A lot of pregnancy symptoms can be blamed on hormonal changes, but a good number of them are also the direct result of having a baby take up all that room inside your body – room that used to belong to your lungs and stomach and digestive system.
If you could look into your body before you are pregnant, you would see that most of the space in the abdomen is taken up by the large and small intestine. There is no real separation between the pelvic and abdominal cavities. The chest cavity, containing the heart and lungs, is separated from the abdominal cavity by a large muscle, the diaphragm.The left-hand image shows a woman’s body before she gets pregnant, and the right-hand image shows her body carrying a full-term fetus. See how squashed your bladder is? Look at the way your stomach pushes up against your lungs. Check out what’s happening to your intestines! No wonder everything feels so crowded in there.
Below the diaphragm is the left side of the liver, above and in front of the stomach. In this cross-section, the descending colon, small intestine, transverse colon, and
stomach hide the gall bladder, ascending colon, and portions of the liver and small intestine in the right side. The ribs are visible beneath the right breast. The symphysis, coccyx, sacrum, some vertebrae, and the spinal canal are also shown.
Behind the symphsis are the bladder and the urethra, which extends from the neck of the bladder to the urinary opening in the vestibule of the vulva. In front of this opening is the clitoris. Behind the bladder and urethra is the vagina. The uterus, in its normal position, is above and behind the bladder, with its cervix protruding into the vagina. The pelvic colon, rectum and anal canal are behind the vagina and uterus.
The individual organs accommodate themselves to the changing conditions of those that surround them and to the size and shape of the body cavity. The configuration of the bony framework and the tone of the muscle walls – determined by heredity, age, nutrition, disease, injury, and habitual posture – control the size and shape of the body cavity.
This picture shows the usual position of the baby at term, which is 40 weeks of pregnancy, with the head occupying much of the pelvic cavity. The canal of the broad, enlarged cervix is still filled with the plug of mucous. If this is your first pregnancy, the external os, the small opening at the bottom of the cervix, is usually not dilated, whereas if you have given birth before, it will often admit two fingers some time before labor begins. The vagina, which gradually becomes softer, more expandable, and elongated when the uterus rises, seems to shorten when the head enters the pelvis and pushes the cervix into the vagina.
The bladder is compressed between the baby’s head and the pubic bones, with no room for expansion except up into the abdominal cavity. The pelvic colon is pushed up out of the pelvis and compressed against the sacrum. Pressure on the blood vessels at the brim of the pelvis interferes with the return circulation from the swollen veins in the vulva, anal region, and lower extremities.
Common discomforts you may experience during the last weeks of pregnancy are frequent urination, increased constipation, edema (water retention), and aching of the legs and vulva, as well as varicose veins in the vulva, rectum, and legs. These can be explained by several factors, including the position of the uterus, the pressure of the baby’s head, the loss of muscle tone, the increased muscularity of the tissues, and the added volume of blood distending the vessels in the pelvic cavity, perinea region, and lower extremities.