Sudden lack of breast swelling and pain in the fifth week of pregnancy may be a normal physiological phenomenon, or it may be the cause of poor embryonic development or embryonic arrest. Elevated hormone levels after pregnancy will cause symptoms such as breast enlargement, deepening of areola coloring and breast swelling and pain, and some pregnant women may remain unresponsive, which is also a normal physiological phenomenon. However, when the localized swelling and pain in the breasts at the fifth week of pregnancy suddenly decreases or disappears, there is a possibility of embryonic underdevelopment or embryonic failure, and ultrasonography, blood HCG (human chorionic gonadotropin) and progesterone tests need to be performed to find out about the development of the embryo. Most pregnant women will also experience early pregnancy reactions such as nausea, vomiting, anorexia, etc. They need to pay attention to proper rest, avoid coitus and take folic acid as prescribed by the doctor. When the symptoms of early pregnancy suddenly disappear, or the presence of abdominal pain, vaginal bleeding and other conditions need to go to the hospital in time to consult, clear causes and then actively deal with. Therefore, when the breasts suddenly stop swelling and aching during the fifth week of pregnancy, you need to go to the hospital and follow the doctor’s instructions to carry out ultrasound examination to find out the cause and actively deal with it.