Is it appropriate to receive Communion if you have nausea from morning sickness and there is a potential that you may vomit shortly after Mass?
At Communion time, if you know you are in danger of vomiting, then it is appropriate to refrain from receiving Communion. If you do not know, or believe that everything will stay settled for at least fifteen minutes (which is considered to be the amount of time the Real Presence remains after ingestion), then you may receive Communion. If you miscalculate, don’t worry about it; you are not at fault for anything you do not will. This would hold true for anyone who believes themselves in danger of vomiting, whether or not it is caused by morning sickness.
By the way, those who are seriously ill should consider staying home from Mass. If this is a Sunday or holy day of obligation on which one is nauseous, such illness would dispense one from the obligation to attend Mass.
Attention, Cold & Flu People at Mass! by Jimmy Akin