Quoted from ivillage:
In recent years there has been a lot of buzz, both positive and negative, about soy and it's relation to fertility. Tofu and soy are excellent sources of protein during pregnancy. Soy foods contain plant-derived estrogen, known as phytoestrogens. These come in different forms and have different effects. Some may function similarly to estrogens in the body, producing a very weak effect compared to the real thing. And others act as antiestrogens, to reduce the activity of estrogen. Evidence is growing that these phytoestrogens may help with menopausal symptoms, as well as inhibit cancer cell growth. But, a few studies suggest that high levels of soy protein may decrease fertility. These studies tended to look at soy consumption levels that are much higher than most people normally consume. From the reports available, it seems logical to conclude that normal intake of soy proteins will not adversely affect your chances of becoming pregnant or maintaining a pregnancy. But, consuming large quantities of soy products is not recommended.