Someone asked how they could use yoga to help with some sciatica that they started experiencing during their pregnancy.
Having never met them, this is what I felt like i could safely offer.

most generally, sciatica is caused by the irritation, compression, and/or inflammation of the sciatic nerve.

see, the sciatic nerve comes down the vertebrae and weaves through the pelvis, it passes under a part of the pelvis called the sciatic notch (bone). then it travels down through the glut and the hamstring.

often, what can happen, is through alignment, tension, injury, etc, is that the notch rubs against, or crushes the nerve. this is irritating. also, if there is a possibility that the nerve can get squeezed by the glute and the hamstring pushing, or being stuck together.

the best thing to do it to create space in the jammed areas, and be really mindful of your not making it worse by doing poses that jam up the area.

some poses that might be useful:
*pigeon pose while lying on the back, you can do it the normal way, if your hips are really open
*pascimottanasana with the knees deeply bent and the spine straight, to peel open the tissues in the back of the legs and butt. deeply bent knees, really really
*try putting two straps around your hips, pull one to the left, and pull one to the right. this can help open the pelvis nicely. you can keep them on while you do your practice, and it might support you nicely
*twisting triangle
*easy locust pose that will strengthen the low back muscles

avoid
*deep forward folding with legs straight
*deep backbends that jam the sacrum

hope it helps.