Sex is normally safe. If you have any complications during your pregnancy, either you or your partner may be scared to have sex without really saying anything. There are some pregnancy problems that make it unsafe to have sex but normally it is fine. Some couples have heard from other people that they shouldn't have sex while pregnant or that there are restrictions. If you're not sure, ask your doctor.
Not predictable. Sex life varies so much from one person to the next that it's hard to say how you will feel. In the first trimester, most women don't feel that well physically and may not feel like having sex at all. Many will have an increase in sex drive over their normal in the 2nd trimester. They may also having chafing after sex, that can be relieved by using a lubricant, and cramps related to orgasm.
In different ways. Orgasms may be more intense, with more cramping. Rarely, you may have bleeding after intercourse, from the cervix. As the uterus grows, intercourse may become uncomfortable.