There has been a lot of evidence that is being ignored by the medical community which shows that cannabis may be healthy for the fetus and the baby. The following link has some good research, however, make sure you understand the laws of your area. I remember reading somewhere that some hospitals that do drug testing will consider it child abuse if they find proof of cannabis use.

Here are the articles:

DREHER'S JAMAICAN PREGNANCY STUDY

Ganja Mother, Ganja Babies