If you're having a normal pregnancy, sex is considered safe during all stages of the pregnancy.
So what's a "normal pregnancy"? It's one that's considered low-risk for complications such as miscarriage or pre-term labor. Talk to your doctor, nurse-midwife, or other pregnancy health care provider if you're uncertain about whether you fall into this category. (The next section of this article may help, too.)
Of course, just because sex is safe during pregnancy doesn't mean you'll necessarily want to have it! Many expectant mothers find that their desire for sex fluctuates during certain stages in the pregnancy. Also, many women find that sex becomes uncomfortable as their bodies get larger.
You and your partner need to keep the lines of communication open regarding your sexual relationship. Talk about other ways to satisfy your need for intimacy, such as kissing, caressing, and holding each other. You also may need to experiment with other positions for sex to find those that are the most comfortable.
Many women find that they lose their desire and motivation for sex late in the pregnancy - not only because of their size but also because they're preoccupied with the impending delivery and the excitement of becoming a new parent.