Although some couples abstain throughout pregnancy, most have sex at some time, and many couples go on through pregnancy with wild abandon. This is only between the two of youwhat is right is what works for you as a couple. The only guidelines have to do with safety and comfort.
The guidelines:
All sexual activities that dont hurt you are considered safe, with the exception of blowing air into the vagina, which can allow the air to get into your bloodstreama potentially fatal situation.
Beyond about 18 weeks, the woman shouldnt lie flat on her back for long periods of time, as the weight of the uterus can interfere with circulation and the flow of blood to the baby. However, if you just put a pillow under your right hip and tip yourself to the left, your circulation should be fine.
Late in pregnancy your tummy may get in the way, and you will need to choose positions that feel comfortable. Try side-lying or doggy style with the man behind, or any position in which the woman is on top.
Generally if you are having any bleeding or are at risk for delivering prematurely, you may be advised to abstain from intercourse and/or from orgasm. If you are having any complications of pregnancy, be sure to check with your doctor or midwife to see which aspects of sex are OK.