A grinning young woman posted a full-length selfie to TikTok.

In the mirror pic she is wearing shorts, midriff out – nothing out of the ordinary.

…Except the text over the picture, which states: ‘Me at 8 months and had no idea’.

The video, which has almost 150,000 views in three days is just one of over 3,000 TikToks under the tag #crypticpregnancy.

Many of these videos detail women’s experiences of going to hospital thinking they have appendicitis, or feeling like they have extreme period pain – but next thing they know, they’re in labour.

So what actually is a cryptic pregnancy? And why are we seeing so many of these stories?

What is a cryptic pregnancy?

There is no official definition of cryptic pregnancy as there is debate over the timeline.

However, ‘What to Expect’ defines cryptic pregnancy, or ‘stealth pregnancy’ as when a woman is pregnant ‘but doesn’t know it, until labour begins’.

Often these types of pregnancies occur when the mum-to-be doesn’t experience any usual symptoms of pregnancy. Some have periods, no morning sickness, or no obvious bump. Others even have a negative pregnancy test.

‘My boobs got bigger and I obviously gained a little weight but it wasn’t a baby bump, just looked like I gained weight, ‘The TikToker, @alliemorgan012 explained in a comment to her video.

‘But I still had my period and everything so it was weird,’ she continued.

How common are cryptic pregnancies?

Midwife, Sarah Joy Owen explained to Netmums: ‘Cryptic pregnancies tend to be quite rare.’

This is because most women experience the telltale signs of pregnancy. She said these can include missed periods, sore breasts, nausea and sickness as well physical changes such as bigger boobs and tummy.

‘However, not all of these occur and there are genuine cases of women not realising they are having a baby until quite late into their pregnancy, or indeed until they are in labour,’ she said.

Are cryptic pregnancies becoming more common?

‘As far as I’m aware it’s not becoming more common,’ Sarah said, rather it’s a trend that more people are talking about.

‘It doesn’t happen very often but we certainly see it, and not always in first-time mums either,’ she continued.

Different research gives different stats on how common it can be – this is partly down to the lack of an official definition.

What to Expect says it’s one in every 475 pregnancies, while some research estimates it at about one in 2,500 pregnancies.

A third study put it as 325 ‘surprise births’ in the UK every year.

So why does it happen?

Cryptic pregnancy can affect anyone, however, pregnancy may be less obvious in certain people.

For example, if you have a irregular periods anyway, you may not realise you are pregnant. This may be because you have recently given birth, have PCOS, use birth control or are in perimenopause.

‘Sometimes hormone contraception can still give a breakthrough bleed,’ Sarah says, explaining that women see this to be a period.

‘But apart from that there doesn’t seem to be a reason.’

Mum guilt

Some women who experience a cryptic pregnancy can feel guilt or shame which can stop them from enjoying their first few weeks with their newborn, Sarah said.

She thinks that sharing the videos on social media is good way to help people realise ‘they are not alone and that there is nothing to feel bad about at all’.

For those who do experience cryptic pregnancy, Sarah said she would recommend counselling or a pregnancy/birth debrief to help make sense of what has happened.