MODEL RELEASED. Pregnant woman sitting in a yoga posture. Yoga is a form of exercise that stresses flexibility and relaxation. It also incorporates breathing exercises and meditation. Many women who opt for natural childbirth, giving birth without the use of drugs or surgery, find that yoga aids relaxation and pain relief during the delivery of the baby. This woman is 30 weeks pregnant. A full- term pregnancy lasts between 37 and 42 weeks.