I had gastro at 20+ weeks. It was horrible, i thought i was going to induce labour. And yes it came out both ends. Lasted 24hrs thank goodness but my 2yo had it for a complete 10 days the whole time i was pregnant and passed it on to DH as well. As far as my knowledge, the microbes involved can't be passed onto the foetus. All is well inside the sac that protects them from the nasties we mothers get exposed to. You do need to keep an eye on your fluids and nutrition if you are throwing up heaps.