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You may not have heard of ankylosing spondylitis before, as it strikes no more than 14 out of every 1,000 people and it is 2-3 times more common in men than in women. Since it often strikes young people before age 30, and nearly all the time before 45 years of age, ankylosing spondylitis can produce symptoms during pregnancy, when your body is under stress. Ankylosing spondylitis is a long-lasting (chronic) disease involving the skeletal system. It causes arthritis in the pelvis and back, meaning inflammation of the vertebrae of the spine and of the connections between the lower spine and the pelvis. Over time, the vertebral inflammation destroys vertebrae and fuses the sacral spine and the iliac bones of the pelvis. If you suffer from ankylosing spondylitis, you experience increasingly severe back pain and progressive stiffness of the spine. Symptoms are often worse in the morning and improve during and after exercise. The stiffening is related to vertebral bones fusing together. Over time, this process deforms the spine, which interferes with your posture and activities, including walking. If you also become pregnant, because of the growing womb (which often produces back pain even in normal pregnancies), the deformity of your back increases, while stiffness and pain can worsen. Ankylosing spondylitis may thus flare up during pregnancy. Alternatively, it can show up for the first time during pregnancy, or it can exacerbate back and pelvic pain and normally develops toward the end of pregnancy.
If your primary care physician suspects ankylosing spondylitis, or some other inflammatory condition, they may order a few basic laboratory tests, such as erythrocyte sedimentation rate (ESR) or C-reactive protein. They may also order X-rays of your spine or magnetic resonance imaging (MRI) scan of your pelvis. If you are pregnant and thus seeing an obstetrician on a regular basis, the obstetrician may take the role of the primary care physician, and order these tests. During the office visit, the physician will also perform a physical examination with emphasis on the musculoskeletal system. They will examine your posture and the natural curvature of your lower and upper back (called “lumbar lordosis” and “thoracic kyphosis”). They also will assess the range of motion and flexibility of various joints.
After initial evaluation, your doctor will probably send you to a rheumatologist, who will continue the diagnostic workup, especially with additional laboratory testing and imaging. Some tests will be for the sake of ruling out other conditions that can look similar to ankylosing spondylitis. These conditions include mechanical lower back pain, lumbar spinal stenosis (narrowing of the canal inside the spine that encloses and protects the spinal cord), and rheumatoid arthritis. One of the most important tests is called “HLA-B27” and it allows the rheumatologist to distinguish between ankylosing spondylitis and other conditions.
There are two main categories of drugs that are effective against ankylosis spondylitis: non-steroidal anti-inflammatory drugs (NSAIDs) and tumor necrosis inhibitors. NSAIDs include ibuprofen, naproxen, and various others. There is some concern that NSAIDs in high doses early in pregnancy may cause spontaneous abortion (miscarriage) and possibly birth defects. Much more of a concern (due to stronger scientific evidence) is that late in pregnancy (after 30 weeks gestation), NSAIDs can cause premature closure of the ductus arteriosus; this is a passageway that allows blood to flow from the pulmonary artery to the aorta during fetal life, so that oxygenated blood can reach fetal tissues. NSAIDs are considered to be fairly safe in mothers who are nursing.
As for tumor necrosis inhibitors, there is some evidence that, if taken in late pregnancy, they may interfere with the immune system of the neonate, but more studies are needed to know if they are harmful. Tumor necrosis factor inhibitors also may enter breaskmilk, but this too is based on limited studies. However, if you are concerned about unknown risks, simply do not breastfeed, as infants on baby formula probably do just as well as infants who are breastfed. Possible benefits from breastfeeding are hypothetical, and not actually proven.
One important issue connected with having ankylosing spondylitis when you are pregnant is that you may have limited range of motion in the lower back and pelvic joints. This means that you may not be able to open your legs easily, and so your obstetrician will likely perform a cesarean section.