Thanks for the query.
The blue veins over the breasts seen few days before the onset os menses along with soreness of breasts are a part of premenstrual syndrome or PMS when the breasts tend to get swollen and the veins shine through the thin white skin. These are due to lowering progesterone levels preparing for a withdrawal bleed in form of menses in next few days. This phenomenon is normal and shouldn't be associated with pregnancy. However, it is always better to rule out pregnancy if suspected with a serum beta hCG test.
I hope I have answered your query in detail.
Wishing you good health.
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