Which sign is commonly observed at the 12-week mark during a physical examination of a pregnant woman?

Chadwick's sign is characterized by the bluish discoloration of the vaginal mucosa and cervix, which occurs as a result of increased blood flow and vascular congestion in these areas during early pregnancy. This sign is typically observable around the 12-week mark, aligning with the physiological changes that occur as the body adjusts to pregnancy.

Recognizing Chadwick's sign during a physical examination is vital as it can affirm the presence of pregnancy. The increased vascularity and subsequent change in color is a reliable indicator for healthcare providers to note.

In contrast, edema of the lower extremities is more commonly seen in the later stages of pregnancy due to increased fluid retention and pressure from the growing uterus. Fundal height at the umbilicus is usually noted around 20 weeks of gestation, not at 12 weeks, as it takes time for the uterus to grow and move above the pubic symphysis. Increased blood pressure is not a typical finding in early pregnancy; instead, blood pressure may actually decrease in the first trimester due to the effects of progesterone and reduced vascular resistance.