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What Happens to the Uterus during Early Pregnancy?

Bobbie Fredericks
Bobbie Fredericks

The uterus undergoes rapid changes during early pregnancy. Changes include growth and increased blood flow to support the growing embryo. These changes are responsible for some of the common early pregnancy symptoms.

In women who are not and have never been pregnant, the uterus is about the size of a small pear. The uterus is slightly larger in women who have been pregnant in the past or are currently pregnant. It fits into the pelvis, and is protected by the pubic bone. By the end of pregnancy, it will have increased to about 1,000 times its usual size. The uterus is made of smooth muscle tissue lined with glands.

Uterine growth may cause cramping during pregnancy.
Uterine growth may cause cramping during pregnancy.

One change to the uterus during early pregnancy is size. As early as the third week of pregnancy, or one week gestation, the uterus begins to grow. This growth puts pressure on the bladder and causes more frequent urination. Uterine growth may also cause cramping, similar to that during a menstrual period. Severe cramping, especially if accompanied by back pain and increasingly heavy bleeding, may signal a miscarriage.

The uterus during early pregnancy gains more blood vessels. This allows nourishment to pass to the baby and to the placenta. Blood flow in the existing blood vessels increases as well. The elastic tissue in the uterine walls also increases.

The uterus is part of the female reproductive system.
The uterus is part of the female reproductive system.

Muscle fibers that make up the uterus soften due to actions of the hormones estradiol and progesterone. This change of the uterus during early pregnancy allows for future growth. It also allows for the greater contracting power later needed to expel the fetus.

Ligaments that support the uterus stretch to accommodate growth. They also increase in diameter. This is sometimes felt as sharp pains in the lower abdomen.

By the end of pregnancy, the uterus will have increased to about 1,000 times its usual size.
By the end of pregnancy, the uterus will have increased to about 1,000 times its usual size.

Mild "practice" contractions, called Braxton Hicks contractions, start as early as the sixth week of pregnancy. This action of the uterus during early pregnancy can not be felt until much later in pregnancy, and may cause false labor. These contractions are important for preparing the uterine muscle for labor.

The glands of the uterus increase secretions. These form a mucus plug in the cervix, the opening of the uterus. This build up of mucus prevents bacteria from entering the uterus from the vagina. It is expelled up to several weeks preceding labor.

A uterus may be examined with an ultrasound during early pregnancy.
A uterus may be examined with an ultrasound during early pregnancy.

Sometimes an unhealthy or abnormal uterus is discovered when a pregnancy occurs. If there has been previous uterine surgery, adhesions may develop. This may present with extreme pain as the uterus grows. Fibroids, which are benign tumors of the uterus, may be discovered during ultrasound examination. They usually do not present problems during pregnancy, but need to be closely watched.

Discussion Comments

Federlink

There are lots of changes in the uterus during the first trimester, which can be stressful for a new mother. Most obstetricians are more than willing to perform a transvaginal ultrasound if a patient experiences bleeding during early pregnancy, to help confirm a miscarriage or to reassure a patient.

RationallyMellow

I'm having bleeding and cramping, and have been for several days. This is my first pregnancy, and I don't want to call the doctor unnecessarily. Does cramping during early pregnancy automatically signal a miscarriage?

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    • Uterine growth may cause cramping during pregnancy.
      By: georgerudy
      Uterine growth may cause cramping during pregnancy.
    • The uterus is part of the female reproductive system.
      By: fixer00
      The uterus is part of the female reproductive system.
    • By the end of pregnancy, the uterus will have increased to about 1,000 times its usual size.
      By: Valua Vitaly
      By the end of pregnancy, the uterus will have increased to about 1,000 times its usual size.
    • A uterus may be examined with an ultrasound during early pregnancy.
      By: photographmd
      A uterus may be examined with an ultrasound during early pregnancy.