Heidi Montag looks stunning as she shows off her pregnant

Heidi Montag looks stunning as she shows off her pregnant belly in a neon green bikini

Heidi Montag-Pratt looked stunning as she showed off her pregnancy bump while on vacation in Hawaii on Sunday.

The reality TV star celebrated husband Spencer Pratt’s 39th birthday with their son Gunner Stone, four, rocking the neon green two-piece swimsuit as they explored the tropical island.

Happy, healthy, and looking pregnant, Montag redefined the term “hot mom.”

Hot Mama: Heidi Montag showed her baby bump on Sunday while on vacation in Hawaii

Hot Mama: Heidi Montag showed her baby bump on Sunday while on vacation in Hawaii

Looking relaxed and carefree, Montag rocked the neon triangle bikini set.

She wore her tie bottoms just below her baby bump, which proved flattering for the mom-to-be.

The red carpet figure looked confident in a swimsuit as she smiled for the camera

A mother's love: The beauty spent much of her time on the beach playing with son Gunner Pratt

A mother’s love: The beauty spent much of her time on the beach playing with son Gunner Pratt

Montag romped around with her firstborn in the sea and around the Hawaiian resort.

Spotted in sunglasses to match his mum’s neon swimsuit, Gunner and Montag appeared to be enjoying each other’s company while spending quality time together.

Always a doting mom, Montag, who has reached the five and a half month mark of her pregnancy, tossed her hair in a ponytail and wore a protective quartz crystal around her neck as she played with her young son in tropical paradise.

Hand in hand: A doting Montag was smiling from ear to ear as she hit the mark of five and a half months into her pregnancy while on holiday

Hand in hand: A doting Montag was smiling from ear to ear as she hit the mark of five and a half months into her pregnancy while on holiday

Montag and Pratt were spotted taking pictures for their own photo album memories.

Montag posed for the birthday girl as he snapped photos of her holding her stomach.

The couple, who met and fell in love in 2006 while filming MTV reality show The Hills, wed in 2008 and are still going strong fourteen years after their very public nuptials.

In July, the beauty admitted she was hoping for a girl, but her son is thrilled to have a baby brother.

Making memories: Montag appeared to be a pillar of strength and beauty as she awaits the arrival of her second child with crystal entrepreneur Spencer Pratt

Making memories: Montag appeared to be a pillar of strength and beauty as she awaits the arrival of her second child with crystal entrepreneur Spencer Pratt

Heidi added: “Growing up I always wanted boys and recently I’ve started to think, I don’t know, I kind of want a girl and have one of each.

“For Gunner, he really wants a brother, so ultimately I want what’s best for him and his life.”

The couple have previously struggled to conceive and will be happy as long as they have a healthy child.

Spencer said: “As long as there’s a human in her belly, that’s a win. “We’re a long way from worrying about gender in my brain. Thank God, there’s a baby here.”

The Hills star admits she started blaming herself for her fertility woes.

Heidi said: “I felt responsible.

“I felt like it was my fault… It was really hard to feel like you want something so bad and it’s just not possible… There’s nothing else I could have done.”

Beach babe with camera: Last month she shared this picture wearing a blue crop top and gray pants

Beach babe with camera: Last month she shared this picture wearing a blue crop top and gray pants

“I felt older. I felt a bit maybe broken down with that. I just felt like maybe I missed an opportunity, maybe I made a bad choice.

Heidi went to extreme lengths to try to conceive — including eating raw meat.

She previously said: “I ate bison hearts and raw meat and a lot of liver. And I’ve switched to an animal diet and I’ve had all my blood work done and I’ve donated a lot of blood. Towards the end I was really on an animal-based diet that’s mostly meat, so I really eliminated most of the veggies because they say there are oxalates and toxins that could really get in the way [pregnancy].’

The former Celebrity Big Brother star has also eliminated most fruit from her diet and found a “great lube” to increase her chances of conceiving.

Hard work: The couple have previously struggled to conceive and will be happy as long as they have a healthy child.  Spencer said:

Hard work: The couple have previously struggled to conceive and will be happy as long as they have a healthy child. Spencer said: “As long as there’s a human in her belly, that’s a win. “We’re a long way from worrying about gender in my brain. Thank you God, here’s a baby’

She said: “I had a minimum of fruit, I had basically no grains and I took a few supplements. And then I also found a lubricant that is said to be great for fertility. And it all came together in God’s timing and I got pregnant.’

Heidi went on to explain that she had actually stopped taking pregnancy tests leading up to her pregnancy and was “shocked” to find that she was expecting when her period was late.

She said: “I decided to stop pregnancy testing because every month I was so disappointed that I wasn’t pregnant. So I just thought if I’m late I’ll wait another day.

“Then the next day I waited and went downstairs like, ‘I’m just going to take the pregnancy test.’ So I took my Clear Blue pregnancy test and saw that I was pregnant. I couldn’t even believe it. I was shocked! I cried. I ran upstairs like ‘Spencer, it says pregnant!’ Gunner was like, ‘Why are you crying? What’s happening?’ ‘