Pregnancy, like any other health-related experience, differs for every woman — and this includes bump size.
“Between pregnancies, (bump sizes) are going to be very different as well,” said Dr. Yolanda Kirkham, an obstetrician-gynecologist at Women’s College Hospital and St. Joseph’s Health Centre Toronto.
Kirkham points out that the first trimester differs from the third and that the further a woman is into her pregnancy, the larger a bump usually gets. But why do some women show their pregnancy earlier than others, and why are some bumps big while others look small?
Here are some factors that affect baby bump size.
Core muscles are an important muscle group and are vital to things like posture and balance. Our core also affects how far a baby bump comes out.
“If someone is very fit and does a lot of sit-ups or Pilates and has a strong core, then their rectus muscles — which are the abdominal muscles in front — are tight,” Kirkham said.
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Strong abdominal muscles mean a growing uterus is going to stay closer to the core of the body, Kirkham explained, making a bump appear smaller.
On the other hand, if core muscles have been stretched out from a previous pregnancy, a second or third pregnancy baby bump may look larger.
“Your muscles are a little bit more elastic at that point,” Kirkham said.
Weight and height
Women’s bodies are all different, and varying bump sizes reflect that.
If a woman is taller and has a longer torso, their pregnancy may not show as early as someone who is shorter, Kirkham said. Later in a pregnancy, a shorter woman’s belly may also seem wider because there is less room for the baby to move “up and down.”
A woman’s pre-pregnancy weight can also play a role in the size of their bump. While Kirkham says doctors usually encourage about 25 to 35 pounds of pregnancy weight gain, this amount varies across body sizes.
People who are underweight typically need to gain more, Kirkham says, recommending between 20 and 40 pounds.
“People who are underweight … have very little for the baby to utilize so your body actually has to make more energy stores and fat stores,” she explained. “Women that are overweight actually gain less — or sometimes even lose weight — because they have a little bit more (that) the baby can take from.”
Kirkham says a woman can determine their recommended weight on the government of Canada’s pregnancy weight gain calculator but should also talk to their doctor.
Hormones and stage of pregnancy
Typically, a bump grows as a woman’s pregnancy progresses.
“Most people don’t show before around 16 weeks or so, but everyone is going to be different,” Kirkham said.
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In the first trimester of pregnancy, a woman may experience morning sickness, which can include nausea and vomiting. If she has a hard time keeping food down, she may lose weight.
On the flip side, if someone starts gaining weight at the beginning of their pregnancy, the stomach area can look larger faster. There can also be bloating from progesterone hormones, which can cause a change in the belly’s shape as well, Kirkham said.
Visit your doctor
It’s important for pregnant women to have regular checkups with their doctor to monitor their pregnancy. A health-care provider does weight measurements as well as symphysial fundal height (SFH) measurements, which monitor fetal growth.
“That’s where we measure from the pubic bone up to the top of the uterus, and we only do that after 20 weeks,” Kirkham said. “At 20 weeks, your bump is usually up to your belly button, and then each week after that, (it grows) about a centimetre.”
Because of all the factors that can affect the size of a baby bump, Kirkham said it’s important to avoid commenting on a woman’s size. It can be upsetting and can also cause unnecessary worry or anxiety for the mom-to-be.
“Because of all the variations, it is very hard for anybody to know and compare (bump sizes) properly,” Kirkham said.
“One of the worst things you can tell a pregnant woman is that her bump is too big or too small because … somebody on the street is not going to be able to tell that.”
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