This is primarily due to excess estrogen interfering with normal ovulation in women[1] and altering spermatogenesis in men.[19] It is believed to cause 6% of primary infertility.[5][20] A review in 2013 came to the result that obesity increases the risk of oligospermia and azoospermia in men, with an of odds ratio 1.3.[21] Being morbidly obese increases the odds ratio to 2.0.[21]