Pregnant Belly Stages: Size & Shape Progression

By OBGYN Dr. Kenosha Gleaton

Today we’re going to discuss the stages of pregnancy, especially the physical changes you may or may not notice along the way. I’ve said it (many times) before and I’ll say it again— every pregnancy is different. This doesn’t just include someone’s fertility journey, but their symptoms, their expectations, their emotions, the childbirth and postpartum experience, and especially the way their body changes during pregnancy. Keep this in mind as you read on. 

Factors Influencing Belly Size and Shape

Whether you’re pregnant for the first time or you’ve been around the block a few times, it’s normal to have questions about the way your body is changing to accommodate your baby. We know that every body is different, especially during pregnancy, but what actually influences belly size and shape? There are a few factors [1]:

• Carrying multiples: If you’ve been pregnant with one baby and have been told you “must be carrying twins!” you might be rolling your eyes (and rightfully so). The truth is that carrying multiples may lead to your bump showing earlier on, growing faster, and resulting in more weight gain than a singleton pregnancy. This is all normal and healthy in order to support the babies. On the flip side, a big bump early on does not guarantee that someone is carrying multiples. 
• Previous pregnancies: If you’ve been pregnant before and have carried to term or close to term, your body remembers how to expand and accommodate your pregnancy accordingly. Those who have had a bump before may end up showing sooner and carrying lower as a result of previously stretched ligaments and muscles. 
• Your frame: If someone is naturally petite, a pregnant belly may be a bit more obvious earlier on. Those with an average to larger frame may not have as noticeable of a bump until sometime during the second trimester. 
• Muscle tone: Your abdominal muscles play a big role in your pregnancy belly. People with defined or strong abdominal muscles may carry higher and closer, meaning their bump may not extend out quite as far. Those with weaker muscles may see the opposite effect- carrying low and further from the body. This is also the case for those who have been pregnant before (see above). 
• Fetal position: Another factor to consider is how your baby is positioned in the uterus. For example, your baby being in a transverse position could cause your bump to be wider. 

There are many other factors that could influence the way someone’s pregnancy progresses, including age, body shape, and more. Don’t be alarmed if you think you’re showing sooner than normal or feel as though you should be showing more than you are. Be sure to speak to a healthcare provider about your concerns. Read my guide on body image during pregnancy → 

What Is Fundal Height? 

One way that your bump size will be measured during pregnancy is to calculate fundal height. Fundal height refers to the distance between the pubic bone and the top of the uterus. [2] Fundal height can help providers assess if a fetus is growing at a normal rate, what gestational age might be, and the fetus’s position. Fundal height can’t tell us much in the first few months of pregnancy, but by week 20, fundal height in centimeters should be close to the fetus’s gestational age. [2] For example, someone who is 25 weeks pregnant should have a fundal height of about 25 centimeters. 

While fundal height can be a useful measurement, it’s important to note that nothing is 100% accurate when estimating the size of a fetus in utero. If the fundal height is off by one or two centimeters, there is rarely any cause for concern. If fundal height does seem concerning, providers can follow up with additional testing or ultrasounds to get a better idea of how your pregnancy is progressing. [2] 

First Trimester (Weeks 1 to 12)

The first trimester is an exciting time full of many changes. While you’re likely experiencing many new symptoms like nausea, sore breasts, and fatigue, you may not see any hints of a bump quite yet. 

Size and Shape Progression

Even if you don’t notice much of a change in the size of your belly, your uterus has begun to expand already. In the first trimester alone, the fetus will grow from about a quarter-inch long (smaller than a grain of rice) to about the size of a plum. [3] Some people may notice a bit of bloating during the first trimester which may look or feel like the makings of a bump. It’s also possible to start showing early on, especially when taking into account some of the factors I mentioned above. 

What to Expect

As the fetus continues to grow, you are experiencing a surge of different hormones to support early pregnancy. Common symptoms include fatigue, nausea, sore boobs, mood swings, increased urination, shortness of breath, and acne or skin changes. [3] There are a lot of big developmental changes happening during the first trimester of pregnancy, which is why a nutritious diet and prenatal vitamins are so important. 

Second Trimester (Weeks 12 to 27)

Let’s move on to the second trimester, which is sometimes thought of as the sweet spot during pregnancy. The second trimester is when many people will really begin to notice a change in the size of the belly, and exciting development milestones are achieved. By the end of week 27, the baby is starting to gain fat, hair may be visible, fingerprints are forming, and the baby can respond to familiar sounds and voices. [4] 

Size and Shape Progression

The second trimester includes weeks 12 to 27 of pregnancy and is often marked by finding out the sex of the fetus, feeling the fetus move for the first time, new symptoms, and more. [4] The baby continues to grow at a fast rate during this time, and many people will start to feel and look more pregnant towards the middle or end of the second trimester. By the end of the second trimester, the fetus will be around 2 to 3 pounds and up to 16 inches long, roughly the size of a cabbage. [5] It’s common to notice more of a bump forming during this time as your baby continues to grow. Stretch marks and the linea nigra may also begin to appear depending on many factors, such as genetics, pre-pregnancy weight, etc. You may also notice that your “innie” is becoming more of an “outie”. [1] 

What to Expect

Some people find that symptoms aren’t as severe in the second trimester as they may be in the first and third. Many will find relief from morning sickness and fatigue and may enjoy feeling the baby move for the first time. Others may begin experiencing new symptoms, such as an increased appetite, food cravings, body aches, swelling, stretch marks, linea nigra, and others. 

Shop Natalist Belly Oil → 

Third Trimester (Weeks 28 to 40)

The third trimester is the last stretch of pregnancy before giving birth when the pregnant belly is at its largest. It’s common to see fluctuations in size, shape, and position of the bump. 

Size and Shape Progression

Not surprisingly, the third trimester is when the bump will be the largest. You may even feel as though your belly has to be done growing even with weeks to go. It’s likely difficult to see your legs or feet when you’re standing up, and many will report feeling a full or tight sensation in the stomach as the skin continues to stretch. [1] If you’re looking for ways to keep your belly hydrated and moisturized, try out Natalist Belly Oil! 

Around the 35-week mark, the baby is about the size and weight of a 5-pound bag of flour. [1,6] As already mentioned, there are a lot of factors that can impact whether you’re carrying high or low, when you really notice the “pop” of your bump, the shape of your belly, etc. 

What to Expect

As the due date gets closer, many pregnant people will start to feel an increase in discomfort during the final weeks of pregnancy. Many experience backaches, round ligament pain, heartburn, swelling, shortness of breath, false contractions, and more. Some may be worried about giving birth while others are thrilled that there’s an end in sight. These are the last three months that you’ll be carrying your baby inside of you, giving you a little more time to focus on newborn prep like stocking up on postnatal supplies, diapers, preparing a hospital bag, etc. 

Post-Pregnancy Belly

After you’ve given birth, it’s normal and expected that your body will feel and look a little bit different. While many providers will tell you that postpartum healing takes about six weeks, there are many other internal changes occurring for months after delivery, and in many ways, pregnancy will change your body forever. [7] Your uterus, abdominal muscles, and ligaments don’t return to their pre-pregnancy state right away, and can actually take weeks to months to restrengthen or shrink back to their normal size. [7] No one should expect their belly to look exactly the same after pregnancy, so give yourself lots of grace. Your body has done amazing things to get you where you are today! 

Natalist: Supporting You and Your Belly Every Step of the Way

At Natalist, we’ve experienced the many highs and lows that come with fertility, pregnancy, and parenting. Pregnancy causes a lot of changes that are out of our control, and everyone’s journey is different. It can be exciting to see the first hint of a baby bump during pregnancy, and it can also be frustrating if you feel as though your body doesn’t look how you thought it would. Try to avoid comparing your pregnancy to anyone else's and rely on your healthcare provider’s expertise when it comes to what’s normal vs. abnormal. Chances are you are right on track! Make it a priority to spoil yourself sometime soon, either with pregnancy-safe self-care items or preparing for the road ahead with postpartum essentials. 

We are in awe of you and your body, and you should be too! 

References:

1. Taylor, M. Wu, J. Your Pregnant Belly Size and Shape. What to Expect. June 2021. https://www.whattoexpect.com/pregnancy/ask-heidi/week-31/size-and-shape.aspx
2. Fundal Height. Cleveland Clinic. January 2022. https://my.clevelandclinic.org/health/diagnostics/22294-fundal-height
3. First Trimester. Cleveland Clinic. August 2022. https://my.clevelandclinic.org/health/articles/9699-first-trimester
4. Fetal development: The 2nd trimester. Mayo Clinic. June 2022. https://www.mayoclinic.org/healthy-lifestyle/pregnancy-week-by-week/in-depth/fetal-development/art-20046151
5. The Second Trimester. Johns Hopkins Medicine. Accessed September 2023. https://www.hopkinsmedicine.org/health/wellness-and-prevention/the-second-trimester#
6. Romano M, Cacciatore A, Giordano R, La Rosa B. Postpartum period: three distinct but continuous phases. J Prenat Med. 2010;4(2):22-25.