What Causes Lower Back Pain in Pregnancy?

Pregnant women pore over books, magazines, and other resources to help themselves learn everything they can about their changing bodies and growing babies. But many feel left in the dark when it comes to figuring out what causes a very common and extremely disruptive symptom of pregnancy: lower back pain. Experts generally put the causes of pregnancy-related lower back pain into three major categories: biomechanics, hormones, and stress.

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Biomechanics

Biomechanics refers to the ways your body holds itself (like posture) and moves (like joints), and is the main cause of pregnancy-related back pain. Because a pregnant body is asked to carry an additional -- and significant -- physical load, even a healthy body can be tipped out of balance, even if an expectant mom stays within the recommended 25-to-35-pound weight gain as the pregnancy progresses.

Damla Karsan Dryden, M.D., an ob-gyn at Texas Children's Pavilion for Women in Houston, summarizes the lumbar spine's challenges and the related postural problems (such as slumped shoulders or collapsed chests) this way: "As the baby grows during pregnancy, the mother's center of gravity shifts forward, placing more strain on the lower back." Simply put, the biomechanics of pregnancy involve the growth of the belly away from the body, a process that pulls the lumbar spine (the flexible vertebrae that compose the lower back) forward along with it. The result of this extra pressure is often a lordosis, or an exaggeration of the lumbar spine's natural inward curve. Lordosis can result in the vertebrae compressing and the lower back muscles shortening, both of which can cause pain.

The biomechanics of lower back pain during pregnancy involve the bones, joints, muscles, ligaments, and sometimes nerves. Ligaments loosen from pregnancy hormones and core muscles have to work harder to protect the spine and pelvis. If these muscles are weak or firing incorrectly, the weight-bearing joints (called sacroiliac joints) that connect a bone (called the sacrum) in your lower spine with your hip bones are particularly at risk of becoming injured or inflamed. The resulting joint pain can radiate through the buttocks and down the legs. Although some pregnant women may complain of sciatica (a shooting pain that radiates from the buttocks down the legs) during pregnancy, they actually may be experiencing something else entirely. Colleen Fitzgerald, M.D., the medical director of the Chronic Pelvic Pain Program for the Loyola University Health System in Maywood, Illinois, says, "True sciatic nerve problems occur in less than one percent of all pregnant patients. It is more likely that the patient has pelvic girdle pain of the sacroiliac joint region."

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Hormones

Hormones are the second main cause of pregnancy-related lower back pain. During the first half of pregnancy, your body's levels of progesterone (a hormone that stimulates the uterus) surge, helping to loosen and relax the ligaments and tissues that are going to stretch as the pregnancy progresses. During the second half of pregnancy, the brain releases another hormone, called relaxin, to help the ligaments between the muscles of your pelvic girdle open more to make room for the baby to be born. The hormones have an important job: "The pelvis is three bones glued together, " explains Adam Romoff, M.D., an associate chairman of obstetrics and gynecology at Lenox Hill Hospital in New York City. "These hormones loosen the glue."

The hormones aren't restricted to the pelvic area during pregnancy; they circulate throughout your entire body. As a result, all that loosening and opening causes instability in all your joints, leaving them prone to painfully imbalanced alignment or even injury -- and your lower back is one of the most vulnerable spots to be affected.

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Stress

The third cause of lower back pain in pregnancy is also a cause of lower back pain in your everyday life -- stress. "Having a baby is, for a lot of women, stressful, especially if it's their first and they don't know what to expect," says Robert Kum, D.C., a chiropractor in Arlington, Massachusetts, who has treated hundreds of pregnant women. "And we all know what stress can do to the body -- it increases tightness and muscle pain." Just being aware that stress is causing pain in your body can be a liberating insight. Dr. Kum recommends that women do whatever they can to manage stress by staying comfortable. Meditation, yoga, enough sleep, and good emotional support can all help. "Pregnancy is a journey," Dr. Kum says, and some of the stops along the way are more pleasant than others. But when it comes to back pain, it's good to remember that relief is possible, and perhaps just as important, "you're not alone."

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Holly Lebowitz Rossi writes the Parents News Now blog for Parents.com, and she is the co-author, with yoga teacher Liz Owen, of Yoga for a Healthy Lower Back: A Practical Guide to Developing Strength and Relieving Pain.

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