OCD-associated stress and anxiety (either chronic or acute) can really throw off fertility, as in any stress and anxiety disorder. Although the psychological consequences of infertility are evident, it is not so clear how psychological disorders can affect fertility.
In women, unhealthy stress reaction of the body may break gonadotropin-releasing hormone pulsation (GnRH; utmost importance in controlling the menstruation cycle) and lead to anovulation when the ovaries do not release the egg during a menstrual cycle. The egg cannot meet the sperm, and hence not fertilized.
The mood disorders in man may also lead to decreased fertility through the induction of some sexual disorders (e.g. erectile dysfunction or ejaculatory disorders) and through the negative impact on semen quality caused by hormonal imbalance. Sexual dysfunction may cause difficulty conceiving. And vice-versa, attempts to conceive may cause sexual dysfunctions.