If you have ankylosing spondylitis, you have about an equal chance of having your disease improve, worsen or stay the same during the course of your pregnancy, according to a 1998 study of 939 women with the disease. The study also found that women with peripheral arthritis (that is, arthritis in joints away from the spine) were more likely to experience improvement during pregnancy than those whose arthritis was confined to their spine.

If your disease was active when you became pregnant, it is more likely to flare shortly after you deliver your baby. As many as 60 percent of women had a flare of their disease after delivery, the study found.  

Having ankylosing spondylitis is unlikely to affect your baby; however, it can affect your baby’s delivery.  Spinal inflammation or fusion may make it difficult or inadvisable for a doctor to perform an epidural, a procedure in which pain medication is injected between the vertebrae directly into the outer layer of the spinal canal; it is the most common form of pain control used in both vaginal and Cesearan births. Women with severe spinal involvement should discuss alternative pain-relief methods with their doctors before delivery. If a C-section is a necessity – as it often is in women with ankylosing spondylitis – you may need to have general anesthesia.

 “Any form of arthritis that involves the hips may make vaginal delivery difficult,” says Michael Lockshin, MD, professor of medicine and OB/GYN at Weill Cornell Medical College and director of Volcker Center for Women and Rheumatic Diseases at the Hospital for Special Surgery in New York. “The biggest problem is that you have to be able to spread your legs fairly wide. A baby is a pretty big package to get through there.” For that reason, women with arthritis – even if their disease is inactive and their pregnancy uncomplicated – may be more likely to deliver by C-section.