The Kylie Jenner baby bump mystery: How long does it take most women to show when they're pregnant?

News broke in late September that Kylie Jenner is pregnant, but the reality star and her extended family have stayed mum about the reports. In her social media photos since then, Jenner has only shown herself in baggy clothes or in shots from the chest up.

Now, the Daily Mail has published photos it claims are the first public shots of Jenner’s bump, and the reality star is addressing them on Twitter.

In the photos, Jenner is wearing black sweatpants and a hoodie and may or may not have a hint of a belly. “First of all if you’re going to photoshop my photos blogs/paps check for the crooked lines in the background,” she captioned the photos. “2nd photo is clearly altered.” Jenner followed that up with a Snapchat photo of herself in the sweats, cozying up to her sister Khloé Kardashian, who is also reportedly pregnant. Neither one has a visible baby bump.

Kardashian also had her own “is she or isn’t she” moment on Halloween, when she posted photos on Instagram of herself in a stomach-baring costume. “She’s not pregnant,” one person wrote in the comments. “You don’t look pregnant to me,” said another.

Both sisters are reportedly around four months along — and it’s actually normal that women wouldn’t show at that point in their pregnancy. A woman’s uterus gains about a centimeter a week during her pregnancy, and at 12 weeks, the average uterus is usually at the entrance to a woman’s pelvis, so the woman wouldn’t be showing, Michael Cackovic, an ob-gyn at the Ohio State University Wexner Medical Center, tells Yahoo Lifestyle. By 20 weeks, her uterus would be up to her belly button, and she may or may not be showing, he says. “It’s not uncommon for first-time moms that are fit to not show until they’re 24, 26, or 28 weeks pregnant,” he says.

It’s different with second and subsequent pregnancies — those women typically show sooner, women’s health expert Jennifer Wider, MD, tells Yahoo Lifestyle. However, Wider points out, every woman is different.

There are a few reasons why there’s so much variation. Tall women tend to show later because they typically have more room in their torso for the baby to grow into, Christine Greves, an ob-gyn at the Winnie Palmer Hospital for Women and Babies in Orlando, tells Yahoo Lifestyle. Toned abdominal muscles can also make a woman’s bump seem smaller, as can the position of her uterus (women with a “tilted uterus” may show later than others), Greves explains.

Of course, the size of a woman’s bump doesn’t make her pregnancy any more or less viable. “There is a huge range of normal here,” Wider says. “It’s much more important to pay attention to the growth of the baby rather than what the mom looks like.”

Read more from Yahoo Lifestyle:

• The Kylie Jenner of slime reveals how she gained more than 6 million followers on YouTube

• Over-the-top baby gender reveals like Jessica Alba’s are super-trendy

• ‘I proposed to myself’: Debra Messing gave herself an engagement ring, and the internet loves it

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