The uterus undergoes rapid changes during early pregnancy, including growth, increased blood flow, and softening of muscle fibers. These changes can cause common pregnancy symptoms such as frequent urination and cramping. The uterus also develops Braxton Hicks contractions and a mucus plug to protect the growing embryo. Abnormalities such as adhesions and fibroids may be discovered during pregnancy and require close monitoring.
The uterus undergoes rapid changes during early pregnancy. The changes include growth and increased blood flow to support the growing embryo. These changes are responsible for some of the most common pregnancy symptoms.
In women who are not and have never been pregnant, the uterus is 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 inserts into the pelvis and is protected by the pubic bone. By the end of pregnancy, it will have increased to approximately 1,000 times its normal size. The uterus is made up of smooth muscle tissue lined with glands.
One change to the uterus during early pregnancy is size. As early as the third week of pregnancy, or one week of gestation, the uterus begins to grow. This growth puts pressure on the bladder and causes more frequent urination. Uterine growth can also cause cramps, similar to those during menstruation. Severe cramping, especially when accompanied by back pain and increasingly profuse bleeding, can signal a miscarriage.
The uterus during early pregnancy gains more blood vessels. This allows for the passage of nourishment to the baby and placenta. Blood flow in existing blood vessels also increases. It also increases the elastic tissue in the uterine walls.
The muscle fibers that make up the uterus soften due to the action of the hormones estradiol and progesterone. This change of the uterus during early pregnancy allows for future growth. It also allows for the increased power of contraction later needed to expel the fetus.
The ligaments that support the uterus stretch to accommodate the growth. They also increase in diameter. This is sometimes felt as sharp pains in the lower abdomen.
The “practice” mild contractions, called Braxton Hicks contractions, start as early as the sixth week of pregnancy. This action of the uterus during early pregnancy may not be felt until much later in the pregnancy and can cause false labor. These contractions are important in preparing the uterine muscle for labor.
The glands of the uterus increase secretions. These form a mucus plug in the cervix, the opening to the uterus. This buildup of mucus prevents bacteria from entering the uterus from the vagina. It is expelled up to several weeks before labor.
Sometimes an unhealthy or abnormal uterus is discovered when pregnancy occurs. If there has been previous uterine surgery, adhesions may develop. This can present with extreme pain as the uterus grows. Fibroids, which are benign tumors of the uterus, can be discovered during an ultrasound examination. They usually don’t present problems during pregnancy, but they do need to be watched closely.
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