"Pregnancy has a profound effect on the human body, particularly the musculoskeletal system. Hormonal changes cause ligamentous joint laxity, weight gain, and a shift in the center of gravity that leads to lumbar spine hyperlordosis and anterior tilting of the pelvis. In addition, vascular changes may lead to compromised metabolic supply in the low back. The most common musculoskeletal complaints in pregnancy are low back pain and/or pelvic girdle pain."
https://www.ncbi.nlm.nih.gov/pubmed/26271756
"Yoga is a mind-body practice that encompasses a system of postures (asana), deep
breathing (pranayama), and meditation. Over 36 million Americans practice yoga of which the majority are reproductive-aged women. Literature to support this practice is limited, albeit on the rise. A prenatal yoga practice has been shown to benefit women who suffer from anxiety, depression, stress, low back pain, and sleep disturbances. A small number of studies have been performed in high-risk pregnancies that also demonstrate an improvement in outcomes. The safety of performing yoga for the first time in pregnancy and fetal tolerance has been demonstrated." (Journal of Clincial Obstetrics & Gynaecology)