A mother who is pregnant with triplets has documented her growing baby bump in extraordinary week-by-week photos.

Maria, 36, of Copenhagen, Denmark, has amassed more than 46,000 followers on Instagram with her candid posts revealing what it is really like to be expecting triplets.

The mother-of-one already shares son Mikael, two, with husband Anders, 40, and the parents are set to welcome two daughters and another son later this month, according to the Daily Mail.

On her Instagram account triplets_of_copenhagen, Maria, who is originally from Norway, shared an amazing week-to-week photo series that showed just how quickly her baby bump expanded.

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She admitted it was "strange" that her large belly could project so far outwards without support and "without falling down".

She wrote: "What a journey this has been! From the huge shock of learning there were three, to people's reactions, the numerous scannings/checks and all the preparations and planning for this life-changing event. Nothing like the ordinary.

"I'm glad we took these pictures, because this collage really shows the massive growth. It's strange to have ended up with such a big belly and it's even stranger that it can stand out like that without falling down."

Maria and Anders tied the knot earlier this year, four years after meeting on Tinder.

The couple had wanted to give Mikael a baby brother or sister but were shocked to discover they had conceived triplets without fertility treatment.

The odds of conceiving triplets without any treatment is thought to be roughly one in 4,400.

Maria revealed how they have been forced to swap their trendy hybrid SUV for a more practical minibus to fit their growing family, and have been stocking up on dozens of baby outfits in time for the new arrivals.

The parents have also had to come up with creative ways to fit the new cot, changing table and baby accessories in their 80sq m Copenhagen apartment.

Maria also shared images of her pruritic urticarial papules and plaques of pregnancy (PUPPP), a pregnancy-related rash that covered her stomach before spreading to her arms and legs.

Her honest posts about the highs and lows of pregnancy have won her hundreds of followers, many of whom respond to posts with supportive messages.

On her most recent post, which comes just days before the babies are due, one wrote: "Wishing you quiet weeks and good luck with your babies."

Another posted: "This is awesome! God bless."