The second trimester, lasts from the beginning of the 13th week of pregnancy until the end of the 27th week, and is sometimes called the “Golden period” of pregnancy. This is when many of the side effects of early pregnancy have diminished. Also you are likely to find that your nausea is easing off, you are sleeping better and your energy is returning. The risk of miscarriage is lower than that in the first trimester. Your enlarging abdomen will begin to be much more noticeable by four or five months.
Now is the time you’ll also want to think about childbirth classes for you and your partner. During the mid–trimester, more blood is produced to supply the placenta with oxygen and nutrients for your baby’s growth. Your digestive system slows the rate at which food moves through your system. And every organ system in your body continues to adapt to pregnancy under the influence of increasing hormone levels. These and other changes may give rise to some of the signs and symptoms described here.
During pregnancy this period the joints between your pelvic bones begin to soften and loosen in preparation for the baby to pass through your pelvis during birth. In the second trimester, your uterus becomes heavier, changing your center of gravity. Gradually–and perhaps without even noticing it–you begin to adjust your posture and the ways in which you move. Another reason for the back pain may be separation (diastases) of the muscles along the front of the abdomen (the rectus abdominis muscles).
These two parallel sheets of muscles run from the rib cage to the pubic bone. As the uterus expands, these muscles sometimes separate along the center seam, and back pain can then become worse. Your doctor can tell whether the amount of separation is more than usual and may suggest ways to remedy the separation after your baby is born.
Pain in the lower abdomen during the second trimester is often related to the stretching of ligaments and muscles around the expanding uterus. Although this cause of abdominal pain doesn’t pose a threat to you or your baby, it’s important to report it to your doctor.
A fairly common cause of abdominal or groin pain in mid–pregnancy is stretching of the round ligament. Actually made of muscle cells, the round ligament is a cord–like structure that supports the uterus. Before pregnancy, the round ligament is less than a quarter of an inch thick. By the end of pregnancy, it has become longer, thicker and more taut. A sudden movement or reach can stretch the round ligament, causing a pulling or stabbing pang in your lower pelvic area or groin or a sharp cramp down your side. The discomfort usually lasts several minutes and then goes away.