The uterus increases in size to make room for the growing baby. It increases in size from aproximately 6.5 cm. long, 4 cm. wide and 2.5 cm. deep to about 32 cm. long, 24 cm. wide and 22 cm. deep. Its weight increases from 50 gm to 1000 gm. The tremendous growth is due partly to the formation of new muscle fibers, but principally to the enlargement of the preexisting muscle fibers. The uterine wall thickens during the first few months of pregnancy, but thereafter it thins. Between the 3rd and 4th month of pregnancy the growing uterus rises out of the pelvis and can be felt above the symphysis pubis (pubic bone), rising progressively to reach the umbilicus (navel) about the 5th month. It then enlarges during the last half of pregnancy, squeezing up against the lower most part of the rib cage during the 9th month.
One of the first physical signs of pregnancy, softening of the cervix, may be apparent as early as 1 month after conception. The softening of the cervix is due to increased vascularity, edema and hyperplasia (increased cell formation) of the cervical glands. The glands of the cervical mucosa form a structure resembling a honeycomb. This so called "mucus plug" partially protects the uterus from contamination, and is expelled at the onset of (or during) labor. The vagina and external genital organs are being prepared for the passage of the fetus by becoming thicker, softer, and more vascular. This increase of blood supply gives a dark violet hue to the tissues. Vaginal secretions may be considerably increased, especially toward the end of the pregnancy.
The abdominal wall naturally enlarges to accommodate the size of the uterus. Pinkish steaks (striae gravidarum) are due to the stretching of the skin. The umbilicus (navel) is pushed outward until about the 7th month, then becomes flat, and later is raised above the surrounding tissue and may project.
One presumptive sign of pregnancy is that the breasts may become tender or tingle. After the 2nd month the breasts begin to become larger, firmer, and are still somewhat tender. As time goes on, the nipple and the pigmented area around it (the areola) become darker in color and the diameter gradually widens to reach 1-2 inches. The veins beneath the skin of the breast become more prominent. Little bumps raise on the areola, called Montgomery's tubercles. These are a normal sign of pregnancy. After the first few months a thin yellowish liquid may be expressed, or flow freely, from the nipples. This fluid is called colostrum, and is the first substance your baby obtains when suckled after birth. It is full of protective antibodies for your baby.
Stretch marks (striae gravidarum) often develop in the abdominal wall, breasts, the buttocks and the thighs. Certain pigmentary changes are also common, particularly the development of a dark line running from the navel to the pubic hairline, called "linea nigra". The oil and sweat glands become more active. The increased activity in the sweat glands produces an increase in perspiration, an alteration which is helpful in the elimination of waste material.