A normal human backbone is slightly recurved--it bows naturally outward near the bottom of the ribcage, bows in at the neck and small of the back, and then back out again at the top and bottom ends of the spine. This shape helps maximize spinal elasticity and minimize the potential for injury while supporting muscles and allowing for two-legged movement under normal circumstances. The extra weight of a baby in the lower portion of a woman's abdomen changes the curvature of her spine significantly, which can stress muscles of the lower back. As the back is thrown out of its accustomed balance, upper back and shoulder muscles work to compensate, which in turn can cause neck pain. In their book, "What To Expect When You're Expecting," authors Heidi Murkoff and Sharon Mazel suggest that tight neck muscles benefit from gentle stretching. They recommend slowly tilting the head from side to side and back and forth to ease pain.
Lack of Exercise
Early in pregnancy, women often experience extreme fatigue. The second trimester brings a burst of energy for many, but increased weight and decreased mobility in the last months of pregnancy find many women avoiding the gym. This can result in both tight and atrophying muscles, particularly in the upper back. In his book, "What You Didn't Think to Ask Your Obstetrician," Dr. Raymond Poliakin notes that changing hormone levels soften joints, meaning that ligaments do less--and therefore muscles must do more--to hold those joints in place. If muscles atrophy, joints may become loose, and compress nerves, leading to pain. Particularly for women who spend long periods of time reading or on the computer, these factors, coupled with a hunched posture that people often assume while typing can create and exacerbate neck pain.
Even women with the best of intentions who find the time to hit the gym regularly during pregnancy can find themselves struggling with neck pain. Changes in body habits make it difficult to anticipate which parts of a typical workout routine will be helpful and which exercises might hurt a pregnant body, in which weight is distributed differently. Women who have back or neck pain and who have been working out regularly may have injured the neck as a product of those workouts, notes Discovery Health online. In particular, abdominal exercises--which some pregnant women undertake to prepare for labor--run the risk of hurting the back and neck. Since it's quite a bit harder to perform sit-ups with a pregnant belly, pregnant women tend to lead with the head, which can strain the neck and lead to pain. It's worth noting that most physicians don't recommend exercises that require lying on the back for a long period of time after the second trimester, but even early in pregnancy, women should take care to avoid neck injury while working out.