One of my sisters switched from Zoloft to cannabis while trying to conceive. Zoloft is a non-starter if you're planning on conception, and she already had one underweight, failure-to-thrive child (who is robust and healthy now). She is insane when she's off the Zoloft, so smoking instead of drinking to handle her mood swings and mania is, again, a non-starter. Given her propensity to lose appetite, again, cannabis is better for a mother, IMO, than other pharmaceuticals. You have to eat to grow a baby and if you plan on lactating, again, you MUST eat.
Also, if given to sickness during pregnancy, cannabis may be better than the other options. I was very sick during both my pregnancies, spent all day puking up until the third trimester. I wish I had known cannabis might have been an option for me, because the anti-nausea drugs I was given, while strong and got rid of it, also put me to sleep for a good, long time.