At 31 weeks pregnant, you're in the golden period of pregnancy. You're over the early pregnancy symptoms of nausea and fatigue. The later symptoms of joint pain, heartburn and swollen feet probably haven't made their appearance yet. Beyond experiencing an ever-expanding waistline, you can expect a number of symptoms and physical changes to develop as pregnancy progresses and labor approaches.
As pregnancy progresses, the joints in the pelvis loosen to allow the pelvis to expand slightly and make delivery easier. While beneficial in the long run, this change can make it uncomfortable and difficult to walk as the baby's weight increases. Your posture may change as the normal curve of the lower spine becomes more exaggerated under the relaxing influence of progesterone. This change also puts additional pressure on the muscles and ligaments in the back, often causing back pain. Around 12 percent of pregnant women experience restless leg syndrome, report the authors of a study published in February 2013 in the journal "Neurology."
The third trimester of pregnancy brings a number of skin changes. Pruritis -- the medical term for itchiness -- can drive some pregnant women crazy. There are many possible reasons for itchiness during pregnancy. For example, a rash called pruritic urticarial papules and plaques of pregnancy, or PUPPP, can cause intense itching of the skin on the abdomen, often around stretch marks. Some women with preexisting dermatitis experience worsening of their symptoms during pregnancy. Other women develop itchiness related to sluggish gallbladder function during, which causes deposition of irritating bile salts in the skin. Many women experience darkening of the skin on the cheeks and around the eyes known as chloasma or the "mask of pregnancy." A line between the navel and pubis, called the linea nigra, often darkens as pregnancy progresses.
As pregnancy progresses and your uterus grows, you might become more aware of your abdomen tightening and relaxing at times. Called Braxton-Hicks contractions, these early "practice" contractions tone the uterus and often start thinning and dilating the cervix in preparation for labor and delivery. Unlike labor contractions, Braxton-Hicks contractions are most often felt in the front of the abdomen and spread downward. Labor contractions often start in the back and circle around to the front. Braxton-Hicks contractions may disappear if you change position or move around. True labor isn't affected by position or activity changes. Braxton-Hicks contractions usually do not cause pain.
As pregnancy progresses in the last trimester, constipation and heartburn can cause discomfort from one end of the gastrointestinal tract to the other. High levels of progesterone -- a hormone produced by the placenta -- can also cause the muscular contractions in the GI tract to slow down. This allows food to sit longer in your GI tract, increasing both heartburn and constipation. Your growing baby also puts pressure on the stomach, increasing acid reflux and heartburn. Iron supplements to treat pregnancy-related anemia can exacerbate constipation.
As many as 70 percent of women experience swollen feet and legs in the latter part of pregnancy, according to the medical text "Obstetrical Dermatology: A Practical Guide." The enlarging uterus impairs blood flow from the lower extremities back to the heart, causing edema, or swelling. Water and sodium retention also contribute to edema, which occurs around the eyelids in 50 percent of pregnancies.