A pregnant woman (as well as not pregnant) must pray until she's conscious. However, Shariah is soft in relation to patients, such as pregnant women, how to pray.
If it is hard to stand, she can pray sitting and can do half-length bow and prostration while sitting, touching the ground. If she can not sit, she can pray in bed / reclining / lying on the right or left side, as it is convenient. In this position, she can do half-length bow and prostration, as we mentioned above. If she can not, she can pray lying on her back, facing the Kaaba and expanding feet to the Kaaba and commit half-length bow and prostration, as we mentioned above.
If it is difficult to perform half-length bow and prostration, she can do it by moving with head, and that will be enough. If she can not move, she can imitate prayer movements with her eyes. If she can not do it, she can imagine the movement of prayer in her heart, and Allah, with His infinite mercy will accept such a prayer from this woman, as He, the Most High, said: "Allah does not intend to make difficulty for you, but He intends to purify you and complete His favor upon you that you may be grateful".