This line is called linea nigra, and it's totally common during pregnancy. The linea nigra is the result of fluctuating hormones. One theory is that they cause your body to make more than the usual amount of melanin, a compound responsible for giving your skin pigment, and this extra pigmentation shows up as a dark line stretching from the belly button to the top of the pubic hair. Women of all different skin colors are affected, although the line can be more pronounced in women with fair skin. To minimize the discoloration, keep your belly covered when you head to the beach, and don't use tanning beds (which you should be avoiding anyway). Rest assured that after your baby is born the line will disappear eventually. Most women report that their linea nigra fades about six to 12 months after they deliver.