In which month of pregnancy tummy comes out

• If it's your first pregnancy, you'll probably start to show at 12 to 16 weeks. 
• You'll likely show early if you're short, carrying multiple babies, or you've been pregnant before.
• By week 20, your doctor will start measuring your baby bump to track fetal growth.

Pregnancy bumps are as diverse as the babies they produce. 

You start to show in pregnancy at 12 to 16 weeks 

If it's your first pregnancy, you'll probably start to show between 12 to 16 weeks, around the start of your second trimester. But this initial bump is not from the baby. In fact, at 15 weeks, the average fetus is 4 inches long, or about as large as an orange. 

So that "baby bump" isn't from the baby's size, but rather the expansion of your uterus.

"As the uterus gets bigger with a developing pregnancy, the loops of bowel which fill the abdomen are pushed upwards and out to the sides," says Meg Wilson, MBBS, an OB-GYN at London Gynaecology.

What causes some to show early in pregnancy?

There are a few factors that might affect when you start showing: 

• Height: If you have a short abdomen, your bump will likely pop out sooner than for taller women with a longer abdomen. "Women who have a long abdomen may have more space for their uterus to develop upwards rather than outwards, which can give the appearance of a smaller bump," Wilson says.  
• Weight: If you're smaller with less body fat, you'll probably show much earlier than someone with more body fat. 
• Multiple buns in the oven: If you're carrying twins or multiples, you're more likely to show earlier — as early as 6 weeks. That's because your uterus will expand more to create space for the additional fetuses. 
• Not your first rodeo: You're more likely to show early if this isn't your first pregnancy.  "The uterus is held in position at the front by the abdominal walls: skin and muscle strength," says Wilson. "For women who have had several pregnancies, the skin and muscle become weaker and the pregnant uterus can fall forward more."

How doctors track baby bump progression

By week 20, your doctor will start measuring your fundal length — that's the distance between the pubic bone and the top of the uterus. Typically, this number should correlate with your week of pregnancy.

So, for example, if your fundal length is 25 centimeters, you should be in or near your 25th week of pregnancy. 

If, however, your fundal length is too high, it could indicate growth problems with the baby, like fetal macrosomia, which is when a baby is significantly too large. 

On the flip side, if your fundal length is too low it could mean restricted growth, which is when the baby isn't large enough. While not all small babies suffer from restricted growth, it's worth checking in with your maternal health practitioner if you are concerned. 

Insider's takeaway

There are several factors that affect when your baby bump will start to show during pregnancy. 

When it's your first pregnancy, it's common for your bump to start showing between 12 and 16 weeks. The initial baby bump is caused by the expansion of the uterus, rather than the size of the fetus.

If you have a short abdomen, less body fat, are carrying multiple fetuses, or it's not your first pregnancy, then you are more likely to show early. 

Your doctor will begin measuring your fundal length by week 20. This measurement helps doctors track fetal growth.

Rebecca Cairns is a freelance writer for Insider. 

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If it's your first pregnancy, or even if it isn't, you may be wondering when your bloated belly will turn into a baby bump, and your pregnancy will start to show. The short answer: It can be different for everyone, for a number of reasons.

When do you start showing in pregnancy?

First-time moms usually start showing sometime between 12 and 18 weeks. In a BabyCenter poll, most women expecting their first child said they started to show between 12 and 18 weeks, very closely followed by those who said that their bump emerged between 18 and 24 weeks.

Every woman and every baby bump is different, and there isn't an exact time when you'll start "showing," which is what happens when your growing uterus begins to expand above the pubic bone. This usually starts when you're around 12 weeks pregnant; before then, the uterus remains within the pelvis and isn't usually visible.

Even at 12 weeks of pregnancy, any “bump” you start to see in your abdomen is really just your bowels that used to be in your pelvis, now being pushed up higher in your belly. "Showing" starts as your abdomen looks fuller and you find yourself needing to unbutton your pants by the end of the day. From there, a distinctly uterus-shaped bump will appear in another few weeks or so.

Several factors play a part in how and when you start showing:

• Your body shape and size. Shorter women may start showing earlier than tall women, and thinner women may see a distinct baby bump before plus-size women do.
• Your core muscles. Women with weak core muscles may start showing earlier than those with a stronger core.
• The position of your uterus.
• Whether not this is your first pregnancy. Moms who've already been pregnant often start showing with their second pregnancy sooner, since their uterine and abdominal muscles have been stretched from an earlier pregnancy.

Sometimes, you might think you're already showing early on in the first trimester, but it's more than likely just pregnancy bloating, a swelling that can make your pants fit tighter. Bloating is one of the early signs of pregnancy, along with gas and constipation.

Should I be worried if I haven't started showing yet?

If you haven't started showing and feel like you don't look pregnant yet, don't fret. There are a number of completely normal factors that may be contributing to how pregnant you look. Showing late doesn't automatically mean that your baby is too small. In the second trimester, your ob-gyn or midwife will start monitoring your fundal height to track your baby's growth, and if there's any reason for concern, they'll do an ultrasound to check on the progress. Babies who are smaller than expected for their gestational age will get frequent monitoring to make sure they're doing well.

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