Research has shown that regular practice of yoga in pregnancy provides specific benefits to mum and baby during pregnancy and beyond: 

• Lower stress levels during pregnancy
• Less pregnancy complications. Back pain related to pregnancy responds well to regular yoga practice and many other aches, pains and common ailments of pregnancy may be relieved
• Increased suppleness, strength, and flexibility in the joints and important muscle groups that are used in labour and birth. The pelvic floor muscles are strengthened and toned
• Regular yoga improves breathing and circulation, thus increasing the oxygen supply to your baby. Breathing awareness also encourages relaxation and the release of tension. Regular practice of relaxation during pregnancy enables you to tap into these sensations during your labour, helping you cope 
• Encourages your baby to adopt a favourable position for birth
• Shorter duration of labour
• Helps to open the pelvic outlet by simulating squatting and other upright postures (squatting can open the pelvic outlet by up to 30%!)
• Less pain during labour
• Improved quality of sleep and the pregnancy feels less tiring
• Increased confidence, sense of empowerment and optimism
• Creates a more sensitive and receptive relationship with your baby, enhancing your nurturing and mothering instincts in readiness for motherhood
• Enables you to get in touch with your inner feelings and intuition

The Effects of Prenatal Yoga on Birth Outcomes: A Systematic Review of the Literature. Riley K, Drake E (2013)

Oxford Handbook of Midwifery. Medfort et al. (2006)