Physical Changes Before Labor

What about the mother? What changes do you experience in preparation for the birth? The changes that come with pregnancy affect not only the baby, the uterus, and the placenta, but also the mother's entire body, her mind, and her emotions.

For example, your breasts began changing as soon as you became pregnant. You may have noticed some breast changes (tenderness, tingling sensations, and feelings of heaviness) very early, even before you knew you were pregnant. These changes indicate your body is beginning to get ready for breast-feeding. By late pregnancy, you may notice more veins in your breasts, indicating the increased blood supply in the area. You may also notice your breasts are somewhat larger than they were before, and the areolae (the circles around your nipples) may have darkened. Inside the breasts, the milk-producing glands have grown larger. They even begin producing a substance called colostrum, which enables you to breast-feed as soon as the baby is born.

Other parts of your body also change in preparation for the birth. For example, the ligaments begin to soften. This is particularly helpful in the pelvis, through which the baby passes during birth. Flexible ligaments allow the pelvis to enlarge somewhat, making more room for the baby. These changes sometimes cause shooting pains in your hips, stiffness in the lower part of your back, or soreness in the front joint of your pelvis (the symphysis pubis) and the sacroiliac joints. Although inconvenient now, these changes really are a benefit during the birth process.

Like many women, you may experience heartburn and constipation, partly due to slowing of digestion and partly due to the size of the uterus, which crowds your stomach and intestines and causes you to burp up acid and have trouble moving your bowels. Despite these discomforts, there are benefits. Your body is able to absorb more nutrients from your digestive tract because of this slowing of digestion.

Your uterus undergoes vast changes in the last trimester of pregnancy. Obviously, it becomes much larger. It must accommodate the growing baby, the placenta (which weighs about one sixth of the baby's weight), and about one quart of amniotic fluid. As your uterus stretches around the growing baby inside, it becomes more sensitive. If you sneeze or bump your abdomen, your uterus often contracts immediately afterward. It is very sensitive to sudden pressure. Sometimes, while you rest, your uterus spontaneously contracts several times in a rhythm. More than one woman has wondered if she is in labor when this kind of contraction pattern occurs. These contractions, called Braxton Hicks contractions, are an indication the uterus has become more sensitive to the circulating oxytocin.

While Braxton Hicks contractions are not labor, they probably cause changes in your cervix that prepare it for labor. These changes include ripening (softening), effacement (thinning or shortening), and some dilation (opening) of the cervix prior to the onset of labor. Although you are probably unaware of it, the cervix, which is usually quite firm and thick, becomes soft and thin before labor begins. A ripe, thin cervix opens up much more easily than an unripe, thick cervix. The amount of ripening and thinning can be determined only with a vaginal examination. Effacement is measured as a percentage. For example, if your cervix is 25 percent effaced, it is 25 percent thinner, or shorter, than usual. (The cervix is usually about three to four centimeters long. Twenty-five percent effaced means 21/4 to 3 centimeters remain.) At 100 percent effacement, the cervix is paper thin.

Your cervix opens slightly before you go into labor. Referred to as dilation, this process is measured by feeling the circular rim of the cervix and estimating (in centimeters) the diameter of the opening. Many women are one or two centimeters dilated before they are aware of any signs of labor. During labor your cervix continues dilating to about ten centimeters (a circle about four inches across).
This preliminary work of the uterus in preparation for labor is thought to be controlled by the changing hormone production in the placenta, the baby, and the mother.