Alternatives: As the old saying goes...there is more than one way to skin a cat. If for any reason intercourse is not enjoyable or advisable, then showing affection through oral stimulation can offer an alternative. While there is an extremely rare but serious condition called air embolism that can occur in pregnancy as the result of cunnilingus, it is not a significant worry as long as air is not blown directly into the vagina. But if your partner has had a cold or sore throat it may be advisable to abstain as Beta Strep (Strep B), a growing cause of concern in medical circles because it can result in life-threatening infections in the newborn, can be passed in this way. And there is absolutely no risk to either mother or baby from performing fellatio, even if she chooses to swallow the ejaculate.
Orgasms: The female orgasm may result in a significant tightening of the uterine muscle, but this should not be a concern. This contraction is very similar to Braxton Hicks contractions. The tightness should disperse within about five to ten minutes. There is no need to worry that you are starving the baby of oxygen during this time. Just the opposite in fact, the female orgasm results in a significant increase in blood supply to the uterus. As a result you may notice that the baby is slightly more active afterwards, but this is fine. As for the male orgasm, there are actually chemicals in the male ejaculate which can aid the cervix in softening and ripening (natural version of the ones they use to induce labour in smaller quantities). So it is NOT a myth that sexual intercourse close to term can help kick start labour.
Baby: There is absolutely no scientific or even valid anecdotal evidence of causing either physical or psychological harm to the unborn baby by engaging in sexual relations. All of the jokes and funny stories aside, your child is safely ensconced in your womb. Your cervix prevents any penetration from hurting the foetus throughout the complete term of a normal pregnancy. It may seem odd if junior suddenly starts doing somersaults in there, but this is the result of your increased breathing and heart rate that results in a significantly noticeable proliferation of oxygenated blood to the baby. Just realise that...and have a sense of humour. This is not the last time the baby will interrupt mummy/daddy time.
These nine months are the beginning of your new life-long adventure in parenthood. But they are also probably the last opportunity you have to be 'just' a couple for at least eighteen years...except for occasional dates and trips of course. This new life that the two of you have created together will make you grow and learn in many ways...physical and mental. With good communication and some creativity, they can also be a wonderful time to explore your sexuality or to focus upon other types of intimacy. So explore your options and enjoy these new forms of intimacy.