How Does The Uterus Change During The 3 Trimesters Of Pregnancy?

The most used example for this progression is comparing the uterus with four fruits as follows:

Orange (pre-pregnancy)- grapefruit (first trimester) – papaya (second trimester) – watermelon (third trimester).

The size of your uterus in the course of pregnancy will help your specialist know whether everything is advancing as per the rule. You may encounter some pregnancy issues if your uterus size at a specific time amidst pregnancy is too large or too small. The size of the uterus determines the fontal length (distance between the top of the uterus to the pubic bone).

 The Normal Size Of The Uterus (Before Pregnancy)

Before pregnancy, a normal-sized uterus will be 7.6cm X 4.5cm X 3cm (length, width, and thickness respectively). For your convenience, you can imagine the pre-pregnancy uterus as big as an orange or more often as big as your fist. It’s quite surprising to know how the uterus change during the 3 trimesters of pregnancy.

What Happens To The Uterus When A Woman Gets Pregnant?

The major changes that occur in women’s bodies when they get pregnant happen inside the uterus. Then only all the other parts start to undergo pregnancy changes.

• The first change is to prevent the tendency of the uterine wall to contract and then shed the thickened uterine lining. This occurs as in the case of during the monthly periods and hence stops when you become pregnant. For this, as soon as the fertilized egg is implanted in the thickened wall of the uterus, a structure called corpus luteum develops and surrounds the growing embryo. Corpus luteum secretes progesterone, which is one of the crucial pregnancy hormones, which puts down the tendency of the uterus to contract
• Around twelve days after the fertilized egg implants into the uterine wall, tiny finger-like projections develop. These projections, in due course of time, become the placenta. The placenta produces both estrogen and progesterone (pregnancy hormones) which are responsible for further changes in the uterus throughout the pregnancy
• The blood vessels in the uterine wall will begin to expand roughly around one to two weeks after fertilization. These blood vessels make the uterine wall become thicker, which is significant for the nourishment and growth of the embryo
• Around three weeks after fertilization, that is around the fifth week of the pregnancy the uterus grows bigger than its initial size. Even though it can’t be felt or seen from our side the urinary bladder starts to know the pressure the uterus put on it as the uterus starts to lean on the bladder. The result – is increased urination

Changes That Happen To The Uterus In The First Trimester

The changes of the uterus depend on the type of pregnancy. During multiple pregnancies, obviously, the growth and stretching of the uterus will be sooner than that in normal pregnancy with a single baby.

• The uterus starts to move out of the pelvic cavity even though the baby is too small and could still be fit within it
• The uterus will grow from the size of an orange to a size of a grapefruit
• By the 12th week of the pregnancy, the uterus moves out of the pelvic cavity

What Changes Happen To The Uterus In The Second Trimester?

The uterus expands more and becomes heavier as it is accommodating a baby who grows day by day.

• It can no longer fit in the pelvis
• The uterus moves and takes a position between the navel and breasts
• It starts to push other internal organs away from their usual positions. The pressure from the uterus can push your belly button and it may stick out towards the end of the second trimester
• The size of the uterus influences in determining the fontal length. The doctor usually measures the fontal length during the second trimester of the pregnancy to confirm how long (weeks) the pregnancy progressed
• The myometrium muscle in the uterus starts to stretch upwards
• The upper part of the uterus become relatively thicker
• The thinner lower segment, which is comparatively thin separates the upper thicker part of the uterus from the cervix below
• This lower segment, being thinner, absorbs the cervix once it starts to dilate during the labor
• The lower segment has less supply of blood when compared with the upper segment. Thus, the cesareans are always conducted by cutting the lower segment with less blood supply to avoid the chances of excessive bleeding

What Changes Happen To The Uterus In The Third Trimester?

• During the third trimester, the uterus will start to cease its growth.
• The uterus leans towards the right side. This is made possible by the ligaments which hold the uterus. The ligament act as the anchor. It enables the stabilization of the uterus as the baby grows fast during the last weeks of the pregnancy. It also helps the movement of the baby inside the uterus.
• Towards the end of the pregnancy, the uterus will be fully enlarged. It will extend from the pubic area towards the lower part of the rib cage.

The uterus is a female’s most vital reproductive organ. Hence its growth as the pregnancy progresses holds a huge significance. And it is quite amazing to know how the uterus change during the 3 trimesters of pregnancy.