In general, it’s safe to crack or pop your back during pregnancy as long as you exercise some caution.
Joint cracking or popping, called cavitation, is caused from a pressure change within your joint and is often the result of spinal manipulation therapy. This change in pressure allows dissolved gas to escape from the joint, which results in the audible pop. Spinal manipulations influence the surrounding tissues and nervous system to decrease restriction and pain levels. You may notice that your back pops on its own with certain movements or stretches; this may happen more during pregnancy due to the hormonal influence on joints contributing to hypermobility.
If you feel like you have to constantly pop your back to feel relief, it may be beneficial to work with a physical therapist or chiropractor skilled in working with pregnant people. There have been few adverse events reported after spinal manipulation during pregnancy, but it’s always best to discuss risks and benefits with your provider to decide what treatment is best for you.