Physiological changes in the mother, third trimester

The vagina progressively stretches during pregnancy to prepare for delivery. At the end of pregnancy there is an increase in vaginal discharge with a thick white appearance, which plays an important role in the control of vaginal flora. The glands of the cervix increase and in the third trimester they secrete a large amount of mucus that accumulates in the cervical canal and forms the mucous plug.

The uterus receives a large amount of blood, which goes from 1% of the total blood volume without pregnancy to 20% at term.

In the third trimester, the fetus' demand for calcium and phosphorous increases for the formation of its bones, so they must be increased in the diet.

There is swelling or edema in the legs and feet because the compression of the uterus on the vena cava hinders the venous return, this is more pronounced at the end of the day and improves at rest. This edema can occur in the hands, producing in some cases carpal tunnel syndrome, a sensation of pain or numbness in the hands, more frequent at night or in the morning, due to compression of the median nerve. Eyelid edema also appears on the face, lips giving the typical face of a pregnant woman.

This pressure of the uterus on the venous return also produces varicose veins, which depend on the predisposition of each woman, due to the distension of the vein walls and the increase in blood volume. They usually appear on the lower extremities and are also common on the vulva.

Hemorrhoids are aggravated by the difficulty in the venous return, so pain, itching or stinging and even bleeding may appear.

Itching is also common, that is, itching on the skin of which the cause is unknown, but probably due to stretching of the skin. The black line is more obvious and hair may appear on the abdomen.

The increased volume of the abdomen causes compression of the rib cage, which can cause a feeling of suffocation. Breathing is shallower and the usual composition of blood gases varies. When the rib cage is also distended, rib pain or pain at the level of the intercostal muscles may appear, due to the compression of the intercostal nerves, this is "intercostal neuritis".

Back pain is accentuated, if it only occurs at the lumbar level it is called low back pain, but if the pain radiates along the buttock, thigh and leg until it reaches the foot, it is sciatic pain due to compression of the sciatic nerve.

During the third trimester, Braxton-Hicks contractions appear, the gut is noticeable that hardens, without regularity and more frequently when walking or exercising. Pelvic discomfort and vaginal punctures and cramps are also common.