There is no obvious difference between the breast swelling that occurs during menstruation and early pregnancy in terms of self-perception, but there is a difference in terms of the mechanism of its occurrence, the time of its occurrence and the changes in the breasts. Menstruation is the common name for menstruation, and the breast swelling that occurs during menstruation is mainly due to the expansion of the mammary ducts, congestion, and interstitial edema of the breasts, which is often seen in the pre-menstrual period, accompanied by pain, and is generally not accompanied by obvious changes in the breasts, areolas, and nipples. On the other hand, breast distension that occurs during early pregnancy, in addition to the effect of estrogen levels, there is also a large amount of progesterone, often occurring after the delay of menstruation, often accompanied by breast enlargement, congestion is obvious. Both menstruation and early pregnancy can lead to breast swelling, so it is impossible to tell what causes it simply from the clinical manifestation of breast swelling, that is to say, you can’t judge whether or not you are pregnant from the clinical symptom of breast swelling. If you can’t tell whether it’s due to menstruation or early pregnancy, it’s recommended that you go to the hospital and have a checkup.