With all the changes that take place during pregnancy, it's easy for women to wonder whether what they're feeling is normal or a sign that something is wrong---particularly when what they're feeling is painful. The pelvis and abdomen undergo significant changes during pregnancy, making them the site of many of an expectant mother's aches and pains. Some of the discomfort is normal, and other pains indicate problems. Pain localized to the right side of the abdomen may have several possible causes.
In her book, "Human Physiology," Dr. Lauralee Sherwood explains the role of the ovaries in early pregnancy. While the ovaries produce and ovulate the egg that is fertilized during conception, these organs are also responsible for maintaining the integrity of an early pregnancy, until such time as the placenta has formed. After ovulation, the ovaries secrete high concentrations of estrogen and progesterone, which work together to maintain the lining of the uterus, into which the fertilized egg implants. The ovaries continue secreting these hormones until around the fourth month of pregnancy, at which point the placenta takes over. During this time, it's common for a cyst to form on the ovary that ovulated the egg that was fertilized to produce the pregnancy in question. These cysts, while generally harmless, can be uncomfortable. If the cyst is located on the right side, it's common for women to experience aching or stabbing pain in the right lower abdomen until around the fourth month of pregnancy.
Under normal circumstances, a fertilized egg migrates through the fallopian tube to the uterus, where it implants. Sometimes, however, blocked or damaged fallopian tubes cause eggs to implant in the tube itself. This is called an ectopic pregnancy, explain Heidi Murkoff and Sharon Mazel, in their book "What To Expect When You're Expecting." If the right ovary ovulates, the egg is fertilized in the right fallopian tube, and damage to the tube results in tubal implantation, women will begin their pregnancies with normal symptoms and without pain. Eventually, however---generally starting around six weeks of gestational age---the right lower abdomen will become painful and tender as the fallopian tube becomes irritated and begins to stretch. Pain increases with time, localizing and becoming stabbing in nature. Untreated, ectopic pregnancies can be fatal to the mother, so once diagnosed, they are terminated.
The uterus is suspended by several ligaments, which are tough bands of connective tissue that attach it to the abdominal wall. As a pregnancy develops, the uterus begins to grow and stretch. This causes the ligaments to stretch, notes Dr. Raymond Poliakin in his book, "What You Didn't Think To Ask Your Obstetrician." Pain is commonly localized to one side of the lower abdomen or another---it generally doesn't occur across the entire abdomen at once. If a woman is beyond her fourth month of pregnancy, such that the pain isn't due to ovarian cysts or an ectopic implantation, lower right abdominal pain may often be due to ligament stretching---particularly if the pain comes on suddenly, is in response to standing or sneezing, and disappears quickly.