If your partner is pregnant, then it can be wonderful and terrible news at the same time. If you have been planning it for a while, then it is a miracle, but when you are horny, it is not always so, depending on which month she is in. The first three months can be either a blessing or a curse. The sudden change in her hormone levels give her morning sickness, she gets aversions for certain food, and she might also turn her back at sex. Luckily, it is not always the case, especially if you support her when she feels bad. In that case, at least mutual masturbation is possible, but she is likely into something else, as well, especially as the second three months are coming.
Then you can do anything. She will be so horny that she would be willing to have sex all day, and even if she would say no to something under different circumstances, she will say yes to almost anything in this period, so have fun as long as you can!
As her belly is growing, sex will become more and more of a challenge for both of you, but if her belly is not pushed on, then it is safe even if you do it right before her water would break. It includes doggy, her on top, of even spooning. In these last three months, you can only turn her down by letting her think of herself as ugly. Always make sure that she knows how sexy she still is in your eyes!