What about intercourse?

I’m sure it is hardly necessary to point out that intercourse is inadvisable in early pregnancy if you are experiencing cramping or bleeding or have a history of recurrent miscarriage. As I mentioned before, having had intercourse the night before spotting began is not likely to be the cause of the threatened miscarriage. But, it is known that prostaglanins in semen can stimulate uterine muscle activity and therefore increase contractions. If you have noticed and danger signals, you’d better off abstaining until your doctor feels the pregnancy is secure. Do discuss it with him, however, if you and your husband desire intercourse, as this may still be the best way to alleviate your anxieties and feel you are communicating well as a couple. My advice would then be to avoid deep penetration and to use condoms so the semen does not enter the vagina, thus avoiding the possible effects of prostaglandins mentioned earlier.

One other reason for abstaining is that bacteria can be carried on the sperm. If your cervix is short, or open (that is, if you have a weak, or incompetent cervix), the sperm may enter into the uterus through the cervix, possibly infecting the membranes and then the fetus.