Many women are surprised to learn that even very early in pregnancy, it's possible to feel -- and look -- several months pregnant. This is due to abdominal bloating, which begins as early as the first few days after conception and can last well into the first trimester. Although weight gain and true maternity clothes are many months away, newly pregnant moms can feel as though their pelvis is quite full. It's not uncommon to see the beginnings of a tiny baby bump, although the bump isn't actually because of the baby just yet.
During the fourth week of pregnancy, a fertilized egg is implanting in the uterine wall. Until the placenta develops, the blood vessels of the endometrium -- the spongy lining of the uterus -- provides nourishment for the developing embryo. The endometrium proliferates and thickens in the early weeks of pregnancy to support the developing embryo. Increased amounts of blood also flow to the womb, enhancing uterine swelling. The rapidly thickening lining of the womb and associated swelling cause the uterus to take up more room in the pelvic cavity, often leading to a bloated, congested feeling in the lower abdomen.
Hormone levels in early pregnancy dictate changes in a woman's body that prepare it to support the developing fetus throughout the pregnancy. The hormones progesterone and relaxin -- which allows the pelvis to stretch so that a baby can pass through during delivery -- surge beginning very early in the pregnancy. These hormones cause relaxation of the digestive tract muscles, which slows the rate of food passage through the small and large intestines. Naturally-occurring bacteria in the gut are, therefore, given more time than usual to digest food matter. This often leads to increased intestinal gas production. For this reason, pregnant women have more gas than those who are not pregnant, and this can contribute to bloating.
As the gut slows down, food reaches the end of the intestine -- the rectum -- more slowly than it normally would, leading to less regular bowel movements. As food sits in the intestines for a prolonged period, the extraction of nutrients and water from the food you eat becomes more efficient. This will eventually be of great benefit to the fetus. A slow intestine is better at extracting all the nutritional content from each of mom's meals -- but may cause uncomfortable side effects. Less water content leaves stools drier than usual. These dry stools are particularly slow at completing their journey to the rectum, and built-up fecal matter in the lower gastrointestinal tract is yet another cause of maternal bloating early in pregnancy.