Pregnancy carries with it a host of symptoms---some interesting, some merely irritating and some desperately uncomfortable. Pain under the navel can be one of the more uncomfortable of these, particularly because it tends to strike with sudden, uncontrollable movements such as coughing or sneezing. There are a variety of causes for this sensation, and as disconcerting as it can be, in most women, it's completely normal.
In their book "What to Expect When You're Expecting," Heidi Murkoff and Sharon Mazel note that the hormones of early pregnancy bring on a variety of changes long before the baby is big enough to physically affect its mother's body much. Early pregnancy hormones, for instance, slow down the digestive tract. This will become very important to the developing fetus---once the placenta is in place, the baby will depend on its mother for all its nutrition, and a slower digestive tract is more efficient at extracting every single calorie from the meals the mother consumes. Unfortunately, a slower digestive tract also extracts more water from food, meaning stools are less frequent and harder in consistency. This constipation can lead to a feeling of bloating, increased gas and generalized abdominal pain.
Dr. Miriam Stoppard discusses another common cause of abdominal pain in her book, "Conception, Pregnancy and Birth." The uterus begins to prepare for the impending growth well before the baby is big enough to begin stretching the boundaries of its home. This involves proliferation of the uterine lining well in excess of what takes place each month during a normal menstrual cycle, as well as some growth of the organ itself. The increased blood flow to the pelvis that assists in both these processes is irritating to the pelvic organs, and can lead to bladder and uterine cramping, both of which can feel like pain behind the belly button. Symptoms due to pelvic congestion typically disappear late in the first trimester.
Round Ligament Pain
The uterus is suspended by the round ligament, which connects the uterus to the abdominal wall. As the organ stretches and cramps, it pulls on and stretches this ligament, resulting in sharp or stabbing pains behind the belly button. Round ligament pain is common even in very early pregnancy, and becomes exacerbated by sudden movements, deep abdominal stretches and occasionally even by pressure. Murkoff and Mazel recommend resting with elevated feet to relieve symptoms.
Starting around the 22nd week, or earlier for experienced moms, many women feel the movements of the fetus through the abdominal wall. Some of the motions are quick and fluttery, while others can be quite sharp, depending upon how hard the baby kicks and where the kick is directed. A well-placed kick toward the inside of the belly button may be uncomfortable, but many women also appreciate this palpable assurance that their baby is, literally, alive and kicking.