Important to seek professional help in this sort of matter. However, I bled in the first trimester with my first pregnancy, and my doctor's opinion (and, even though they are doctors, you should still take their advice with a grain of salt) was that sex, in most cases, is perfectly fine, and that if one is going to miscarry it's regardless of whether they have sex or not. As well as seeking a medical opinion, you should go with instinct. Sometimes sex is slightly dangerous. MOst of the time, bleeding is just a normal part of pregnancy (many pregnant women bleed - some women don't find out they're pregnant for many months because they still experience a "period" and go on to have healthy babies. It really depends on the cause of the bleeding.