clinical manifestation, we may have underestimated the prevalence of PCOS.
Haberland et al. reported in a survey in 1995 that over 90% of sports medicine doctors or family physicians prescribed estrogen replacement to treat athletic amenorrhea  The positive association we found between amenorrhea/oligomenorrhea and the use of OCPs might therefore be due to the prescription of OCPs for treating menstrual irregularities.
It should be pointed out that this study evaluated Iranian female athletes in organized sport federations. As stated above, the variety and frequency of these sports was not necessarily the same as those of leading women's sports in other countries: for example, ballet, figure skating, and synchronized swimming are not represented in any sport club in Iran. Although women's sports have been brought some difficulties by Islamic dress codes, they are nonetheless progressing slowly and steadily. As the number of professional women's clubs is very low, there are not many high-level competitions; similarly, international competition is subject to considerable limitation. We believe that the difference between our results and those of studies in non-Islamic countries are partly a consequence of these differences.
Future studies among Iranian female athletes should examine preventable risks, such as inappropriate dietary restrictions, pathologic methods of weight loss, psychological and physical stress, and athlete's personality types.