1. Pregnancy
  2. Pregnancy health
  3. Staying healthy

Flo Fact-Checking Standards

Every piece of content at Flo Health adheres to the highest editorial standards for language, style, and medical accuracy. To learn what we do to deliver the best health and lifestyle insights to you, check out our content review principles.

Belly Expansion During Pregnancy: What to Expect

Belly expansion is a physical manifestation of pregnancy. While your belly usually expands because of the growing baby, a few other factors are also involved. Many pregnant people wonder when and how their belly will grow. Let’s look at these common concerns and some of the more unusual causes of belly expansion during pregnancy.

When does the belly bump start to show?

Each pregnancy is different. A few things determine when your belly bump will become noticeable and how large it will be:

  • Number of pregnancies

First-time mothers can expect a noticeable belly expansion between 12 and 16 weeks. Your pregnancy symptoms may include bloating and constipation, causing your waistband to feel tight even before 12 weeks. People who have been pregnant before tend to show earlier, as their abdominal wall has already stretched.

  • Number of fetuses

If you’re pregnant with multiples, your bump will probably be visible earlier. 

  • Body composition

In people with lower body weight, a belly bump may be noticeable earlier than in overweight people. In some cases, it may not be evident until the 20th week of pregnancy.

Take a quiz
Find out what you can do with our Health Assistant

The bump reflects the growth of the baby above the pelvic bone. In the earlier stages of pregnancy, your uterus is still under your pelvic bone, so the expansion isn’t as noticeable.

What can belly expansion involve?

People experience several signs as their belly grows during pregnancy, and most of them are completely normal. Let's discuss them in the order they may appear.

Stretch marks

Stretch marks occur as the skin on your belly expands rapidly to accommodate the growing baby. Studies say that about 43 to 88 percent of pregnant people develop stretch marks. These show up as red or pink streaks across your tummy. Your breasts and hips, which also grow during pregnancy, may develop stretch marks too.  

Some factors influence the appearance of stretch marks:

  • young age
  • family history
  • being overweight before pregnancy
  • gaining extra weight before childbirth
  • large fetal weight

Most health care providers agree that stretch marks are mostly hereditary, and topical treatment can’t stop them from occurring. However, you can try to minimize the appearance of stretch marks by maintaining a healthy diet during pregnancy. Drinking plenty of water and moisturizing regularly may also help. 

Outie belly button

Sometimes a person’s belly button may pop out as their belly expands and the umbilical tube stump pushes outward. Every pregnancy is different, so not everyone experiences these effects. Some people may even experience a certain sign with one pregnancy and not another.

Back pain

As your center of gravity shifts, your posture changes. As a result, your lower back muscles have to work harder, potentially causing chronic soreness. The abdominal muscles also influence back health by maintaining balance. During pregnancy, these muscles are stretching and cannot fully support the back. Back pain affects most people in the third trimester, when your belly is the largest. 

To minimize pain, look for comfortable shoes that support the arch of the foot, and try to avoid high heels. 

It can also be helpful to opt for clothes that support your abdomen, such as maternity pants with a wide elastic band or an abdominal binder. 

Water-based activity and swimming can help relieve symptoms of back pain.

Difficulty breathing

As the baby grows, your uterus expands into the abdominal cavity, pushing your internal organs higher underneath your rib cage. As the space in your abdomen decreases, your lungs may not be able to expand fully. The rib cage also changes its shape, making deep breaths more challenging. Studies show that around 70 percent of healthy pregnant people experience breathing difficulties. Thankfully, this resolves with the delivery of your baby. 

Rapid belly expansion: why it may occur

Other factors can influence rapid belly expansion during pregnancy.  

Date discrepancy

Your due date is measured by adding 280 days to the first day of your last period. If you’ve visited a health care provider, your due date is based on the first-trimester ultrasound. Some people who have irregular periods or did not receive an ultrasound may have additional challenges in figuring out their due date. This may make it seem like your bump is showing earlier or later than expected.

Pre-pregnancy obesity and sudden pregnancy weight gain

Health care providers generally agree that healthy people with normal body weight can expect to gain between 25 and 35 pounds during pregnancy. A lot of that weight gain will happen during the last trimester, as the baby grows more quickly.

People who gain excess weight during pregnancy may have a larger, more protruding belly. Those who were overweight or obese before conceiving may also have a larger belly bump.

Second pregnancy

Second pregnancies and beyond typically cause bumps that appear earlier. This is because the abdominal muscles have been stretched already in prior pregnancies. 

More than one baby

Mothers of multiples will often have a larger belly than women with just one fetus. After all, more babies take up more space! 

Gas and pregnancy bloating

Changes in your gastrointestinal tract are a normal part of pregnancy. Excessive gas and bloating affect lots of people, especially in the first trimester. Pregnant people may also experience constipation, especially by the second trimester. This is because of hormones that relax the intestinal muscles and the pressure of the expanding uterus on the intestines. As a result, food and waste move more slowly through your system. Increased protein intake and pregnancy vitamins with iron may also contribute to constipation.

Abnormal causes of belly expansion

In most cases, a belly bump during pregnancy is completely healthy. However, some pregnancy conditions can cause a rapidly swelling belly, requiring careful monitoring. If you experience any of these conditions, make sure to talk to a medical professional. 

1. Large fetus

A larger-than-average fetus will likely cause a larger-than-average belly bump. 

A large fetus can develop for a few reasons:

  • Male fetus: Boys are born 150 grams heavier than girls, on average.
  • Gestational diabetes: Maternal blood glucose levels can rise during pregnancy.
  • Maternal obesity: Extra weight around the abdomen can lead to a larger bump.

Folks who have a larger baby may need additional examinations and special delivery accommodations, which need to be discussed with a health care provider as early as possible.

2. Molar pregnancy

Molar pregnancies result from problems during fertilization, leading to an abnormal placenta. In a complete molar pregnancy, the sperm has fertilized a non-viable egg, and only placental tissue develops. Because the egg wasn’t viable, no fetus develops. In a partial molar pregnancy, two sperm usually fertilize one egg, and some fetal and placental tissue begins to grow. This condition is most often diagnosed in the first trimester based on symptoms like uterine enlargement and abnormal bleeding. Most molar pregnancies result in miscarriage. 

3. Polyhydramnios

This term refers to excess amniotic fluid in the uterus. This can lead to preterm labor and contractions. Although 20 percent of cases of polyhydramnios are associated with congenital fetal abnormalities, in almost 70 percent of these pregnancies, the cause remains unknown. This condition should be closely monitored by a health care provider.

4. Large ovarian tumor

Large ovarian tumors can be spotted during routine ultrasounds during pregnancy. If you’re certain you’re not pregnant but have a fast-growing belly, your health care provider may order an ultrasound to check for large ovarian tumors. People with these tumors can develop other symptoms such as bloating, dull pain, and heaviness in the lower abdomen. Specific treatments will be determined by what the health care provider finds.

5. Fast-growing benign fibroid tumors

These occur when muscle cell fibers quickly come together into masses within the uterine wall. Despite their name, these growths are harmless and often observed on ultrasounds conducted during pregnancy.

Fibroid tumors cause abdominal swelling, pain, and difficulty urinating, all of which are similar to pregnancy symptoms. Sometimes the size of the tumor does not affect symptoms. If you’re not sure what’s causing your symptoms, contact a health care provider.

When will a belly bump disappear after delivery?

The uterus takes time to return to its pre-pregnancy size. After two weeks, it is no longer visible or felt through the abdomen, and by six weeks, its size will be roughly back to normal. As your belly shrinks, you may feel cramping and soreness. Breastfeeding your baby can help release hormones that naturally shrink your uterus.

Generally, your weight gain in pregnancy, level of activity, diet, and genetics all affect how quickly your belly returns to its pre-pregnancy size.

People who have had a C-section may experience swelling around the incision site. Scar tissue can also cause additional swelling. Individuals who gained excess weight during pregnancy, had a large fetus, or carried multiples may notice prolonged belly swelling. Generally, your weight gain in pregnancy, level of activity, diet, and genetics all affect how quickly your belly returns to its pre-pregnancy size. 

“1st trimester pregnancy: What to expect” Mayo Clinic, MFMER, Accessed Feb. 26, 2020, https://www.mayoclinic.org/healthy-lifestyle/pregnancy-week-by-week/in-depth/pregnancy/art-20047208

Uwe Wollina, Alberto Goldman “Management of stretch marks (with a focus on striae rubrae).” National Center for Biotechnology Information, U.S. National Library of Medicine, Accessed Jul 2017, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5782435/

Amanda M. Oakley, Bhupendra C. Patel.” Stretch Marks” NCBI, Bookshelf, August 10, 2020, https://www.ncbi.nlm.nih.gov/books/NBK436005/

Rita V. Vora, Rajat Gupta, Malay J. Mehta, Arvind H. Chaudhari, Abhishek P. Pilani, Nidhi Patel “Pregnancy and Skin.” National Center for Biotechnology Information, U.S. National Library of Medicine, Accessed Oct 2014, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4311336/

“Back Pain During Pregnancy.” The American College of Obstetricians and Gynecologists, FAQ115, May 2020, https://www.acog.org/womens-health/faqs/back-pain-during-pregnancy

Antonella LoMauro, Andrea Aliverti “Respiratory physiology of pregnancy” National Center for Biotechnology Information, U.S. National Library of Medicine, Accessed Dec 2015, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4818213/

Merit Kullinger, Michaela Granfors, Helle Kieler, Alkistis Skalkidou “Discrepancy between pregnancy dating methods affects obstetric and neonatal outcomes: a population-based register cohort study” National Center for Biotechnology Information, U.S. National Library of Medicine, Accessed May 2018, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5932022/

Yvonne Butler Tobah “Why do abdominal muscles sometimes separate during pregnancy?” Mayo Clinic, MFMER, Accessed Aug. 18, 2020, https://www.mayoclinic.org/healthy-lifestyle/pregnancy-week-by-week/expert-answers/diastasis-recti/faq-20057825

Catarina Frias Gomes, Mónica Sousa, Inês Lourenço, Diana Martins, Joana Torresa “ Gastrointestinal diseases during pregnancy: what does the gastroenterologist need to know?” National Center for Biotechnology Information, U.S. National Library of Medicine, Accessed Apr 27,2018, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6033757/

Abiodun M. Akanmode, Heba Mahdy “Macrosomia” NCBI, Bookshelf, Accessed August 23, 2020, https://www.ncbi.nlm.nih.gov/books/NBK557577/

Shaina Bruce, Joel Sorosky. “ Gestational Trophoblastic Disease”,NCBI, Bookshelf, Accessed August 26, 2020, https://www.ncbi.nlm.nih.gov/books/NBK470267/

Jemma Johns "The postpartum ultrasound scan" Ultrasound, The British Medical Ultrasound Society, Accessed Jun 2016, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5105363/#:~:text=The%20uterine%20mass%20decreases%20by,with%20a%20non-pregnant%20state.

Read this next