The swelling of the stomach like a ball a week before menstruation is mainly related to water and sodium retention, pelvic congestion and so on. 1. Sodium retention: Before menstruation, such as the week before menstruation, with the change of estrogen and progesterone in the body, it is easy to cause sodium retention, resulting in mild swelling of the whole body, and even discomfort such as swelling of the stomach like a ball, distension and pain. But after the menstruation, with sex hormone changes, the above phenomenon will naturally ease; 2, pelvic congestion: the week before the menstruation body prostaglandin secretion will increase significantly, easily cause pelvic congestion. The pelvic congestion easily affects the normal gastrointestinal function of women, causing abdominal distention, even the stomach swells like a ball, often accompanied by lower abdominal pain. This condition generally belongs to the range of menstrual syndrome, usually after the period can be self-relieved; 3, other causes: may be unrelated to menstruation, such as eating spicy food a week before menstruation, or abdominal cold, causing gastrointestinal dysfunction, may cause abdominal distension, abdominal pain, or even stomach distension like a ball. Most of them do not need special treatment. Pay attention to adjusting the diet structure, eat less ingredients that are not easy to digest, and take probiotics such as Bifidobacterium tetrasporium tablets to regulate them if necessary. During menstruation, you need to pay attention to rest and keep warm, not to eat cold food and moderate exercise. Also pay attention to the health care before and after the period, can effectively improve the quality of life during the period.