The size of the gland, as well as the size and appearance of the nipple and areola, varies greatly in different women; but under the stimulation of pregnancy the whole gland enlarges, including the connective tissue stroma.
About the fourth month a pale yellow secretion can be squeezed from the nipple. This is called colostrum. The pigmentation extends over a wider area and deepens in color, while the increased vascularity is shown by the appearance of the blue veins under the thin tender skin. Light pinkish lines sometimes radiate from the nipple. These are striæ and are more evident in blondes.
The milk comes into the breasts about the third day after labor, and normally continues to flow for six, to ten or twelve months.
Why the pregnancy and labor induce such marked mammary activity is not known, but the fact is patent.
The skin reacts both mechanically and biologically to the stimulus of pregnancy.
Fig. 25.—Striæ Gravidarum. (Edgar.)
Striæ Gravidarum.—Striæ gravidarum appear on the abdomen similar to those observed on the breasts and are due to the same cause—mechanical stretching. When fresh, they are pinkish in color and variable in length and breadth, but attain the greatest size below the umbilicus. Occasionally they extend to the thighs and buttocks.
After labor, they become pale, silvery, and scar-like and are called linea albicantes. They are sometimes found in other conditions than pregnancy, such as tumors or ascites.
Increased Pigmentation.—Pigmentation is not limited to the breasts. On the abdomen, a dark line will appear between the umbilicus and the pubes. This is the linea nigra, and it becomes most conspicuous in the latter half of pregnancy. In the groins, the axillæ, and over the genitals, the deposit is common, and sometimes patches appear on the face, either discrete or in coalescence, to form a continuous discoloration, called chloasma; or when extensive, the “mask of pregnancy.” The pigmentation is absorbed, or at least greatly diminished, after labor. The sebaceous and sweat glands are more active.