Only after they are born, they may vomit merconium if they aspirate it before being born. They may also vomit poop if they have intestinal blockage
If you are planning on taking Castor Oil to induce labour it's method of working is to upset the mothers stomach causing diarrhea. This in turn stimulates the uterus to contract and begin labour. However, the castor oil absorbed by the mother and be passed on to the baby causing the baby to release its bowls. This can lead to fetal distress during labour and the aspiration of merconium during the birth process (ie. the substance expelled from the baby's bowels) - fetal distress my result in interventions such as a c-section and aspiration of merconium would lead to breathing problems in the newborn.
ok im not exactly sure how long because the placenta is such a hoarder but id wait like a week before that three month drug screen they give because they don"t test baby merconium for benzos