The weird reason Meghan Markle's baby bump appears larger at night.

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Of the 83,496839 photos of Meghan Markle we’ve all seen over the last week, there’s one image in particular that’s started a conversation about pregnancy.

On Tuesday night, Markle attended a state dinner hosted by the President of Fiji, Jioji Konrote, wearing a Safiyaa Ginkgo cape dress in ‘Fijian blue’. But as she stood beside Prince Harry, photographers captured the clearest image so far of the 37-year-old’s growing baby bump – looking significantly more pronounced that it has in other photos.

While holding a baby bump will always accentuate it, and clothing plays a role in how large it appears, many commented that Markle may have reached that stage in pregnancy where your belly 'pops', once your uterus rises above your pubic bone.

But, interestingly, there could actually be another factor at play: baby bumps often appear larger at night.

Many women anecdotally notice this throughout their pregnancy, with some sharing before and after photos of their bumps in the morning and at night.

Speaking to Trimester Talk, doula Susannah Birch suggested the change in size throughout the day could be related to the abdominal muscles. "At night time, your abdominal muscles are tired from holding your bump [and they] loosen as they grow more tired, which allows your bump to sit out further and appear larger," she said.

In an interview with Mamamia, however, Melbourne-based obstetrician and gynaecologist Dr Joseph Sgroi said he would put a woman's evolving bump size down to a different factor.

"A lot of women will say that towards the end of the night they do feel a lot more bloated, and that bloating sensation is a combination of them obviously having eaten over the course of the day," he said.

The other component at play is progesterone.

"One of the things progesterone does, which is the primary hormone that's secreted from the placenta, is it actually slows down gut motility, so it slows down the transit time from when you eat something to when it comes out the other end," explained Dr Sgroi.

"And the reason, in part, for that is if you think of us not as women living in 2018, but rather women in 1018, where food was quite scarce, the whole idea is that if we can slow down gut motility, we can extract as much of the nutrients of the food as possible, because obviously we're needing that for a developing baby.

"Of course in 1018 that was highly important because you probably weren't getting that much food. But in 2018, where you're having three square meals a day and if not more, then that slowing down of your gut is actually, for some women, counter intuitive, because you start to get constipated and hemorrhoids and the like. So that bloating... can happen particularly in that first part of your pregnancy."

Dr Sgroi also acknowledged that given the stage of pregnancy Markle is at (it's believed she's four months pregnant), her bump will likely change noticeably over the course of the royal tour.

"For that [first trimester], the uterus is hidden within that pelvic bone, and then after about 13 weeks onwards, this uterus which is predominantly in the pelvis now starts to move to the tummy or the abdomen, and that's when you start to show more and more," he said.

"So, quite obviously, we've been taking multiple photos of an individual who's pregnant during the time where her uterus is expanding at great knots. You would think the changes would be subtle, but of course, over the course of a week, two weeks, three weeks, big changes would be normal in any woman's pregnancy."

In short: Meghan Markle's pregnancy is completely normal, as is the fact her bump might appear slightly more pronounced at night.

But that doesn't mean we'll stop noticing every little detail about it.

It's a GODDAMN ROYAL BABY BUMP for goodness sake.