Sex can be a difficult and sensitive subject during pregnancy, no question!
It's best to clear up some common misconceptions to maintain a healthy sex life:
1. The baby simply will not be able to see your penis (yes some men actually say this!)
2. You will not hurt the baby (however it might be painful or uncomfortable for your partner - try different positions)
3. Women are not less attractive during pregnancy, in many cases her more curvy features will be a turn on for you and her!
4. You will not induce lactating by gentility stimulating her breastal region (just make sure to not overstimulate and be gentile, they may be sensitive.
5. Her belly will not get in the way, you just have to be more creative with positions.
6. There are times where she will not want you near her, however, be patient, there are also times (more in the 2nd and 3rd trimesters) when she may want you more!
Overall, it's best to maintain open communication with your sex life and make sure to talk about it. If you don't talk about it you may be neglecting each other which will possibly make her feel unattractive and cause you to feel unsatisfied.
Compromise, figure out the time and positions that feel best for both of you and work with each other to enjoy sex.
For more information visit: http://www.babycenter.com/sex-during-pregnancy-overview