Is it safe to drink soy milk while pregnant?

Very likely, yes. The only theoretical concerns with soymilk lie in the fact that soy is high in isoflavones and phyto-estrogens, plant hormones which act as weak estrogens in the body. Trying to determine their exact effect has been difficult. One study linked levels of soy consumption of the pregnant mother inversely to the male child's penis size- the more soy consumed during pregnancy, the smaller the penis, but this was only an observational study, not an experimental one, so it's not known if the soy actually caused a reduction in penis size, or if other factors were at play. Again, it's not as though the study could pinpoint soy as the cause for these findings. A moderate soy intake will probably not cause any trouble. Consult your OBGYN if you have any other questions.