Carbon dioxide. Carbon dioxide (chemical formula CO2) is a colorless gas with a density about 60% higher than that of air (1.225 g/L) that is odorless at normally encountered concentrations. Carbon dioxide consists of a carbon atom covalently double bonded to two oxygen atoms.
You should only do ballet in pregnancy if you are used to it. Ballet stretches can place a lot of pressure on your joints, especially your pelvic joints, and standing on one leg can cause pain in your pelvis.
The safest time to fly during pregnancy is before 37 weeks or, if carrying twins, before 32 weeks, new advice says. The Royal College of Obstetricians and Gynaecologists says flying is not harmful during a low-risk pregnancy, but there may be side-effects.