The pregnant uterus is not anywhere near the vagina, and your baby is kept safe and snug in there with the help of the amniotic sac and the uterine muscle. The so-called mucus plug prevents anything that could cause an infection from entering the uterus. A female orgasm might result in Braxton Hicks contractions, but these are harmless. In general, pregnant women can continue to enjoy great sex, though the positions that are comfortable for them are likely to change as their pregnancy progresses. Don't expect that the missionary position will be something to even consider in your third trimester, for instance! There are some exceptions to the rule of pregnancy and sex being a perfectly fine combination.
When do you need to abstain from intercourse or at least seek advice from your healthcare provider? Let's take a look.If you notice spotting after intercourse. If you experience abdominal cramping during or following sex. If you have an incompetent cervix. If you have placenta previa. Once your water has broken. If you have been put on bedrest.
Some of these, like a broken water and placenta previa, definitely exclude the possibility of sex. Other situations need to be discussed. If you feel uncomfortable in any way, don't be embarrassed to call your doctor to ask about it that is what they are there for!