Changes of Uterus During Pregnancy

The uterus or the womb is an organ of the female reproductive system. This hollow muscular organ is responsible for the development of the embryo and fetus. The uterus is an incredible distensible organ. In the beginning, it could be around the size of a fist, but it can expand enough to accommodate a full term baby. It consists of several strong muscles that help it push a full term baby out through the vagina. Keep reading to find out more about the changes in the uterus during pregnancy.

Size Changes of Uterus During Pregnancy

Before pregnancy, the uterus is pear-shaped and about 3 cm thick, 4.5 cm wide and 7.6 cm long. But it is extremely accommodating and expands in size in a systematic way as per the size of a growing baby. Here is more about it.

1. First Trimester

When you are 12 weeks pregnant, the size of your uterus would be similar to the size of a grapefruit. It slowly grows up and out of your pelvis during pregnancy. Your uterus will start expanding early in pregnancy if you are carrying twins or multiples. Your gynecologist can feel your uterus during pregnancy even by touching your belly.

2. Second Trimester

Your uterus will grow to the size of a papaya during the second trimester. It will come out of the pelvis and be midway between your breasts and the navel. As it keeps growing, it starts pushing your organs and moves them out of their usual places. It will also put pressure on surrounding ligaments and muscles. That's why you are more likely to experience pains and aches during your second trimester.

During 18 to 20 weeks of pregnancy, your doctor will check the distance between the top of your uterus (called the fundus) and your pubic bone. This is called the fundal height and it helps a lot in determining how long you have been pregnant. For example, if your fundal height is 32cm, you are 32 weeks pregnant. But for first pregnancy, this measurement may be larger.

Moreover, the size of your uterus during pregnancy will help your doctor know if everything is progressing normally. You may experience some pregnancy complications if your uterus size at a particular time during pregnancy is too big or too small. In this case, additional tests are needed to make sure everything is all right.

3. Third Trimester

Your uterus will be about the size of a watermelon in your third trimester. Your uterus will extend to the bottom of your rib cage by the time you reach full term. Your baby will drop into your pelvis when you are ready for labor.

4. After Birth

Your uterus will return to its normal (pre-pregnancy) size after delivery. The process of uterus returning to its original size and position is called involution. The uterus usually returns to its normal position in about 6 weeks after delivery.

What Happens Inside the Uterus During Pregnancy?

Besides, the changes in size, there are many changes happen in the uterus during pregnancy. Here are some of the main changes:

1. Corpus Luteum Develops

The corpus luteum is a structure that develops immediately after the fertilization of an egg. It surrounds the growing embryo and releases the main pregnancy hormones like progesterone. It is due to progesterone that your uterus does not contract as it normally would during your regular menstrual cycles. The corpus luteum is also responsible for the growth of the lining around the walls of the uterus.

2. Placenta Forms

After the implantation of the embryo in the uterine wall, tiny finger-like projections develop. The process usually takes place about 6-12 days after fertilization. The projections grow and become the placenta, which nourishes and support the growing embryo. The placenta produces both progesterone and estrogen, which encourage further changes in the size and position of the uterus.

3. Blood Vessels Enlarge

After four weeks into pregnancy, the blood vessels in the uterine lining will grow and enlarge, thickening the uterine lining. This helps support and nourish the growing embryo.

4. Cervix Softens

The opening at the bottom of your uterus is called the cervix, which starts to change its texture and color around four weeks of pregnancy. It will look bluish after week five and a mucous plug will develop about five weeks after fertilization that will secure the uterus and protect it from outside contamination.

5. Lower Segment Changes During Pregnancy

By about 24 weeks of pregnancy, your myometrium muscles in the uterus will begin to stretch upwards, making the upper part of your uterus a bit thicker and leaving relatively thinner layers of muscle below, known as lower segment. This lower segment separates the upper segment from the cervix, and it absorbs the cervix when it begins to dilate during labor.

6. Ligaments Changes During Pregnancy

The uterus will tilt towards the right side with the progression of pregnancy. The ligaments support, anchor and stabilize the uterus, and the ligaments can be stretched during pregnancy. But sometimes these stretches may cause sharp pains within the groin. The sharp pain is usually the outcome of coughing, sneezing or doing anything suddenly.

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