During pregnancy, the amount of air moved in and out of the lungs increases by nearly 50% because:
Each breath contains a larger volume of air
The rate of breathing (breaths per minute) increases slightly
As the growing baby crowds the mother's lungs, many mothers have less room to breathe and will get short of breath.
The muscles in the walls of the gastrointestinal system relax slightly, and the rate at which food is squeezed out of the stomach and along the intestines is slowed down.
The growing baby crowds the mother's stomach - pushes it higher than usual - and can cause indigestion and heartburn. The acids in the mother's stomach that help digest food are pushed up into her chest, where they cause a burning feeling.
As the growing uterus presses against the bladder, the need to urinate becomes more frequent.
There is an increase in the amount of urine produced as the mothers' kidneys must work extra hard to filter her own waste products from her blood plus those of the fetus, and get rid of them in her urine.