That happened to me too during my first trimester... although i didn't vomit blood, i was coughing it. She must have an internal injury, a lung perforation or so. When you vomit blood is one of two things: either you have an injury inside of the lung, or you have an injury somewhere else that is bleeding to your stomach and you vomit blood cause of this. The stomach has a thing for not allowing too much blood be ingested, hence why you would puke it out. Regardless, you should go to the ER asap.
i started doing that in my last trimester because my acid reflux was so bad that it was burning my throat and causing it to bleed. zantac was the solution but she should see her OB and talk to them about it.
has your girlfriend being severely sick in the first trimester? sometimes you can have whats call hyperemis gravidarum which basically means excessive sickness in pregnancy. i had this when carrying my first child and worst of it started at 4 weeks pregnant, it peaked at 12-17 weeks pregnant where i was sick 30 -50 times a day, this led to me vomiting some blood in small amounts, due to bursting blood vessels when retching, and the stomach lining being irritated due to volumes and frequency of vomiting, if your girlfriend has similar symptoms it may be worth seeing your gp/ or maternity consultant as this condition can lead to dehydration, if it not these symptoms your GF has then id see your GP anyway to get her checked out.
i now have a healthy happy boy of nearly 2 years, he wasn't affected by vomiting.
hope it improves for you all
xx
If she is vomiting blood, she really needs to go to the ER IMMEDIATELY!!