What are the Measurements of Uterus During Pregnancy?

The uterus, also called the womb, is a vital organ in the female reproductive system. It is where a fertilized egg implants and the development of the baby occurs during pregnancy.

The uterus is normally small, like the size of an orange [1]. However, its size increases significantly during pregnancy to accommodate the growing baby. The changes in the uterus reverse gradually after the pregnancy ends.

In this article, we will explore the function of the uterus and see the measurements of uterus during pregnancy. This article also highlights the changes in the uterus after pregnancy.

How Uterus Functions?

The uterus is a pear-shaped, muscular organ located in the pelvis of a female anatomy [2]. It is small, typically about the size of a fist, and weighs around 50 to 60 grams in women who are not pregnant [3]. A normal size uterus has thick, stretchy walls that can expand significantly during pregnancy.

Before pregnancy, the uterus provides a favorable environment for the fertilized egg to implant. After the implantation, its function is to support the growth and development of a baby. The uterus also plays a role in menstruation by shedding its inner lining — endometrium — when a woman is not pregnant.

How the Uterus Prepares for Pregnancy

Pregnancy occurs when a fertilized egg implants into the inner lining of the uterus. The implantation does not occur until the inner uterine lining provides favorable conditions for the fertilized egg. To achieve this favorable condition, the female body constantly promotes the thickening and nourishment of the inner lining of the uterus during the menstrual cycle [3].

Following changes occur in the uterus to prepare it for potential pregnancy:

1. Thickening of the Endometrium

During the first part of the menstrual cycle, known as the follicular phase, the hormone estrogen helps thicken the uterine lining. After ovulation, the hormone progesterone takes over to continue this process. Working together, these hormones create a suitable environment in the uterus for the implantation of a fertilized egg [4].

2. Increased Blood Supply

The thickening of the uterus also involves the formation of new blood vessels. These blood vessels help the uterus receive more blood flow to support the early stages of pregnancy [4].

Fertilization occurs in the fallopian tube, not in the uterus itself. The fertilized egg travels down to the uterus, where it attaches to the uterine lining in a process called implantation. After implantation, the uterus begins to change in size to support the growing baby.

Measurements of Uterus During Pregnancy

The uterus grows rapidly along with the baby's growing size. Here is an overview of how uterus size changes in different phases of pregnancy:

1. First Trimester (Weeks 1–12)

During the first trimester, the uterus grows slightly but remains within the pelvis. By around 12 weeks, it is about the size of a grapefruit, and you may start to feel it above the pelvic bone, but it still fits into the pelvis [1].

2. Second Trimester (Weeks 13–26)

The uterus grows more noticeably in the second trimester and begins to move upward into the abdomen. By 20 weeks, the uterus reaches the level of the belly button. This is often when the baby bump becomes more visible in most women. The uterus pregnant stretches to about the size of a small melon during this time.

3. Third Trimester (Weeks 27–40)

The uterus grows to its largest size during the third trimester, stretching to accommodate the full-term baby. By the end of pregnancy, the uterus is about the size of a watermelon and extends from the pubic bone to the ribcage.

Doctors often measure the uterus's size using a method called fundal height measurement, which checks the distance from the fundus — top of the uterus — to the pubic bone [5]. These pregnancy uterus measurements help monitor the baby’s growth and ensure the pregnancy is progressing normally.

This exact fundal height in centimeters resembles the week of pregnancy. For example, if you are 20 weeks pregnant, the fundal height will be around 20 centimeters.

What Happens to the Uterus After Pregnancy?

After childbirth, the uterus returns to its pre-pregnancy size and shape with a process called involution [6]. Several milestones of this process are:

• In the first 24 hours after delivery, the uterus shrinks to about the size of a grapefruit.
• Over the next 6 to 8 weeks, it gradually reduces in size and returns to the pelvis.
• By the end of this period, the uterus is back to its pre-pregnancy size, although it may remain slightly larger in some women.

Breastfeeding can speed up uterine contractions because it stimulates the release of oxytocin, a hormone that stimulates uterine contractions.

Conclusion

The uterus is a critical organ in the female reproductive system, and it changes exponentially during pregnancy to support the growth of a baby. Before pregnancy, the uterus prepares itself for implantation by thickening its inner lining. After successful implantation, the embryo within the uterus starts to grow in size, which also stretches the size of the uterus. It is recommended to use prenatal supplements to venture through a normal pregnancy and meet the demands of extra nutrients required for changes in a female body.

The uterus can stretch from the size of an orange before pregnancy to the size of a watermelon by the end of the pregnancy. The uterus gradually returns to its pre-pregnancy size after childbirth. Regular checkups during pregnancy help ensure uterine health and overall well-being.

FAQs

1. Can the uterus return to its original size after pregnancy?

Yes, the uterus undergoes a process called involution to return to its pre-pregnancy size after childbirth. This is a gradual process and it takes around 6 to 8 weeks on average.

2. How breastfeeding impacts uterus size after pregnancy?

Breastfeeding stimulates the release of oxytocin hormone that has a positive influence on breastfeeding. Along with breastfeeding, oxytocin also stimulates uterine contractions which help the uterus in returning to its pre-pregnancy size after child birth.

3. What happens to the uterus during a C-section?

During a C-section, the uterus is surgically opened to deliver the baby. After delivery, it is carefully stitched back to allow proper healing. On average, it takes around 6 weeks for complete recovery from C-section.

Resources Used

1. Normal Uterus Size During Pregnancy. American Pregnancy Association. https://americanpregnancy.org/healthy-pregnancy/pregnancy-health-wellness/uterus-size-during-pregnancy/ 
2. Ameer, M. A., Fagan, S. E., Sosa-Stanley, J. N., & Peterson, D. C. (2022c, December 6). Anatomy, Abdomen and Pelvis: Uterus. StatPearls - NCBI Bookshelf. https://www.ncbi.nlm.nih.gov/books/NBK470297/ 
3. Professional, C. C. M. (2024j, May 1). Uterus. Cleveland Clinic. https://my.clevelandclinic.org/health/body/22467-uterus 
4. Bull, J. R., Rowland, S. P., Scherwitzl, E. B., Scherwitzl, R., Danielsson, K. G., & Harper, J. (2019). Real-world menstrual cycle characteristics of more than 600,000 menstrual cycles. Npj Digital Medicine, 2(1). https://doi.org/10.1038/s41746-019-0152-7 
5. What does fundal height measure in pregnancy? (n.d.). Mayo Clinic. https://www.mayoclinic.org/healthy-lifestyle/pregnancy-week-by-week/expert-answers/fundal-height/faq-20057962 
6. Deussen, A. R., Ashwood, P., Martis, R., Stewart, F., & Grzeskowiak, L. E. (2020). Relief of pain due to uterine cramping/involution after birth. Cochrane Library, 2020(10). https://doi.org/10.1002/14651858.cd004908.pub3