The enlarging uterus not only pushes forward on the abdominal wall and down on the pelvic veins, but it also pushes up on the bottom of the rib cage and on the diaphragm (the muscle that stretches across the bottom of the chest cavity and assists in breathing). The rib cage widens, and you will likely breathe slightly faster or you may even feel short of breath.
Urination and digestion are also affected during pregnancy. Pressure from the uterus and hormonal changes affect the urinary tract. The uterus presses against the bladder, which may cause you to urinate more frequently. Hormones cause the ureters (the tubes conducting urine from the kidneys to the bladder) to distend (widen) and the flow of the urine in them to slow. The sluggish urine flow predisposes pregnant women to infection. Hormones, along with the increased blood volume, also cause the kidneys to filter more blood.
However, the kidneys may not reabsorb sugar and protein efficiently because of this increased work load, and these substances may spill into the urine. Since the presence of sugar in the urine can also be caused by diabetes and since the presence of protein can be caused by infection, most doctors screen the urine frequently during pregnancy and may do other tests if any abnormality is found.
The changes in digestion associated with pregnancy are well-known. A pregnant woman's cravings for pickles and ice cream have been the premise of many a joke. You may have unusual cravings and also notice changes in your senses of smell and taste, which may cause you to alter your eating habits. During pregnancy, you may produce more saliva, and the saliva is more acidic, which promotes tooth decay. Your gums are more sensitive and may swell and bleed easily.
In the first trimester, you may have morning sickness, characterized by vomiting and a poor appetite. You may also be constipated. One of the pregnancy hormones causes the muscles of the digestive tract to relax; therefore, they pass the food more slowly through the intestines. In addition, the uterus can press on the colon, inhibiting passage of feces.
Similar mechanisms produce heartburn. The muscles at the junction of the esophagus and the stomach relax, and the uterus presses on the stomach from below, causing the stomach contents to flow back into the esophagus. In late pregnancy, a portion of the stomach may even be pushed all the way up into the chest, producing a hiatal hernia.
A number of changes are necessary in the structures supporting the uterus to stabilize it as it grows. The ligaments in the pelvis and abdomen stretch to accommodate the uterus. In late pregnancy, the upper part of the spine bends backward to compensate for the enlarging abdomen. Hormones loosen the joints of the pelvis in preparation for childbirth.
Your metabolism has also increased during pregnancy, urging you to eat more vitamins and minerals for the growing fetus. Amazingly, your physical changes will all return to normal after you give birth. Read about changes in the metabolism during pregnancy in the next section.